The patch titled
readahead: split ondemand readahead interface into two functions
has been added to the -mm tree. Its filename is
readahead-split-ondemand-readahead-interface-into-two-functions.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: readahead: split ondemand readahead interface into two functions
From: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
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: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ext3/dir.c | 4 -
fs/ext4/dir.c | 4 -
fs/splice.c | 6 +-
include/linux/mm.h | 20 ++++++---
mm/filemap.c | 10 ++--
mm/readahead.c | 95 ++++++++++++++++++++++++++-----------------
6 files changed, 84 insertions(+), 55 deletions(-)
diff -puN fs/ext3/dir.c~readahead-split-ondemand-readahead-interface-into-two-functions fs/ext3/dir.c
--- a/fs/ext3/dir.c~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/fs/ext3/dir.c
@@ -139,10 +139,10 @@ static int ext3_readdir(struct file * fi
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);
}
diff -puN fs/ext4/dir.c~readahead-split-ondemand-readahead-interface-into-two-functions fs/ext4/dir.c
--- a/fs/ext4/dir.c~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/fs/ext4/dir.c
@@ -138,10 +138,10 @@ static int ext4_readdir(struct file * fi
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);
}
diff -puN fs/splice.c~readahead-split-ondemand-readahead-interface-into-two-functions fs/splice.c
--- a/fs/splice.c~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/fs/splice.c
@@ -304,8 +304,8 @@ __generic_file_splice_read(struct file *
* readahead/allocate the rest.
*/
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);
while (spd.nr_pages < nr_pages) {
/*
@@ -360,7 +360,7 @@ __generic_file_splice_read(struct file *
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);
/*
diff -puN include/linux/mm.h~readahead-split-ondemand-readahead-interface-into-two-functions include/linux/mm.h
--- a/include/linux/mm.h~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/include/linux/mm.h
@@ -1150,12 +1150,20 @@ int do_page_cache_readahead(struct addre
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 */
diff -puN mm/filemap.c~readahead-split-ondemand-readahead-interface-into-two-functions mm/filemap.c
--- a/mm/filemap.c~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/mm/filemap.c
@@ -887,15 +887,15 @@ void do_generic_mapping_read(struct addr
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);
}
@@ -1359,14 +1359,14 @@ retry_find:
*/
if (VM_SequentialReadHint(vma)) {
if (!page) {
- page_cache_readahead_ondemand(mapping, ra, file, page,
+ page_cache_sync_readahead(mapping, ra, file,
fdata->pgoff, 1);
page = find_lock_page(mapping, fdata->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,
fdata->pgoff, 1);
}
}
diff -puN mm/readahead.c~readahead-split-ondemand-readahead-interface-into-two-functions mm/readahead.c
--- a/mm/readahead.c~readahead-split-ondemand-readahead-interface-into-two-functions
+++ a/mm/readahead.c
@@ -351,7 +351,7 @@ static unsigned long get_next_ra_size(st
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 */
@@ -379,7 +379,7 @@ ondemand_readahead(struct address_space
* 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);
}
@@ -400,7 +400,7 @@ ondemand_readahead(struct address_space
* 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);
}
@@ -413,50 +413,71 @@ fill_ra:
}
/**
- * 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;
+ return;
- 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;
- }
+ /* 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);
_
Patches currently in -mm which might be from wfg@xxxxxxxxxxxxxxxx are
readahead-introduce-pg_readahead.patch
readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch
readahead-min_ra_pages-max_ra_pages-macros.patch
readahead-data-structure-and-routines.patch
readahead-on-demand-readahead-logic.patch
readahead-convert-filemap-invocations.patch
readahead-convert-splice-invocations.patch
readahead-convert-ext3-ext4-invocations.patch
readahead-remove-the-old-algorithm.patch
readahead-move-synchronous-readahead-call-out-of-splice-loop.patch
readahead-pass-real-splice-size.patch
mm-share-pg_readahead-and-pg_reclaim.patch
readahead-split-ondemand-readahead-interface-into-two-functions.patch
readahead-sanify-file_ra_state-names.patch
-
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