Commit 2c136579 authored by Fengguang Wu's avatar Fengguang Wu Committed by Linus Torvalds

writeback: fix time ordering of the per superblock inode lists 8

Streamline the management of dirty inode lists and fix time ordering bugs.

The writeback logic used to move not-yet-expired dirty inodes from s_dirty to
s_io, *only to* move them back.  The move-inodes-back-and-forth thing is a
mess, which is eliminated by this patch.

The new scheme is:
- s_dirty acts as a time ordered io delaying queue;
- s_io/s_more_io together acts as an io dispatching queue.

On kupdate writeback, we pull some inodes from s_dirty to s_io at the start of
every full scan of s_io.  Otherwise  (i.e. for sync/throttle/background
writeback), we always pull from s_dirty on each run (a partial scan).

Note that the line
	list_splice_init(&sb->s_more_io, &sb->s_io);
is moved to queue_io() to leave s_io empty. Otherwise a big dirtied file will
sit in s_io for a long time, preventing new expired inodes to get in.

Cc: Ken Chen <kenchen@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarFengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0e0f4fc2
......@@ -119,7 +119,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
goto out;
/*
* If the inode was already on s_dirty or s_io, don't
* If the inode was already on s_dirty/s_io/s_more_io, don't
* reposition it (that would break s_dirty time-ordering).
*/
if (!was_dirty) {
......@@ -172,6 +172,33 @@ static void requeue_io(struct inode *inode)
list_move(&inode->i_list, &inode->i_sb->s_more_io);
}
/*
* Move expired dirty inodes from @delaying_queue to @dispatch_queue.
*/
static void move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
unsigned long *older_than_this)
{
while (!list_empty(delaying_queue)) {
struct inode *inode = list_entry(delaying_queue->prev,
struct inode, i_list);
if (older_than_this &&
time_after(inode->dirtied_when, *older_than_this))
break;
list_move(&inode->i_list, dispatch_queue);
}
}
/*
* Queue all expired dirty inodes for io, eldest first.
*/
static void queue_io(struct super_block *sb,
unsigned long *older_than_this)
{
list_splice_init(&sb->s_more_io, sb->s_io.prev);
move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
}
/*
* Write a single inode's dirty pages and inode data out to disk.
* If `wait' is set, wait on the writeout.
......@@ -222,7 +249,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
/*
* We didn't write back all the pages. nfs_writepages()
* sometimes bales out without doing anything. Redirty
* the inode. It is moved from s_io onto s_dirty.
* the inode; Move it from s_io onto s_more_io/s_dirty.
*/
/*
* akpm: if the caller was the kupdate function we put
......@@ -235,10 +262,9 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
*/
if (wbc->for_kupdate) {
/*
* For the kupdate function we leave the inode
* at the head of sb_dirty so it will get more
* writeout as soon as the queue becomes
* uncongested.
* For the kupdate function we move the inode
* to s_more_io so it will get more writeout as
* soon as the queue becomes uncongested.
*/
inode->i_state |= I_DIRTY_PAGES;
requeue_io(inode);
......@@ -296,10 +322,10 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
/*
* We're skipping this inode because it's locked, and we're not
* doing writeback-for-data-integrity. Move it to the head of
* s_dirty so that writeback can proceed with the other inodes
* on s_io. We'll have another go at writing back this inode
* when the s_dirty iodes get moved back onto s_io.
* doing writeback-for-data-integrity. Move it to s_more_io so
* that writeback can proceed with the other inodes on s_io.
* We'll have another go at writing back this inode when we
* completed a full scan of s_io.
*/
requeue_io(inode);
......@@ -366,7 +392,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
const unsigned long start = jiffies; /* livelock avoidance */
if (!wbc->for_kupdate || list_empty(&sb->s_io))
list_splice_init(&sb->s_dirty, &sb->s_io);
queue_io(sb, wbc->older_than_this);
while (!list_empty(&sb->s_io)) {
struct inode *inode = list_entry(sb->s_io.prev,
......@@ -411,13 +437,6 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
if (time_after(inode->dirtied_when, start))
break;
/* Was this inode dirtied too recently? */
if (wbc->older_than_this && time_after(inode->dirtied_when,
*wbc->older_than_this)) {
list_splice_init(&sb->s_io, sb->s_dirty.prev);
break;
}
/* Is another pdflush already flushing this queue? */
if (current_is_pdflush() && !writeback_acquire(bdi))
break;
......@@ -446,10 +465,6 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
if (wbc->nr_to_write <= 0)
break;
}
if (list_empty(&sb->s_io))
list_splice_init(&sb->s_more_io, &sb->s_io);
return; /* Leave any unwritten inodes on s_io */
}
......@@ -459,7 +474,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
* Note:
* We don't need to grab a reference to superblock here. If it has non-empty
* ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
* past sync_inodes_sb() until both the ->s_dirty and ->s_io lists are
* past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
* empty. Since __sync_single_inode() regains inode_lock before it finally moves
* inode from superblock lists we are OK.
*
......
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