From 275b12bf5486f6f531111fd3d7dbbf01df427cfe Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Tue, 24 May 2011 17:12:28 -0700 Subject: [PATCH] readahead: return early when readahead is disabled Reduce readahead overheads by returning early in do_sync_mmap_readahead(). tmpfs has ra_pages=0 and it can page fault really fast (not constraint by IO if not swapping). Signed-off-by: Wu Fengguang Tested-by: Tim Chen Reported-by: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 88354ae0b1fd..c974a2863897 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1556,6 +1556,8 @@ 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) || offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) { @@ -1578,12 +1580,10 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, * mmap read-around */ ra_pages = max_sane_readahead(ra->ra_pages); - if (ra_pages) { - ra->start = max_t(long, 0, offset - ra_pages/2); - ra->size = ra_pages; - ra->async_size = 0; - ra_submit(ra, mapping, file); - } + ra->start = max_t(long, 0, offset - ra_pages / 2); + ra->size = ra_pages; + ra->async_size = 0; + ra_submit(ra, mapping, file); } /*