Commit cf914a7d authored by Rusty Russell's avatar Rusty Russell Committed by Linus Torvalds
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readahead: split ondemand readahead interface into two functions



Split ondemand readahead interface into two functions.  I think this makes it
a little clearer for non-readahead experts (like Rusty).

Internally they both call ondemand_readahead(), but the page argument is
changed to an obvious boolean flag.
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
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 fe3cba17
......@@ -139,10 +139,10 @@ static int ext3_readdir(struct file * filp,
pgoff_t index = map_bh.b_blocknr >>
(PAGE_CACHE_SHIFT - inode->i_blkbits);
if (!ra_has_index(&filp->f_ra, index))
page_cache_readahead_ondemand(
page_cache_sync_readahead(
sb->s_bdev->bd_inode->i_mapping,
&filp->f_ra, filp,
NULL, index, 1);
index, 1);
filp->f_ra.prev_index = index;
bh = ext3_bread(NULL, inode, blk, 0, &err);
}
......
......@@ -138,10 +138,10 @@ static int ext4_readdir(struct file * filp,
pgoff_t index = map_bh.b_blocknr >>
(PAGE_CACHE_SHIFT - inode->i_blkbits);
if (!ra_has_index(&filp->f_ra, index))
page_cache_readahead_ondemand(
page_cache_sync_readahead(
sb->s_bdev->bd_inode->i_mapping,
&filp->f_ra, filp,
NULL, index, 1);
index, 1);
filp->f_ra.prev_index = index;
bh = ext4_bread(NULL, inode, blk, 0, &err);
}
......
......@@ -295,8 +295,8 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
* readahead/allocate the rest and fill in the holes.
*/
if (spd.nr_pages < nr_pages)
page_cache_readahead_ondemand(mapping, &in->f_ra, in,
NULL, index, req_pages - spd.nr_pages);
page_cache_sync_readahead(mapping, &in->f_ra, in,
index, req_pages - spd.nr_pages);
error = 0;
while (spd.nr_pages < nr_pages) {
......@@ -352,7 +352,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
page = pages[page_nr];
if (PageReadahead(page))
page_cache_readahead_ondemand(mapping, &in->f_ra, in,
page_cache_async_readahead(mapping, &in->f_ra, in,
page, index, req_pages - page_nr);
/*
......
......@@ -1138,12 +1138,20 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
pgoff_t offset, unsigned long nr_to_read);
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
pgoff_t offset, unsigned long nr_to_read);
unsigned long page_cache_readahead_ondemand(struct address_space *mapping,
struct file_ra_state *ra,
struct file *filp,
struct page *page,
pgoff_t offset,
unsigned long size);
void page_cache_sync_readahead(struct address_space *mapping,
struct file_ra_state *ra,
struct file *filp,
pgoff_t offset,
unsigned long size);
void page_cache_async_readahead(struct address_space *mapping,
struct file_ra_state *ra,
struct file *filp,
struct page *pg,
pgoff_t offset,
unsigned long size);
unsigned long max_sane_readahead(unsigned long nr);
/* Do stack extension */
......
......@@ -894,15 +894,15 @@ void do_generic_mapping_read(struct address_space *mapping,
find_page:
page = find_get_page(mapping, index);
if (!page) {
page_cache_readahead_ondemand(mapping,
&ra, filp, page,
page_cache_sync_readahead(mapping,
&ra, filp,
index, last_index - index);
page = find_get_page(mapping, index);
if (unlikely(page == NULL))
goto no_cached_page;
}
if (PageReadahead(page)) {
page_cache_readahead_ondemand(mapping,
page_cache_async_readahead(mapping,
&ra, filp, page,
index, last_index - index);
}
......@@ -1348,14 +1348,14 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
*/
if (VM_SequentialReadHint(vma)) {
if (!page) {
page_cache_readahead_ondemand(mapping, ra, file, page,
page_cache_sync_readahead(mapping, ra, file,
vmf->pgoff, 1);
page = find_lock_page(mapping, vmf->pgoff);
if (!page)
goto no_cached_page;
}
if (PageReadahead(page)) {
page_cache_readahead_ondemand(mapping, ra, file, page,
page_cache_async_readahead(mapping, ra, file, page,
vmf->pgoff, 1);
}
}
......
......@@ -359,7 +359,7 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
static unsigned long
ondemand_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
struct page *page, pgoff_t offset,
bool hit_readahead_marker, pgoff_t offset,
unsigned long req_size)
{
unsigned long max; /* max readahead pages */
......@@ -387,7 +387,7 @@ ondemand_readahead(struct address_space *mapping,
* Standalone, small read.
* Read as is, and do not pollute the readahead state.
*/
if (!page && !sequential) {
if (!hit_readahead_marker && !sequential) {
return __do_page_cache_readahead(mapping, filp,
offset, req_size, 0);
}
......@@ -408,7 +408,7 @@ ondemand_readahead(struct address_space *mapping,
* E.g. interleaved reads.
* Not knowing its readahead pos/size, bet on the minimal possible one.
*/
if (page) {
if (hit_readahead_marker) {
ra_index++;
ra_size = min(4 * ra_size, max);
}
......@@ -421,50 +421,71 @@ ondemand_readahead(struct address_space *mapping,
}
/**
* page_cache_readahead_ondemand - generic file readahead
* page_cache_sync_readahead - generic file readahead
* @mapping: address_space which holds the pagecache and I/O vectors
* @ra: file_ra_state which holds the readahead state
* @filp: passed on to ->readpage() and ->readpages()
* @page: the page at @offset, or NULL if non-present
* @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
* @offset: start offset into @mapping, in pagecache page-sized units
* @req_size: hint: total size of the read which the caller is performing in
* PAGE_CACHE_SIZE units
* pagecache pages
*
* page_cache_readahead_ondemand() is the entry point of readahead logic.
* This function should be called when it is time to perform readahead:
* 1) @page == NULL
* A cache miss happened, time for synchronous readahead.
* 2) @page != NULL && PageReadahead(@page)
* A look-ahead hit occured, time for asynchronous readahead.
* page_cache_sync_readahead() should be called when a cache miss happened:
* it will submit the read. The readahead logic may decide to piggyback more
* pages onto the read request if access patterns suggest it will improve
* performance.
*/
unsigned long
page_cache_readahead_ondemand(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
struct page *page, pgoff_t offset,
unsigned long req_size)
void page_cache_sync_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
pgoff_t offset, unsigned long req_size)
{
/* no read-ahead */
if (!ra->ra_pages)
return 0;
if (page) {
/*
* It can be PG_reclaim.
*/
if (PageWriteback(page))
return 0;
ClearPageReadahead(page);
/*
* Defer asynchronous read-ahead on IO congestion.
*/
if (bdi_read_congested(mapping->backing_dev_info))
return 0;
}
return;
/* do read-ahead */
ondemand_readahead(mapping, ra, filp, false, offset, req_size);
}
EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
/**
* page_cache_async_readahead - file readahead for marked pages
* @mapping: address_space which holds the pagecache and I/O vectors
* @ra: file_ra_state which holds the readahead state
* @filp: passed on to ->readpage() and ->readpages()
* @page: the page at @offset which has the PG_readahead flag set
* @offset: start offset into @mapping, in pagecache page-sized units
* @req_size: hint: total size of the read which the caller is performing in
* pagecache pages
*
* page_cache_async_ondemand() should be called when a page is used which
* has the PG_readahead flag: this is a marker to suggest that the application
* has used up enough of the readahead window that we should start pulling in
* more pages. */
void
page_cache_async_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
struct page *page, pgoff_t offset,
unsigned long req_size)
{
/* no read-ahead */
if (!ra->ra_pages)
return;
/*
* Same bit is used for PG_readahead and PG_reclaim.
*/
if (PageWriteback(page))
return;
ClearPageReadahead(page);
/*
* Defer asynchronous read-ahead on IO congestion.
*/
if (bdi_read_congested(mapping->backing_dev_info))
return;
/* do read-ahead */
return ondemand_readahead(mapping, ra, filp, page,
offset, req_size);
ondemand_readahead(mapping, ra, filp, true, offset, req_size);
}
EXPORT_SYMBOL_GPL(page_cache_readahead_ondemand);
EXPORT_SYMBOL_GPL(page_cache_async_readahead);
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