Messages in this thread Patch in this message | | | Date | Tue, 12 Jul 2011 04:32:09 +0530 | From | Raghavendra D Prabhu <> | Subject | Re. Revised [PATCH 3/3] mm/readahead: Remove the check for ra->ra_pages |
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* On Sun, Jul 10, 2011 at 08:59:06AM -0700, Wu Fengguang <fengguang.wu@intel.com> 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@intel.com> 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@wnohang.net> --- 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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