* 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. 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 do_sync_mmap_readahead is called in a major page fault context.
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
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