shmem.c 105 KB
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/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *		 2000 Transmeta Corp.
 *		 2000-2001 Christoph Rohland
 *		 2000-2001 SAP AG
 *		 2002 Red Hat Inc.
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 * Copyright (C) 2002-2011 Hugh Dickins.
 * Copyright (C) 2011 Google Inc.
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 * Copyright (C) 2002-2005 VERITAS Software Corporation.
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 * Copyright (C) 2004 Andi Kleen, SuSE Labs
 *
 * Extended attribute support for tmpfs:
 * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
 * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
 *
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 * tiny-shmem:
 * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
 *
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 * This file is released under the GPL.
 */

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#include <linux/fs.h>
#include <linux/init.h>
#include <linux/vfs.h>
#include <linux/mount.h>
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#include <linux/ramfs.h>
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#include <linux/pagemap.h>
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#include <linux/file.h>
#include <linux/mm.h>
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#include <linux/sched/signal.h>
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#include <linux/export.h>
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#include <linux/swap.h>
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#include <linux/uio.h>
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#include <linux/khugepaged.h>
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#include <linux/hugetlb.h>
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#include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */

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static struct vfsmount *shm_mnt;

#ifdef CONFIG_SHMEM
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/*
 * This virtual memory filesystem is heavily based on the ramfs. It
 * extends ramfs by the ability to use swap and honor resource limits
 * which makes it a completely usable filesystem.
 */

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#include <linux/xattr.h>
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#include <linux/exportfs.h>
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#include <linux/posix_acl.h>
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#include <linux/posix_acl_xattr.h>
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#include <linux/mman.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
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#include <linux/pagevec.h>
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#include <linux/percpu_counter.h>
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#include <linux/falloc.h>
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#include <linux/splice.h>
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#include <linux/security.h>
#include <linux/swapops.h>
#include <linux/mempolicy.h>
#include <linux/namei.h>
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#include <linux/ctype.h>
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#include <linux/migrate.h>
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#include <linux/highmem.h>
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#include <linux/seq_file.h>
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#include <linux/magic.h>
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#include <linux/syscalls.h>
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#include <linux/fcntl.h>
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#include <uapi/linux/memfd.h>
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#include <linux/userfaultfd_k.h>
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#include <linux/rmap.h>
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#include <linux/uuid.h>
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#include <linux/uaccess.h>
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#include <asm/pgtable.h>

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#include "internal.h"

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#define BLOCKS_PER_PAGE  (PAGE_SIZE/512)
#define VM_ACCT(size)    (PAGE_ALIGN(size) >> PAGE_SHIFT)
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/* Pretend that each entry is of this size in directory's i_size */
#define BOGO_DIRENT_SIZE 20

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/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128

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/*
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 * shmem_fallocate communicates with shmem_fault or shmem_writepage via
 * inode->i_private (with i_mutex making sure that it has only one user at
 * a time): we would prefer not to enlarge the shmem inode just for that.
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 */
struct shmem_falloc {
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	wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
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	pgoff_t start;		/* start of range currently being fallocated */
	pgoff_t next;		/* the next page offset to be fallocated */
	pgoff_t nr_falloced;	/* how many new pages have been fallocated */
	pgoff_t nr_unswapped;	/* how often writepage refused to swap out */
};

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#ifdef CONFIG_TMPFS
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static unsigned long shmem_default_max_blocks(void)
{
	return totalram_pages / 2;
}

static unsigned long shmem_default_max_inodes(void)
{
	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
}
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#endif
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static bool shmem_should_replace_page(struct page *page, gfp_t gfp);
static int shmem_replace_page(struct page **pagep, gfp_t gfp,
				struct shmem_inode_info *info, pgoff_t index);
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static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
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		struct page **pagep, enum sgp_type sgp,
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		gfp_t gfp, struct vm_area_struct *vma,
		struct vm_fault *vmf, int *fault_type);
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int shmem_getpage(struct inode *inode, pgoff_t index,
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		struct page **pagep, enum sgp_type sgp)
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{
	return shmem_getpage_gfp(inode, index, pagep, sgp,
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		mapping_gfp_mask(inode->i_mapping), NULL, NULL, NULL);
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}
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static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
{
	return sb->s_fs_info;
}

/*
 * shmem_file_setup pre-accounts the whole fixed size of a VM object,
 * for shared memory and for shared anonymous (/dev/zero) mappings
 * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
 * consistent with the pre-accounting of private mappings ...
 */
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
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	return (flags & VM_NORESERVE) ?
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		0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
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}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
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	if (!(flags & VM_NORESERVE))
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		vm_unacct_memory(VM_ACCT(size));
}

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static inline int shmem_reacct_size(unsigned long flags,
		loff_t oldsize, loff_t newsize)
{
	if (!(flags & VM_NORESERVE)) {
		if (VM_ACCT(newsize) > VM_ACCT(oldsize))
			return security_vm_enough_memory_mm(current->mm,
					VM_ACCT(newsize) - VM_ACCT(oldsize));
		else if (VM_ACCT(newsize) < VM_ACCT(oldsize))
			vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize));
	}
	return 0;
}

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/*
 * ... whereas tmpfs objects are accounted incrementally as
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 * pages are allocated, in order to allow large sparse files.
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 * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
 * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
 */
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static inline int shmem_acct_block(unsigned long flags, long pages)
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{
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	if (!(flags & VM_NORESERVE))
		return 0;

	return security_vm_enough_memory_mm(current->mm,
			pages * VM_ACCT(PAGE_SIZE));
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}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
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	if (flags & VM_NORESERVE)
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		vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
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}

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static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

	if (shmem_acct_block(info->flags, pages))
		return false;

	if (sbinfo->max_blocks) {
		if (percpu_counter_compare(&sbinfo->used_blocks,
					   sbinfo->max_blocks - pages) > 0)
			goto unacct;
		percpu_counter_add(&sbinfo->used_blocks, pages);
	}

	return true;

unacct:
	shmem_unacct_blocks(info->flags, pages);
	return false;
}

static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

	if (sbinfo->max_blocks)
		percpu_counter_sub(&sbinfo->used_blocks, pages);
	shmem_unacct_blocks(info->flags, pages);
}

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static const struct super_operations shmem_ops;
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static const struct address_space_operations shmem_aops;
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static const struct file_operations shmem_file_operations;
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static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
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static const struct vm_operations_struct shmem_vm_ops;
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static struct file_system_type shmem_fs_type;
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bool vma_is_shmem(struct vm_area_struct *vma)
{
	return vma->vm_ops == &shmem_vm_ops;
}

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static LIST_HEAD(shmem_swaplist);
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static DEFINE_MUTEX(shmem_swaplist_mutex);
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static int shmem_reserve_inode(struct super_block *sb)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
	if (sbinfo->max_inodes) {
		spin_lock(&sbinfo->stat_lock);
		if (!sbinfo->free_inodes) {
			spin_unlock(&sbinfo->stat_lock);
			return -ENOSPC;
		}
		sbinfo->free_inodes--;
		spin_unlock(&sbinfo->stat_lock);
	}
	return 0;
}

static void shmem_free_inode(struct super_block *sb)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
	if (sbinfo->max_inodes) {
		spin_lock(&sbinfo->stat_lock);
		sbinfo->free_inodes++;
		spin_unlock(&sbinfo->stat_lock);
	}
}

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/**
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 * shmem_recalc_inode - recalculate the block usage of an inode
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 * @inode: inode to recalc
 *
 * We have to calculate the free blocks since the mm can drop
 * undirtied hole pages behind our back.
 *
 * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
 * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
 *
 * It has to be called with the spinlock held.
 */
static void shmem_recalc_inode(struct inode *inode)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
	long freed;

	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
	if (freed > 0) {
		info->alloced -= freed;
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		inode->i_blocks -= freed * BLOCKS_PER_PAGE;
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		shmem_inode_unacct_blocks(inode, freed);
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	}
}

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bool shmem_charge(struct inode *inode, long pages)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
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	unsigned long flags;
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	if (!shmem_inode_acct_block(inode, pages))
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		return false;
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	spin_lock_irqsave(&info->lock, flags);
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	info->alloced += pages;
	inode->i_blocks += pages * BLOCKS_PER_PAGE;
	shmem_recalc_inode(inode);
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	spin_unlock_irqrestore(&info->lock, flags);
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	inode->i_mapping->nrpages += pages;

	return true;
}

void shmem_uncharge(struct inode *inode, long pages)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
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	unsigned long flags;
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	spin_lock_irqsave(&info->lock, flags);
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	info->alloced -= pages;
	inode->i_blocks -= pages * BLOCKS_PER_PAGE;
	shmem_recalc_inode(inode);
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	spin_unlock_irqrestore(&info->lock, flags);
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	shmem_inode_unacct_blocks(inode, pages);
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}

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/*
 * Replace item expected in radix tree by a new item, while holding tree lock.
 */
static int shmem_radix_tree_replace(struct address_space *mapping,
			pgoff_t index, void *expected, void *replacement)
{
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	struct radix_tree_node *node;
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	void __rcu **pslot;
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	void *item;
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	VM_BUG_ON(!expected);
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	VM_BUG_ON(!replacement);
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	item = __radix_tree_lookup(&mapping->i_pages, index, &node, &pslot);
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	if (!item)
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		return -ENOENT;
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	if (item != expected)
		return -ENOENT;
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	__radix_tree_replace(&mapping->i_pages, node, pslot,
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			     replacement, NULL);
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	return 0;
}

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/*
 * Sometimes, before we decide whether to proceed or to fail, we must check
 * that an entry was not already brought back from swap by a racing thread.
 *
 * Checking page is not enough: by the time a SwapCache page is locked, it
 * might be reused, and again be SwapCache, using the same swap as before.
 */
static bool shmem_confirm_swap(struct address_space *mapping,
			       pgoff_t index, swp_entry_t swap)
{
	void *item;

	rcu_read_lock();
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	item = radix_tree_lookup(&mapping->i_pages, index);
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	rcu_read_unlock();
	return item == swp_to_radix_entry(swap);
}

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/*
 * Definitions for "huge tmpfs": tmpfs mounted with the huge= option
 *
 * SHMEM_HUGE_NEVER:
 *	disables huge pages for the mount;
 * SHMEM_HUGE_ALWAYS:
 *	enables huge pages for the mount;
 * SHMEM_HUGE_WITHIN_SIZE:
 *	only allocate huge pages if the page will be fully within i_size,
 *	also respect fadvise()/madvise() hints;
 * SHMEM_HUGE_ADVISE:
 *	only allocate huge pages if requested with fadvise()/madvise();
 */

#define SHMEM_HUGE_NEVER	0
#define SHMEM_HUGE_ALWAYS	1
#define SHMEM_HUGE_WITHIN_SIZE	2
#define SHMEM_HUGE_ADVISE	3

/*
 * Special values.
 * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled:
 *
 * SHMEM_HUGE_DENY:
 *	disables huge on shm_mnt and all mounts, for emergency use;
 * SHMEM_HUGE_FORCE:
 *	enables huge on shm_mnt and all mounts, w/o needing option, for testing;
 *
 */
#define SHMEM_HUGE_DENY		(-1)
#define SHMEM_HUGE_FORCE	(-2)

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#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
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/* ifdef here to avoid bloating shmem.o when not necessary */

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static int shmem_huge __read_mostly;
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#if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
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static int shmem_parse_huge(const char *str)
{
	if (!strcmp(str, "never"))
		return SHMEM_HUGE_NEVER;
	if (!strcmp(str, "always"))
		return SHMEM_HUGE_ALWAYS;
	if (!strcmp(str, "within_size"))
		return SHMEM_HUGE_WITHIN_SIZE;
	if (!strcmp(str, "advise"))
		return SHMEM_HUGE_ADVISE;
	if (!strcmp(str, "deny"))
		return SHMEM_HUGE_DENY;
	if (!strcmp(str, "force"))
		return SHMEM_HUGE_FORCE;
	return -EINVAL;
}

static const char *shmem_format_huge(int huge)
{
	switch (huge) {
	case SHMEM_HUGE_NEVER:
		return "never";
	case SHMEM_HUGE_ALWAYS:
		return "always";
	case SHMEM_HUGE_WITHIN_SIZE:
		return "within_size";
	case SHMEM_HUGE_ADVISE:
		return "advise";
	case SHMEM_HUGE_DENY:
		return "deny";
	case SHMEM_HUGE_FORCE:
		return "force";
	default:
		VM_BUG_ON(1);
		return "bad_val";
	}
}
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#endif
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static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
		struct shrink_control *sc, unsigned long nr_to_split)
{
	LIST_HEAD(list), *pos, *next;
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	LIST_HEAD(to_remove);
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	struct inode *inode;
	struct shmem_inode_info *info;
	struct page *page;
	unsigned long batch = sc ? sc->nr_to_scan : 128;
	int removed = 0, split = 0;

	if (list_empty(&sbinfo->shrinklist))
		return SHRINK_STOP;

	spin_lock(&sbinfo->shrinklist_lock);
	list_for_each_safe(pos, next, &sbinfo->shrinklist) {
		info = list_entry(pos, struct shmem_inode_info, shrinklist);

		/* pin the inode */
		inode = igrab(&info->vfs_inode);

		/* inode is about to be evicted */
		if (!inode) {
			list_del_init(&info->shrinklist);
			removed++;
			goto next;
		}

		/* Check if there's anything to gain */
		if (round_up(inode->i_size, PAGE_SIZE) ==
				round_up(inode->i_size, HPAGE_PMD_SIZE)) {
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			list_move(&info->shrinklist, &to_remove);
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			removed++;
			goto next;
		}

		list_move(&info->shrinklist, &list);
next:
		if (!--batch)
			break;
	}
	spin_unlock(&sbinfo->shrinklist_lock);

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	list_for_each_safe(pos, next, &to_remove) {
		info = list_entry(pos, struct shmem_inode_info, shrinklist);
		inode = &info->vfs_inode;
		list_del_init(&info->shrinklist);
		iput(inode);
	}

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	list_for_each_safe(pos, next, &list) {
		int ret;

		info = list_entry(pos, struct shmem_inode_info, shrinklist);
		inode = &info->vfs_inode;

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		if (nr_to_split && split >= nr_to_split)
			goto leave;
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		page = find_get_page(inode->i_mapping,
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				(inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
		if (!page)
			goto drop;

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		/* No huge page at the end of the file: nothing to split */
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		if (!PageTransHuge(page)) {
			put_page(page);
			goto drop;
		}

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		/*
		 * Leave the inode on the list if we failed to lock
		 * the page at this time.
		 *
		 * Waiting for the lock may lead to deadlock in the
		 * reclaim path.
		 */
		if (!trylock_page(page)) {
			put_page(page);
			goto leave;
		}

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		ret = split_huge_page(page);
		unlock_page(page);
		put_page(page);

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		/* If split failed leave the inode on the list */
		if (ret)
			goto leave;
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		split++;
drop:
		list_del_init(&info->shrinklist);
		removed++;
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leave:
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		iput(inode);
	}

	spin_lock(&sbinfo->shrinklist_lock);
	list_splice_tail(&list, &sbinfo->shrinklist);
	sbinfo->shrinklist_len -= removed;
	spin_unlock(&sbinfo->shrinklist_lock);

	return split;
}

static long shmem_unused_huge_scan(struct super_block *sb,
		struct shrink_control *sc)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

	if (!READ_ONCE(sbinfo->shrinklist_len))
		return SHRINK_STOP;

	return shmem_unused_huge_shrink(sbinfo, sc, 0);
}

static long shmem_unused_huge_count(struct super_block *sb,
		struct shrink_control *sc)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
	return READ_ONCE(sbinfo->shrinklist_len);
}
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#else /* !CONFIG_TRANSPARENT_HUGE_PAGECACHE */
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#define shmem_huge SHMEM_HUGE_DENY

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static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
		struct shrink_control *sc, unsigned long nr_to_split)
{
	return 0;
}
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#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */
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static inline bool is_huge_enabled(struct shmem_sb_info *sbinfo)
{
	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
	    (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge) &&
	    shmem_huge != SHMEM_HUGE_DENY)
		return true;
	return false;
}

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/*
 * Like add_to_page_cache_locked, but error if expected item has gone.
 */
static int shmem_add_to_page_cache(struct page *page,
				   struct address_space *mapping,
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				   pgoff_t index, void *expected)
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{
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	int error, nr = hpage_nr_pages(page);
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	VM_BUG_ON_PAGE(PageTail(page), page);
	VM_BUG_ON_PAGE(index != round_down(index, nr), page);
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	VM_BUG_ON_PAGE(!PageLocked(page), page);
	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
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	VM_BUG_ON(expected && PageTransHuge(page));
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	page_ref_add(page, nr);
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	page->mapping = mapping;
	page->index = index;

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	xa_lock_irq(&mapping->i_pages);
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	if (PageTransHuge(page)) {
		void __rcu **results;
		pgoff_t idx;
		int i;

		error = 0;
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		if (radix_tree_gang_lookup_slot(&mapping->i_pages,
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					&results, &idx, index, 1) &&
				idx < index + HPAGE_PMD_NR) {
			error = -EEXIST;
		}

		if (!error) {
			for (i = 0; i < HPAGE_PMD_NR; i++) {
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				error = radix_tree_insert(&mapping->i_pages,
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						index + i, page + i);
				VM_BUG_ON(error);
			}
			count_vm_event(THP_FILE_ALLOC);
		}
	} else if (!expected) {
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		error = radix_tree_insert(&mapping->i_pages, index, page);
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	} else {
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		error = shmem_radix_tree_replace(mapping, index, expected,
								 page);
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	}

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	if (!error) {
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		mapping->nrpages += nr;
		if (PageTransHuge(page))
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			__inc_node_page_state(page, NR_SHMEM_THPS);
		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
		__mod_node_page_state(page_pgdat(page), NR_SHMEM, nr);
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		xa_unlock_irq(&mapping->i_pages);
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	} else {
		page->mapping = NULL;
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		xa_unlock_irq(&mapping->i_pages);
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		page_ref_sub(page, nr);
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	}
	return error;
}

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/*
 * Like delete_from_page_cache, but substitutes swap for page.
 */
static void shmem_delete_from_page_cache(struct page *page, void *radswap)
{
	struct address_space *mapping = page->mapping;
	int error;

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	VM_BUG_ON_PAGE(PageCompound(page), page);

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	xa_lock_irq(&mapping->i_pages);
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	error = shmem_radix_tree_replace(mapping, page->index, page, radswap);
	page->mapping = NULL;
	mapping->nrpages--;
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	__dec_node_page_state(page, NR_FILE_PAGES);
	__dec_node_page_state(page, NR_SHMEM);
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	xa_unlock_irq(&mapping->i_pages);
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	put_page(page);
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	BUG_ON(error);
}

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/*
 * Remove swap entry from radix tree, free the swap and its page cache.
 */
static int shmem_free_swap(struct address_space *mapping,
			   pgoff_t index, void *radswap)
{
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	void *old;
673

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	xa_lock_irq(&mapping->i_pages);
	old = radix_tree_delete_item(&mapping->i_pages, index, radswap);
	xa_unlock_irq(&mapping->i_pages);
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	if (old != radswap)
		return -ENOENT;
	free_swap_and_cache(radix_to_swp_entry(radswap));
	return 0;
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}

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/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
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 * given offsets are swapped out.
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 *
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 * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
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 * as long as the inode doesn't go away and racy results are not a problem.
 */
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unsigned long shmem_partial_swap_usage(struct address_space *mapping,
						pgoff_t start, pgoff_t end)
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{
	struct radix_tree_iter iter;
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	void __rcu **slot;
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	struct page *page;
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	unsigned long swapped = 0;
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	rcu_read_lock();

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	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
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		if (iter.index >= end)
			break;

		page = radix_tree_deref_slot(slot);

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		if (radix_tree_deref_retry(page)) {
			slot = radix_tree_iter_retry(&iter);
			continue;
		}
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		if (radix_tree_exceptional_entry(page))
			swapped++;

		if (need_resched()) {
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			slot = radix_tree_iter_resume(slot, &iter);
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			cond_resched_rcu();
		}
	}

	rcu_read_unlock();

	return swapped << PAGE_SHIFT;
}

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/*
 * Determine (in bytes) how many of the shmem object's pages mapped by the
 * given vma is swapped out.
 *
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 * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
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 * as long as the inode doesn't go away and racy results are not a problem.
 */
unsigned long shmem_swap_usage(struct vm_area_struct *vma)
{
	struct inode *inode = file_inode(vma->vm_file);
	struct shmem_inode_info *info = SHMEM_I(inode);
	struct address_space *mapping = inode->i_mapping;
	unsigned long swapped;

	/* Be careful as we don't hold info->lock */
	swapped = READ_ONCE(info->swapped);

	/*
	 * The easier cases are when the shmem object has nothing in swap, or
	 * the vma maps it whole. Then we can simply use the stats that we
	 * already track.
	 */
	if (!swapped)
		return 0;

	if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size)
		return swapped << PAGE_SHIFT;

	/* Here comes the more involved part */
	return shmem_partial_swap_usage(mapping,
			linear_page_index(vma, vma->vm_start),
			linear_page_index(vma, vma->vm_end));
}

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/*
 * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
 */
void shmem_unlock_mapping(struct address_space *mapping)
{
	struct pagevec pvec;
	pgoff_t indices[PAGEVEC_SIZE];
	pgoff_t index = 0;

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	pagevec_init(&pvec);
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	/*
	 * Minor point, but we might as well stop if someone else SHM_LOCKs it.
	 */
	while (!mapping_unevictable(mapping)) {
		/*
		 * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
		 * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
		 */
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		pvec.nr = find_get_entries(mapping, index,
					   PAGEVEC_SIZE, pvec.pages, indices);
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		if (!pvec.nr)
			break;
		index = indices[pvec.nr - 1] + 1;
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		pagevec_remove_exceptionals(&pvec);
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		check_move_unevictable_pages(pvec.pages, pvec.nr);
		pagevec_release(&pvec);
		cond_resched();
	}
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}

/*
 * Remove range of pages and swap entries from radix tree, and free them.
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 * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
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 */
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static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
								 bool unfalloc)
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{
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	struct address_space *mapping = inode->i_mapping;
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	struct shmem_inode_info *info = SHMEM_I(inode);
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	pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT;
	pgoff_t end = (lend + 1) >> PAGE_SHIFT;
	unsigned int partial_start = lstart & (PAGE_SIZE - 1);
	unsigned int partial_end = (lend + 1) & (PAGE_SIZE - 1);
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	struct pagevec pvec;
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	pgoff_t indices[PAGEVEC_SIZE];
	long nr_swaps_freed = 0;
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	pgoff_t index;
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	int i;

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	if (lend == -1)
		end = -1;	/* unsigned, so actually very big */
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	pagevec_init(&pvec);
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	index = start;
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	while (index < end) {
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		pvec.nr = find_get_entries(mapping, index,
			min(end - index, (pgoff_t)PAGEVEC_SIZE),
			pvec.pages, indices);
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		if (!pvec.nr)
			break;
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		for (i = 0; i < pagevec_count(&pvec); i++) {
			struct page *page = pvec.pages[i];

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			index = indices[i];
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			if (index >= end)
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				break;

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			if (radix_tree_exceptional_entry(page)) {
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				if (unfalloc)
					continue;
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				nr_swaps_freed += !shmem_free_swap(mapping,
								index, page);
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				continue;
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			}

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			VM_BUG_ON_PAGE(page_to_pgoff(page) != index, page);

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			if (!trylock_page(page))
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				continue;
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			if (PageTransTail(page)) {
				/* Middle of THP: zero out the page */
				clear_highpage(page);
				unlock_page(page);
				continue;
			} else if (PageTransHuge(page)) {
				if (index == round_down(end, HPAGE_PMD_NR)) {
					/*
					 * Range ends in the middle of THP:
					 * zero out the page
					 */
					clear_highpage(page);
					unlock_page(page);
					continue;
				}
				index += HPAGE_PMD_NR - 1;
				i += HPAGE_PMD_NR - 1;
			}

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			if (!unfalloc || !PageUptodate(page)) {
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				VM_BUG_ON_PAGE(PageTail(page), page);
				if (page_mapping(page) == mapping) {
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					VM_BUG_ON_PAGE(PageWriteback(page), page);
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					truncate_inode_page(mapping, page);
				}
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			}
			unlock_page(page);
		}
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		pagevec_remove_exceptionals(&pvec);
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		pagevec_release(&pvec);
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		cond_resched();
		index++;
	}
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	if (partial_start) {
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		struct page *page = NULL;
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		shmem_getpage(inode, start - 1, &page, SGP_READ);
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		if (page) {
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			unsigned int top = PAGE_SIZE;
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			if (start > end) {
				top = partial_end;
				partial_end = 0;
			}
			zero_user_segment(page, partial_start, top);
			set_page_dirty(page);
			unlock_page(page);
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			put_page(page);
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		}
	}
	if (partial_end) {
		struct page *page = NULL;
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		shmem_getpage(inode, end, &page, SGP_READ);
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		if (page) {
			zero_user_segment(page, 0, partial_end);
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			set_page_dirty(page);
			unlock_page(page);
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			put_page(page);
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		}
	}
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	if (start >= end)
		return;
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	index = start;
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	while (index < end) {
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		cond_resched();
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		pvec.nr = find_get_entries(mapping, index,
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				min(end - index, (pgoff_t)PAGEVEC_SIZE),
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				pvec.pages, indices);
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		if (!pvec.nr) {
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			/* If all gone or hole-punch or unfalloc, we're done */
			if (index == start || end != -1)
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				break;
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			/* But if truncating, restart to make sure all gone */
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			index = start;
			continue;
		}
		for (i = 0; i < pagevec_count(&pvec); i++) {
			struct page *page = pvec.pages[i];

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			index = indices[i];
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			if (index >= end)
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				break;

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			if (radix_tree_exceptional_entry(page)) {
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				if (unfalloc)
					continue;
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				if (shmem_free_swap(mapping, index, page)) {
					/* Swap was replaced by page: retry */
					index--;
					break;
				}
				nr_swaps_freed++;
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				continue;
			}

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			lock_page(page);
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			if (PageTransTail(page)) {
				/* Middle of THP: zero out the page */
				clear_highpage(page);
				unlock_page(page);
				/*
				 * Partial thp truncate due 'start' in middle
				 * of THP: don't need to look on these pages
				 * again on !pvec.nr restart.
				 */
				if (index != round_down(end, HPAGE_PMD_NR))
					start++;
				continue;
			} else if (PageTransHuge(page)) {
				if (index == round_down(end, HPAGE_PMD_NR)) {
					/*
					 * Range ends in the middle of THP:
					 * zero out the page
					 */
					clear_highpage(page);
					unlock_page(page);
					continue;
				}
				index += HPAGE_PMD_NR - 1;
				i += HPAGE_PMD_NR - 1;
			}

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			if (!unfalloc || !PageUptodate(page)) {
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				VM_BUG_ON_PAGE(PageTail(page), page);
				if (page_mapping(page) == mapping) {
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					VM_BUG_ON_PAGE(PageWriteback(page), page);
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					truncate_inode_page(mapping, page);
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				} else {
					/* Page was replaced by swap: retry */
					unlock_page(page);
					index--;
					break;
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				}
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			}
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			unlock_page(page);
		}
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		pagevec_remove_exceptionals(&pvec);
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		pagevec_release(&pvec);
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		index++;
	}
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	spin_lock_irq(&info->lock);
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	info->swapped -= nr_swaps_freed;
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	shmem_recalc_inode(inode);
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	spin_unlock_irq(&info->lock);
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}
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void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
	shmem_undo_range(inode, lstart, lend, false);
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	inode->i_ctime = inode->i_mtime = current_time(inode);
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}
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EXPORT_SYMBOL_GPL(shmem_truncate_range);
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static int shmem_getattr(const struct path *path, struct kstat *stat,
			 u32 request_mask, unsigned int query_flags)
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{
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	struct inode *inode = path->dentry->d_inode;
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	struct shmem_inode_info *info = SHMEM_I(inode);
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	struct shmem_sb_info *sb_info = SHMEM_SB(inode->i_sb);
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1002
	if (info->alloced - info->swapped != inode->i_mapping->nrpages) {
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		spin_lock_irq(&info->lock);
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		shmem_recalc_inode(inode);
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		spin_unlock_irq(&info->lock);
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	}
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	generic_fillattr(inode, stat);
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	if (is_huge_enabled(sb_info))
		stat->blksize = HPAGE_PMD_SIZE;

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	return 0;
}

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static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
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{
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	struct inode *inode = d_inode(dentry);
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	struct shmem_inode_info *info = SHMEM_I(inode);
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	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
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	int error;

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	error = setattr_prepare(dentry, attr);
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	if (error)
		return error;

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	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
		loff_t oldsize = inode->i_size;
		loff_t newsize = attr->ia_size;
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		/* protected by i_mutex */
		if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
		    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
			return -EPERM;

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		if (newsize != oldsize) {
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			error = shmem_reacct_size(SHMEM_I(inode)->flags,
					oldsize, newsize);
			if (error)
				return error;
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			i_size_write(inode, newsize);
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			inode->i_ctime = inode->i_mtime = current_time(inode);
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		}
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		if (newsize <= oldsize) {
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			loff_t holebegin = round_up(newsize, PAGE_SIZE);
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			if (oldsize > holebegin)
				unmap_mapping_range(inode->i_mapping,
							holebegin, 0, 1);
			if (info->alloced)
				shmem_truncate_range(inode,
							newsize, (loff_t)-1);
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			/* unmap again to remove racily COWed private pages */
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			if (oldsize > holebegin)
				unmap_mapping_range(inode->i_mapping,
							holebegin, 0, 1);
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			/*
			 * Part of the huge page can be beyond i_size: subject
			 * to shrink under memory pressure.
			 */
			if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
				spin_lock(&sbinfo->shrinklist_lock);
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				/*
				 * _careful to defend against unlocked access to
				 * ->shrink_list in shmem_unused_huge_shrink()
				 */
				if (list_empty_careful(&info->shrinklist)) {
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					list_add_tail(&info->shrinklist,
							&sbinfo->shrinklist);
					sbinfo->shrinklist_len++;
				}
				spin_unlock(&sbinfo->shrinklist_lock);
			}
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		}
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	}

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	setattr_copy(inode, attr);
	if (attr->ia_valid & ATTR_MODE)
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		error = posix_acl_chmod(inode, inode->i_mode);
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	return error;
}

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static void shmem_evict_inode(struct inode *inode)
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{
	struct shmem_inode_info *info = SHMEM_I(inode);
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	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
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	if (inode->i_mapping->a_ops == &shmem_aops) {
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		shmem_unacct_size(info->flags, inode->i_size);
		inode->i_size = 0;
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		shmem_truncate_range(inode, 0, (loff_t)-1);
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		if (!list_empty(&info->shrinklist)) {
			spin_lock(&sbinfo->shrinklist_lock);
			if (!list_empty(&info->shrinklist)) {
				list_del_init(&info->shrinklist);
				sbinfo->shrinklist_len--;
			}
			spin_unlock(&sbinfo->shrinklist_lock);
		}
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		if (!list_empty(&info->swaplist)) {
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			mutex_lock(&shmem_swaplist_mutex);
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			list_del_init(&info->swaplist);
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			mutex_unlock(&shmem_swaplist_mutex);
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		}
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	}
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	simple_xattrs_free(&info->xattrs);
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	WARN_ON(inode->i_blocks);
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	shmem_free_inode(inode->i_sb);
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	clear_inode(inode);
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}

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static unsigned long find_swap_entry(struct radix_tree_root *root, void *item)
{
	struct radix_tree_iter iter;
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	void __rcu **slot;
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	unsigned long found = -1;
	unsigned int checked = 0;

	rcu_read_lock();
	radix_tree_for_each_slot(slot, root, &iter, 0) {
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		void *entry = radix_tree_deref_slot(slot);

		if (radix_tree_deref_retry(entry)) {
			slot = radix_tree_iter_retry(&iter);
			continue;
		}
		if (entry == item) {
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			found = iter.index;
			break;
		}
		checked++;
		if ((checked % 4096) != 0)
			continue;
		slot = radix_tree_iter_resume(slot, &iter);
		cond_resched_rcu();
	}

	rcu_read_unlock();
	return found;
}

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/*
 * If swap found in inode, free it and move page from swapcache to filecache.
 */
1145
static int shmem_unuse_inode(struct shmem_inode_info *info,
1146
			     swp_entry_t swap, struct page **pagep)
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{
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	struct address_space *mapping = info->vfs_inode.i_mapping;
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	void *radswap;
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	pgoff_t index;
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	gfp_t gfp;
	int error = 0;
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	radswap = swp_to_radix_entry(swap);
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	index = find_swap_entry(&mapping->i_pages, radswap);
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	if (index == -1)
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		return -EAGAIN;	/* tell shmem_unuse we found nothing */
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	/*
	 * Move _head_ to start search for next from here.
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	 * But be careful: shmem_evict_inode checks list_empty without taking
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	 * mutex, and there's an instant in list_move_tail when info->swaplist
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	 * would appear empty, if it were the only one on shmem_swaplist.
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	 */
	if (shmem_swaplist.next != &info->swaplist)
		list_move_tail(&shmem_swaplist, &info->swaplist);
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	gfp = mapping_gfp_mask(mapping);
	if (shmem_should_replace_page(*pagep, gfp)) {
		mutex_unlock(&shmem_swaplist_mutex);
		error = shmem_replace_page(pagep, gfp, info, index);
		mutex_lock(&shmem_swaplist_mutex);
		/*
		 * We needed to drop mutex to make that restrictive page
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		 * allocation, but the inode might have been freed while we
		 * dropped it: although a racing shmem_evict_inode() cannot
		 * complete without emptying the radix_tree, our page lock
		 * on this swapcache page is not enough to prevent that -
		 * free_swap_and_cache() of our swap entry will only
		 * trylock_page(), removing swap from radix_tree whatever.
		 *
		 * We must not proceed to shmem_add_to_page_cache() if the
		 * inode has been freed, but of course we cannot rely on
		 * inode or mapping or info to check that.  However, we can
		 * safely check if our swap entry is still in use (and here
		 * it can't have got reused for another page): if it's still
		 * in use, then the inode cannot have been freed yet, and we
		 * can safely proceed (if it's no longer in use, that tells
		 * nothing about the inode, but we don't need to unuse swap).
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		 */
		if (!page_swapcount(*pagep))
			error = -ENOENT;
	}

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	/*
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	 * We rely on shmem_swaplist_mutex, not only to protect the swaplist,
	 * but also to hold up shmem_evict_inode(): so inode cannot be freed
	 * beneath us (pagelock doesn't help until the page is in pagecache).
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	 */
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	if (!error)
		error = shmem_add_to_page_cache(*pagep, mapping, index,
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						radswap);
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	if (error != -ENOMEM) {
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		/*
		 * Truncation and eviction use free_swap_and_cache(), which
		 * only does trylock page: if we raced, best clean up here.
		 */
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		delete_from_swap_cache(*pagep);
		set_page_dirty(*pagep);
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		if (!error) {
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			spin_lock_irq(&info->lock);
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			info->swapped--;
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			spin_unlock_irq(&info->lock);
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			swap_free(swap);
		}
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	}
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	return error;
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}

/*
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 * Search through swapped inodes to find and replace swap by page.
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 */
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int shmem_unuse(swp_entry_t swap, struct page *page)
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{
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	struct list_head *this, *next;
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	struct shmem_inode_info *info;
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	struct mem_cgroup *memcg;
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	int error = 0;

	/*
	 * There's a faint possibility that swap page was replaced before
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	 * caller locked it: caller will come back later with the right page.
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	 */
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	if (unlikely(!PageSwapCache(page) || page_private(page) != swap.val))
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		goto out;
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	/*
	 * Charge page using GFP_KERNEL while we can wait, before taking
	 * the shmem_swaplist_mutex which might hold up shmem_writepage().
	 * Charged back to the user (not to caller) when swap account is used.
	 */
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	error = mem_cgroup_try_charge(page, current->mm, GFP_KERNEL, &memcg,
			false);
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	if (error)
		goto out;
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	/* No radix_tree_preload: swap entry keeps a place for page in tree */
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	error = -EAGAIN;
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	mutex_lock(&shmem_swaplist_mutex);
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	list_for_each_safe(this, next, &shmem_swaplist) {
		info = list_entry(this, struct shmem_inode_info, swaplist);
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		if (info->swapped)
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			error = shmem_unuse_inode(info, swap, &page);
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		else
			list_del_init(&info->swaplist);
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		cond_resched();
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		if (error != -EAGAIN)
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			break;
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		/* found nothing in this: move on to search the next */
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	}
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	mutex_unlock(&shmem_swaplist_mutex);
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	if (error) {
		if (error != -ENOMEM)
			error = 0;
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		mem_cgroup_cancel_charge(page, memcg, false);
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	} else
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		mem_cgroup_commit_charge(page, memcg, true, false);
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out:
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	unlock_page(page);
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	put_page(page);
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	return error;
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}

/*
 * Move the page from the page cache to the swap cache.
 */
static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
	struct shmem_inode_info *info;
	struct address_space *mapping;
	struct inode *inode;
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	swp_entry_t swap;
	pgoff_t index;
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	VM_BUG_ON_PAGE(PageCompound(page), page);
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	BUG_ON(!PageLocked(page));
	mapping = page->mapping;
	index = page->index;
	inode = mapping->host;
	info = SHMEM_I(inode);
	if (info->flags & VM_LOCKED)
		goto redirty;
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	if (!total_swap_pages)
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		goto redirty;

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	/*
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	 * Our capabilities prevent regular writeback or sync from ever calling
	 * shmem_writepage; but a stacking filesystem might use ->writepage of
	 * its underlying filesystem, in which case tmpfs should write out to
	 * swap only in response to memory pressure, and not for the writeback
	 * threads or sync.
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	 */
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	if (!wbc->for_reclaim) {
		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
		goto redirty;
	}
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	/*
	 * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
	 * value into swapfile.c, the only way we can correctly account for a
	 * fallocated page arriving here is now to initialize it and write it.
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	 *
	 * That's okay for a page already fallocated earlier, but if we have
	 * not yet completed the fallocation, then (a) we want to keep track
	 * of this page in case we have to undo it, and (b) it may not be a
	 * good idea to continue anyway, once we're pushing into swap.  So
	 * reactivate the page, and let shmem_fallocate() quit when too many.
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	 */
	if (!PageUptodate(page)) {
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		if (inode->i_private) {
			struct shmem_falloc *shmem_falloc;
			spin_lock(&inode->i_lock);
			shmem_falloc = inode->i_private;
			if (shmem_falloc &&
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			    !shmem_falloc->waitq &&
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			    index >= shmem_falloc->start &&
			    index < shmem_falloc->next)
				shmem_falloc->nr_unswapped++;
			else
				shmem_falloc = NULL;
			spin_unlock(&inode->i_lock);
			if (shmem_falloc)
				goto redirty;
		}
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		clear_highpage(page);
		flush_dcache_page(page);
		SetPageUptodate(page);
	}

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	swap = get_swap_page(page);
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	if (!swap.val)
		goto redirty;
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	/*
	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
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	 * if it's not already there.  Do it now before the page is
	 * moved to swap cache, when its pagelock no longer protects
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	 * the inode from eviction.  But don't unlock the mutex until
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	 * we've incremented swapped, because shmem_unuse_inode() will
	 * prune a !swapped inode from the swaplist under this mutex.
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	 */
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	mutex_lock(&shmem_swaplist_mutex);
	if (list_empty(&info->swaplist))
		list_add_tail(&info->swaplist, &shmem_swaplist);
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	if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
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		spin_lock_irq(&info->lock);
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