From 1b5e62b42b55c509eea04c3c0f25e42c8b35b564 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Mon, 23 Mar 2009 08:57:38 +0800 Subject: [PATCH] writeback: double the dirty thresholds Enlarge default dirty ratios from 5/10 to 10/20. This fixes [Bug #12809] iozone regression with 2.6.29-rc6. The iozone benchmarks are performed on a 1200M file, with 8GB ram. iozone -i 0 -i 1 -i 2 -i 3 -i 4 -r 4k -s 64k -s 512m -s 1200m -b tmp.xls iozone -B -r 4k -s 64k -s 512m -s 1200m -b tmp.xls The performance regression is triggered by commit 1cf6e7d83bf3(mm: task dirty accounting fix), which makes more correct/thorough dirty accounting. The default 5/10 dirty ratios were picked (a) with the old dirty logic and (b) largely at random and (c) designed to be aggressive. In particular, that (a) means that having fixed some of the dirty accounting, maybe the real bug is now that it was always too aggressive, just hidden by an accounting issue. The enlarged 10/20 dirty ratios are just about enough to fix the regression. [ We will have to look at how this affects the old fsync() latency issue, but that probably will need independent work. - Linus ] Cc: Nick Piggin Cc: Peter Zijlstra Reported-by: "Lin, Ming M" Tested-by: "Lin, Ming M" Signed-off-by: Wu Fengguang Signed-off-by: Linus Torvalds --- mm/page-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 74dc57c7434..40ca7cdb653 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -66,7 +66,7 @@ static inline long sync_writeback_pages(void) /* * Start background writeback (via pdflush) at this percentage */ -int dirty_background_ratio = 5; +int dirty_background_ratio = 10; /* * dirty_background_bytes starts at 0 (disabled) so that it is a function of @@ -83,7 +83,7 @@ int vm_highmem_is_dirtyable; /* * The generator of dirty data starts writeback at this percentage */ -int vm_dirty_ratio = 10; +int vm_dirty_ratio = 20; /* * vm_dirty_bytes starts at 0 (disabled) so that it is a function of -- 2.41.1