Messages in this thread Patch in this message | | | Date | Tue, 26 Apr 2011 17:43:53 +0800 | From | Wu Fengguang <> | Subject | [PATCH 1/3] readahead: return early when readahead is disabled |
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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).
Tested-by: Tim Chen <tim.c.chen@intel.com> Reported-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> --- mm/filemap.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- linux-next.orig/mm/filemap.c 2011-04-23 08:56:59.000000000 +0800 +++ linux-next/mm/filemap.c 2011-04-23 09:01:44.000000000 +0800 @@ -1528,6 +1528,8 @@ static void do_sync_mmap_readahead(struc /* 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)) { @@ -1550,12 +1552,10 @@ static void do_sync_mmap_readahead(struc * 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); } /*
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