[PATCH 0/9] mmap read-around and readahead take 2

[PATCH 0/9] mmap read-around and readahead take 2

[Fengguang Wu]

Andrew,

Here are the mmap read-around related patches initiated by Linus.
They are for linux-2.6.24-rc5-mm1. They're mainly about code cleanups.
The only major new feature - auto detection and early readahead for mmap
sequential reads - shows about 2% speedup on single stream case, and should
perform much better in multiple streams case.

This take: simplified patch 2, from
         mm/filemap.c |  192 +++++++++++++++++++++++++++++++++++++++-------------------
         1 files changed, 130 insertions(+), 62 deletions(-)
to
	 mm/filemap.c |  156 +++++++++++++++++++++++++++----------------------
	 1 file changed, 89 insertions(+), 67 deletions(-)


[PATCH 1/9] readahead: simplify readahead call scheme
[PATCH 2/9] readahead: clean up and simplify the code for filemap page fault readahead
[PATCH 3/9] readahead: auto detection of sequential mmap reads
[PATCH 4/9] readahead: quick startup on sequential mmap readahead
[PATCH 5/9] readahead: make ra_submit() non-static
[PATCH 6/9] readahead: save mmap read-around states in file_ra_state
[PATCH 7/9] readahead: remove unused do_page_cache_readahead()
[PATCH 8/9] readahead: move max_sane_readahead() calls into force_page_cache_readahead()
[PATCH 9/9] readahead: call max_sane_readahead() in ondemand_readahead()

Thank you,
Fengguang
-- 

[PATCH 1/9] readahead: simplify readahead call scheme

[Fengguang Wu]

[-- Attachment #1: readahead-merge-sync-async.patch --]
[-- Type: text/plain, Size: 1668 bytes --]

It is insane and error-prone to insist on the call sites to check for async
readahead after doing any sync one. I.e. whenever someone do a sync readahead:

				if (!page)
					page_cache_sync_readahead(...);

He must try async readahead, too:

				page = find_get_page(...);
				if (PageReadahead(page))
					page_cache_async_readahead(...);

The tricky point is that PG_readahead could be set by a sync readahead for the
_current_ newly faulted in page, and the readahead code simply expects one more
callback to handle it. If the caller fails to do so, it will miss the
PG_readahead bits and never able to start an async readahead.

Avoid it by piggy-backing the async part _inside_ the readahead code.

Now if an async readahead should be started immediately after a sync one,
the readahead logic itself will do it. So the following code becomes valid:

				if (!page)
					page_cache_sync_readahead(...);
				else if (PageReadahead(page))
					page_cache_async_readahead(...);

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/readahead.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc5-mm1/mm/readahead.c
@@ -402,6 +402,14 @@ ondemand_readahead(struct address_space 
 	ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
 
 readit:
+	/*
+	 * An async readahead should be triggered immediately.
+	 * Instead of demanding all call sites to check for async readahead
+	 * immediate after a sync one, start the async part now and here.
+	 */
+	if (!hit_readahead_marker && ra->size == ra->async_size)
+		ra->size *= 2;
+
 	return ra_submit(ra, mapping, filp);
 }
 

-- 

[PATCH 2/9] readahead: clean up and simplify the code for filemap page fault readahead

[Fengguang Wu]

[-- Attachment #1: readahead-standalone-mmap-readaround.patch --]
[-- Type: text/plain, Size: 8677 bytes --]

From: Linus Torvalds <torvalds@linux-foundation.org>

This shouldn't really change behavior all that much, but the single
rather complex function with read-ahead inside a loop etc is broken up
into more manageable pieces.

The behaviour is also less subtle, with the read-ahead being done up-front 
rather than inside some subtle loop and thus avoiding the now unnecessary 
extra state variables (ie "did_readaround" is gone).

Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

Ok, so this is something I did in Mexico when I wasn't scuba-diving, and 
was "watching" the kids at the pool. It was brought on by looking at git 
mmap file behaviour under cold-cache behaviour: git does ok, but my laptop 
disk is really slow, and I tried to verify that the kernel did a 
reasonable job of read-ahead when taking page faults.

I think it did, but quite frankly, the filemap_fault() code was totally 
unreadable. So this separates out the read-ahead cases, and adds more 
comments, and also changes it so that we do asynchronous read-ahead 
*before* we actually wait for the page we are waiting for to become 
unlocked.

Not that it seems to make any real difference on my laptop, but I really 
hated how it was doing a

	page = get_lock_page(..)

and then doing read-ahead after that: which just guarantees that we have 
to wait for any out-standing IO on "page" to complete before we can even 
submit any new read-ahead! That just seems totally broken!

So it replaces the "get_lock_page()" at the top with a broken-out page 
cache lookup, which allows us to look at the page state flags and make 
appropriate decisions on what we should do without waiting for the locked 
bit to clear.

It does add many more lines than it removes:

	 mm/filemap.c |  192 +++++++++++++++++++++++++++++++++++++++-------------------
	 1 files changed, 130 insertions(+), 62 deletions(-)

but that's largely due to (a) the new function headers etc due to the 
split-up and (b) new or extended comments especially about the helper 
functions. The code, in many ways, is actually simpler, apart from the 
fairly trivial expansion of the equivalent of "get_lock_page()" into the 
function.

Comments? I tried to avoid changing the read-ahead logic itself, although 
the old code did some strange things like doing *both* async readahead and 
then looking up the page and doing sync readahead (which I think was just 
due to the code being so damn messily organized, not on purpose).

			Linus

---
 mm/filemap.c |  156 +++++++++++++++++++++++++++----------------------
 1 file changed, 89 insertions(+), 67 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc5-mm1/mm/filemap.c
@@ -1302,6 +1302,68 @@ static int fastcall page_cache_read(stru
 
 #define MMAP_LOTSAMISS  (100)
 
+/*
+ * Synchronous readahead happens when we don't even find
+ * a page in the page cache at all.
+ */
+static void do_sync_mmap_readahead(struct vm_area_struct *vma,
+				   struct file_ra_state *ra,
+				   struct file *file,
+				   pgoff_t offset)
+{
+	unsigned long ra_pages;
+	struct address_space *mapping = file->f_mapping;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (VM_RandomReadHint(vma))
+		return;
+
+	if (VM_SequentialReadHint(vma)) {
+		page_cache_sync_readahead(mapping, ra, file, offset, 1);
+		return;
+	}
+
+	if (ra->mmap_miss < INT_MAX)
+		ra->mmap_miss++;
+
+	/*
+	 * Do we miss much more than hit in this file? If so,
+	 * stop bothering with read-ahead. It will only hurt.
+	 */
+	if (ra->mmap_miss > MMAP_LOTSAMISS)
+		return;
+
+	ra_pages = max_sane_readahead(ra->ra_pages);
+	if (ra_pages) {
+		pgoff_t start = 0;
+
+		if (offset > ra_pages / 2)
+			start = offset - ra_pages / 2;
+		do_page_cache_readahead(mapping, file, start, ra_pages);
+	}
+}
+
+/*
+ * Asynchronous readahead happens when we find the page and PG_readahead,
+ * so we want to possibly extend the readahead further..
+ */
+static void do_async_mmap_readahead(struct vm_area_struct *vma,
+				    struct file_ra_state *ra,
+				    struct file *file,
+				    struct page *page,
+				    pgoff_t offset)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (VM_RandomReadHint(vma))
+		return;
+	if (ra->mmap_miss > 0)
+		ra->mmap_miss--;
+	if (PageReadahead(page))
+		page_cache_async_readahead(mapping, ra, file, page, offset, 1);
+}
+
 /**
  * filemap_fault - read in file data for page fault handling
  * @vma:	vma in which the fault was taken
@@ -1321,78 +1383,44 @@ int filemap_fault(struct vm_area_struct 
 	struct address_space *mapping = file->f_mapping;
 	struct file_ra_state *ra = &file->f_ra;
 	struct inode *inode = mapping->host;
+	pgoff_t offset = vmf->pgoff;
 	struct page *page;
 	unsigned long size;
-	int did_readaround = 0;
 	int ret = 0;
 
 	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-	if (vmf->pgoff >= size)
+	if (offset >= size)
 		return VM_FAULT_SIGBUS;
 
-	/* If we don't want any read-ahead, don't bother */
-	if (VM_RandomReadHint(vma))
-		goto no_cached_page;
-
 	/*
 	 * Do we have something in the page cache already?
 	 */
-retry_find:
-	page = find_lock_page(mapping, vmf->pgoff);
-	/*
-	 * For sequential accesses, we use the generic readahead logic.
-	 */
-	if (VM_SequentialReadHint(vma)) {
-		if (!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_async_readahead(mapping, ra, file, page,
-							   vmf->pgoff, 1);
-		}
-	}
-
-	if (!page) {
-		unsigned long ra_pages;
-
-		ra->mmap_miss++;
-
+	page = find_get_page(mapping, offset);
+	if (likely(page)) {
 		/*
-		 * Do we miss much more than hit in this file? If so,
-		 * stop bothering with read-ahead. It will only hurt.
+		 * We found the page, so try async readahead before
+		 * waiting for the lock.
 		 */
-		if (ra->mmap_miss > MMAP_LOTSAMISS)
-			goto no_cached_page;
+		do_async_mmap_readahead(vma, ra, file, page, offset);
+		lock_page(page);
 
-		/*
-		 * To keep the pgmajfault counter straight, we need to
-		 * check did_readaround, as this is an inner loop.
-		 */
-		if (!did_readaround) {
-			ret = VM_FAULT_MAJOR;
-			count_vm_event(PGMAJFAULT);
-		}
-		did_readaround = 1;
-		ra_pages = max_sane_readahead(file->f_ra.ra_pages);
-		if (ra_pages) {
-			pgoff_t start = 0;
-
-			if (vmf->pgoff > ra_pages / 2)
-				start = vmf->pgoff - ra_pages / 2;
-			do_page_cache_readahead(mapping, file, start, ra_pages);
+		/* Did it get truncated? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			put_page(page);
+			goto no_cached_page;
 		}
-		page = find_lock_page(mapping, vmf->pgoff);
+	} else {
+		/* No page in the page cache at all */
+		do_sync_mmap_readahead(vma, ra, file, offset);
+		ret = VM_FAULT_MAJOR;
+		count_vm_event(PGMAJFAULT);
+retry_find:
+		page = find_lock_page(mapping, offset);
 		if (!page)
 			goto no_cached_page;
 	}
 
-	if (!did_readaround)
-		ra->mmap_miss--;
-
 	/*
 	 * We have a locked page in the page cache, now we need to check
 	 * that it's up-to-date. If not, it is going to be due to an error.
@@ -1400,19 +1428,19 @@ retry_find:
 	if (unlikely(!PageUptodate(page)))
 		goto page_not_uptodate;
 
-	/* Must recheck i_size under page lock */
+	/*
+	 * Found the page and have a reference on it.
+	 * We must recheck i_size under page lock
+	 */
 	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-	if (unlikely(vmf->pgoff >= size)) {
+	if (unlikely(offset >= size)) {
 		unlock_page(page);
 		page_cache_release(page);
 		return VM_FAULT_SIGBUS;
 	}
 
-	/*
-	 * Found the page and have a reference on it.
-	 */
 	mark_page_accessed(page);
-	ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
+	ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT;
 	vmf->page = page;
 	return ret | VM_FAULT_LOCKED;
 
@@ -1421,7 +1449,7 @@ no_cached_page:
 	 * We're only likely to ever get here if MADV_RANDOM is in
 	 * effect.
 	 */
-	error = page_cache_read(file, vmf->pgoff);
+	error = page_cache_read(file, offset);
 
 	/*
 	 * The page we want has now been added to the page cache.
@@ -1441,12 +1469,6 @@ no_cached_page:
 	return VM_FAULT_SIGBUS;
 
 page_not_uptodate:
-	/* IO error path */
-	if (!did_readaround) {
-		ret = VM_FAULT_MAJOR;
-		count_vm_event(PGMAJFAULT);
-	}
-
 	/*
 	 * Umm, take care of errors if the page isn't up-to-date.
 	 * Try to re-read it _once_. We do this synchronously,

-- 

[PATCH 3/9] readahead: auto detection of sequential mmap reads

[Fengguang Wu]

[-- Attachment #1: readahead-auto-detect-mmap-sequential-reads.patch --]
[-- Type: text/plain, Size: 2138 bytes --]

Auto-detect sequential mmap reads and do sync/async readahead for them.

The sequential mmap readahead will be triggered when
- sync readahead: it's a major fault and (prev_offset==offset-1);
- async readahead: minor fault on PG_readahead page with valid readahead state.

It's a bit conservative to require valid readahead state for async readahead,
which means we don't do readahead for interleaved reads for now, but let's make
it safe for this initial try.

======
The benefits of doing readahead instead of read-around:
- less I/O wait thanks to async readahead
- double real I/O size and no more cache hits

Some numbers on 100,000 sequential mmap reads:

                                    user       system    cpu        total
(1-1)  plain -mm, 128KB readaround: 3.224      2.554     48.40%     11.838
(1-2)  plain -mm, 256KB readaround: 3.170      2.392     46.20%     11.976
(2)  patched -mm, 128KB readahead:  3.117      2.448     47.33%     11.607

The patched (2) has smallest total time. It has no cache hit overheads
and less I/O block time(thanks to async readahead). Here the I/O size
makes no much difference, since there's only one single stream.

Note that (1-1)'s real I/O size is 64KB and (1-2)'s real I/O size is
128KB, since the half of the read-around pages will be cache hits.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

---
 mm/filemap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc5-mm1/mm/filemap.c
@@ -1318,7 +1318,8 @@ static void do_sync_mmap_readahead(struc
 	if (VM_RandomReadHint(vma))
 		return;
 
-	if (VM_SequentialReadHint(vma)) {
+	if (VM_SequentialReadHint(vma) ||
+			offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
 		page_cache_sync_readahead(mapping, ra, file, offset, 1);
 		return;
 	}
@@ -1360,7 +1361,8 @@ static void do_async_mmap_readahead(stru
 		return;
 	if (ra->mmap_miss > 0)
 		ra->mmap_miss--;
-	if (PageReadahead(page))
+	if (PageReadahead(page) &&
+			offset == ra->start + ra->size - ra->async_size)
 		page_cache_async_readahead(mapping, ra, file, page, offset, 1);
 }
 

-- 

[PATCH 4/9] readahead: quick startup on sequential mmap readahead

[Fengguang Wu]

[-- Attachment #1: readahead-sequential-quick-start.patch --]
[-- Type: text/plain, Size: 851 bytes --]

When the user explicitly sets MADV_SEQUENTIAL, we should really avoid the slow
readahead size ramp-up phase and start full-size readahead immediately.

This patch won't change behavior for the auto-detected sequential mmap reads.
Its previous read-around size is ra_pages/2, so it will be doubled to the full
readahead size anyway.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/filemap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-2.6.24-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc5-mm1/mm/filemap.c
@@ -1320,7 +1320,7 @@ static void do_sync_mmap_readahead(struc
 
 	if (VM_SequentialReadHint(vma) ||
 			offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
-		page_cache_sync_readahead(mapping, ra, file, offset, 1);
+		page_cache_sync_readahead(mapping, ra, file, offset, ra->ra_pages);
 		return;
 	}
 

-- 

[PATCH 5/9] readahead: make ra_submit() non-static

[Fengguang Wu]

[-- Attachment #1: readahead-export-ra_submit.patch --]
[-- Type: text/plain, Size: 1086 bytes --]

Make ra_submit() non-static and callable from other files.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
---
 include/linux/mm.h |    3 +++
 mm/readahead.c     |    2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

--- linux-2.6.24-rc5-mm1.orig/include/linux/mm.h
+++ linux-2.6.24-rc5-mm1/include/linux/mm.h
@@ -1103,6 +1103,9 @@ void page_cache_async_readahead(struct a
 				unsigned long size);
 
 unsigned long max_sane_readahead(unsigned long nr);
+unsigned long ra_submit(struct file_ra_state *ra,
+		        struct address_space *mapping,
+			struct file *filp);
 
 /* Do stack extension */
 extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc5-mm1/mm/readahead.c
@@ -242,7 +242,7 @@ subsys_initcall(readahead_init);
 /*
  * Submit IO for the read-ahead request in file_ra_state.
  */
-static unsigned long ra_submit(struct file_ra_state *ra,
+unsigned long ra_submit(struct file_ra_state *ra,
 		       struct address_space *mapping, struct file *filp)
 {
 	int actual;

-- 

[PATCH 6/9] readahead: save mmap read-around states in file_ra_state

[Fengguang Wu]

[-- Attachment #1: readahead-convert-mmap-readaround.patch --]
[-- Type: text/plain, Size: 825 bytes --]

Change mmap read-around to share the same code style and data structure
with readahead code.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/filemap.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc5-mm1/mm/filemap.c
@@ -1334,13 +1334,15 @@ static void do_sync_mmap_readahead(struc
 	if (ra->mmap_miss > MMAP_LOTSAMISS)
 		return;
 
+	/*
+	 * mmap read-around
+	 */
 	ra_pages = max_sane_readahead(ra->ra_pages);
 	if (ra_pages) {
-		pgoff_t start = 0;
-
-		if (offset > ra_pages / 2)
-			start = offset - ra_pages / 2;
-		do_page_cache_readahead(mapping, file, start, ra_pages);
+		ra->start = max_t(long, 0, offset - ra_pages / 2);
+		ra->size = ra_pages;
+		ra->async_size = 0;
+		ra_submit(ra, mapping, file);
 	}
 }
 

-- 

[PATCH 7/9] readahead: remove unused do_page_cache_readahead()

[Fengguang Wu]

[-- Attachment #1: readahead-remove-do_page_cache_readahead.patch --]
[-- Type: text/plain, Size: 1799 bytes --]

Remove do_page_cache_readahead().
Its last user, mmap read-around, has been changed to call ra_submit().

Also, the no-readahead-if-congested logic is not appropriate here. 
Raw 1-page reads can only makes things painfully slower, and
users are pretty sensitive about the slow loading of executables.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 include/linux/mm.h |    2 --
 mm/readahead.c     |   16 ----------------
 2 files changed, 18 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/include/linux/mm.h
+++ linux-2.6.24-rc5-mm1/include/linux/mm.h
@@ -1084,8 +1084,6 @@ int write_one_page(struct page *page, in
 #define VM_MAX_READAHEAD	128	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
 
-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);
 
--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc5-mm1/mm/readahead.c
@@ -208,22 +208,6 @@ int force_page_cache_readahead(struct ad
 }
 
 /*
- * This version skips the IO if the queue is read-congested, and will tell the
- * block layer to abandon the readahead if request allocation would block.
- *
- * force_page_cache_readahead() will ignore queue congestion and will block on
- * request queues.
- */
-int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
-			pgoff_t offset, unsigned long nr_to_read)
-{
-	if (bdi_read_congested(mapping->backing_dev_info))
-		return -1;
-
-	return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
-}
-
-/*
  * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
  * sensible upper limit.
  */

-- 

[PATCH 8/9] readahead: move max_sane_readahead() calls into force_page_cache_readahead()

[Fengguang Wu]

[-- Attachment #1: readahead-check-max_sane_readahead.patch --]
[-- Type: text/plain, Size: 1729 bytes --]

Simplify code by moving max_sane_readahead() calls into
force_page_cache_readahead().

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/fadvise.c   |    2 +-
 mm/filemap.c   |    3 +--
 mm/madvise.c   |    3 +--
 mm/readahead.c |    1 +
 4 files changed, 4 insertions(+), 5 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/mm/fadvise.c
+++ linux-2.6.24-rc5-mm1/mm/fadvise.c
@@ -89,7 +89,7 @@ asmlinkage long sys_fadvise64_64(int fd,
 		
 		ret = force_page_cache_readahead(mapping, file,
 				start_index,
-				max_sane_readahead(nrpages));
+				nrpages);
 		if (ret > 0)
 			ret = 0;
 		break;
--- linux-2.6.24-rc5-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc5-mm1/mm/filemap.c
@@ -1242,8 +1242,7 @@ do_readahead(struct address_space *mappi
 	if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
 		return -EINVAL;
 
-	force_page_cache_readahead(mapping, filp, index,
-					max_sane_readahead(nr));
+	force_page_cache_readahead(mapping, filp, index, nr);
 	return 0;
 }
 
--- linux-2.6.24-rc5-mm1.orig/mm/madvise.c
+++ linux-2.6.24-rc5-mm1/mm/madvise.c
@@ -123,8 +123,7 @@ static long madvise_willneed(struct vm_a
 		end = vma->vm_end;
 	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
-	force_page_cache_readahead(file->f_mapping,
-			file, start, max_sane_readahead(end - start));
+	force_page_cache_readahead(file->f_mapping, file, start, end - start);
 	return 0;
 }
 
--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc5-mm1/mm/readahead.c
@@ -187,6 +187,7 @@ int force_page_cache_readahead(struct ad
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
 		return -EINVAL;
 
+	nr_to_read = max_sane_readahead(nr_to_read);
 	while (nr_to_read) {
 		int err;
 

-- 

[PATCH 9/9] readahead: call max_sane_readahead() in ondemand_readahead()

[Fengguang Wu]

[-- Attachment #1: readahead-check-max_sane_readahead2.patch --]
[-- Type: text/plain, Size: 747 bytes --]

Apply the max_sane_readahead() limit in ondemand_readahead().
Just in case someone aggressively set a huge readahead size.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/readahead.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc5-mm1/mm/readahead.c
@@ -324,9 +324,9 @@ ondemand_readahead(struct address_space 
 		   bool hit_readahead_marker, pgoff_t offset,
 		   unsigned long req_size)
 {
-	int	max = ra->ra_pages;	/* max readahead pages */
 	pgoff_t prev_offset;
-	int	sequential;
+	int sequential;
+	int max = max_sane_readahead(ra->ra_pages);  /* max readahead pages */
 
 	/*
 	 * It's the expected callback offset, assume sequential access.

-- 

[PATCH 8/9] readahead: move max_sane_readahead() calls into force_page_cache_readahead()

[Fengguang Wu]

[-- Attachment #1: readahead-check-max_sane_readahead.patch --]
[-- Type: text/plain, Size: 1729 bytes --]

Simplify code by moving max_sane_readahead() calls into
force_page_cache_readahead().

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/fadvise.c   |    2 +-
 mm/filemap.c   |    3 +--
 mm/madvise.c   |    3 +--
 mm/readahead.c |    1 +
 4 files changed, 4 insertions(+), 5 deletions(-)

--- linux-2.6.24-rc4-mm1.orig/mm/fadvise.c
+++ linux-2.6.24-rc4-mm1/mm/fadvise.c
@@ -89,7 +89,7 @@ asmlinkage long sys_fadvise64_64(int fd,
 		
 		ret = force_page_cache_readahead(mapping, file,
 				start_index,
-				max_sane_readahead(nrpages));
+				nrpages);
 		if (ret > 0)
 			ret = 0;
 		break;
--- linux-2.6.24-rc4-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc4-mm1/mm/filemap.c
@@ -1242,8 +1242,7 @@ do_readahead(struct address_space *mappi
 	if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
 		return -EINVAL;
 
-	force_page_cache_readahead(mapping, filp, index,
-					max_sane_readahead(nr));
+	force_page_cache_readahead(mapping, filp, index, nr);
 	return 0;
 }
 
--- linux-2.6.24-rc4-mm1.orig/mm/madvise.c
+++ linux-2.6.24-rc4-mm1/mm/madvise.c
@@ -123,8 +123,7 @@ static long madvise_willneed(struct vm_a
 		end = vma->vm_end;
 	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
-	force_page_cache_readahead(file->f_mapping,
-			file, start, max_sane_readahead(end - start));
+	force_page_cache_readahead(file->f_mapping, file, start, end - start);
 	return 0;
 }
 
--- linux-2.6.24-rc4-mm1.orig/mm/readahead.c
+++ linux-2.6.24-rc4-mm1/mm/readahead.c
@@ -187,6 +187,7 @@ int force_page_cache_readahead(struct ad
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
 		return -EINVAL;
 
+	nr_to_read = max_sane_readahead(nr_to_read);
 	while (nr_to_read) {
 		int err;
 

--