* On Sun, Jul 10, 2011 at 08:59:06AM -0700, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
On Sun, Jul 10, 2011 at 08:59:09PM +0800, Raghavendra D Prabhu wrote:
* On Sat, Jul 09, 2011 at 01:53:08PM -0700, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
>On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
>>page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.
>NAK. This patch adds nothing but overheads.
>>--- a/mm/filemap.c
>>+++ b/mm/filemap.c
>>@@ -1566,8 +1566,6 @@ 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,
>>@@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>> return;
>> }
>>+ if (!ra->ra_pages)
>>+ return;
>>+
>page_cache_sync_readahead() has the same
> if (!ra->ra_pages)
> return;
1. Yes, I saw that and that is why I moved it after the condition, so that duplicate checks are
not needed -- ie., if VM_SequentialReadHint is true, then
(!ra->ra_pages) is checked twice otherwise.
Ok, I see.
2. Also, another thought, is the check needed at its original place (if
not it can be removed), reasons being -- filesystems like tmpfs which
have ra_pages set to 0 don't use filemap_fault in their VMA ops and also
Good point. tmpfs is using shmem_fault().. Can you remove the test?
I have removed that test. Patch attached.
do_sync_mmap_readahead is called in a major page fault context.
Right. This is irrelevant however, because if pa_pages==0, the
page faults will normally be major ones.
Thanks,
Fengguang
>So the patch adds the call into page_cache_sync_readahead() just to return..
>Thanks,
>Fengguang
--------------------------
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net
======================================================================
The check for ra->ra_pages is not required since fs like tmpfs which have
ra_pages set to 0 don't use filemap_fault as part of their VMA ops (it uses
shmem_fault). Also, page_cache_sync_readahead does its own check for ra_pages.
Signed-off-by: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx>
---
mm/filemap.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 074c23d..0bcd276 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1566,8 +1566,6 @@ 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,
--
1.7.6
--------------------------
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net
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