Hi, * On Sat, Sep 22, 2012 at 08:42:50PM +0800, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
On Sat, Sep 22, 2012 at 04:03:13PM +0530, raghu.prabhu13@xxxxxxxxx wrote:From: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx> 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, FengguangSigned-off-by: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
Regards, -- Raghavendra Prabhu GPG Id : 0xD72BE977 Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977 www: wnohang.net
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