Hi,


* On Sat, Sep 22, 2012 at 08:42:50PM +0800, Fengguang Wu [off-list ref] wrote:

On Sat, Sep 22, 2012 at 04:03:13PM +0530, raghu.prabhu13@gmail.com wrote:

quoted

From: Raghavendra D Prabhu <redacted>

page_cache_sync_readahead checks for ra->ra_pages again, so moving the check
after VM_SequentialReadHint.

Well it depends on what case you are optimizing for. I suspect there
are much more tmpfs users than VM_SequentialReadHint users. So this
change is actually not desirable wrt the more widely used cases.

Yes, that is true. However, it was meant to eliminate duplicate 
checking of the same condition in two places. But you are right, 
it may impose overhead for majority of the cases (assuming 
POSIX_FADVISE is used less than tmpfs).

Thanks,
Fengguang

quoted

Signed-off-by: Raghavendra D Prabhu <redacted>
---
 mm/filemap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 3843445..606a648 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c

@@ -1523,8 +1523,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
 	/* If we don't want any read-ahead, don't bother */
 	if (VM_RandomReadHint(vma))
 		return;
-	if (!ra->ra_pages)
-		return;

 	if (VM_SequentialReadHint(vma)) {
 		page_cache_sync_readahead(mapping, ra, file, offset,

@@ -1532,6 +1530,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
 		return;
 	}

+	if (!ra->ra_pages)
+		return;
+
 	/* Avoid banging the cache line if not needed */
 	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
 		ra->mmap_miss++;
--

1.7.12.1

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Regards,
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Raghavendra Prabhu
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