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authorJan Kara <jack@suse.cz>2011-07-01 13:31:25 -0600
committerWu Fengguang <fengguang.wu@intel.com>2011-07-24 10:51:52 +0800
commitbcff25fc8aa47a13faff8b4b992589813f7b450a (patch)
treeae93e2b8ba1417bf6327f79154c69b9afc8328bb /mm/backing-dev.c
parentfcc5c22218a18509a7412bf074fc9a7a5d874a8a (diff)
mm: properly reflect task dirty limits in dirty_exceeded logic
We set bdi->dirty_exceeded (and thus ratelimiting code starts to call balance_dirty_pages() every 8 pages) when a per-bdi limit is exceeded or global limit is exceeded. But per-bdi limit also depends on the task. Thus different tasks reach the limit on that bdi at different levels of dirty pages. The result is that with current code bdi->dirty_exceeded ping-ponged between 1 and 0 depending on which task just got into balance_dirty_pages(). We fix the issue by clearing bdi->dirty_exceeded only when per-bdi amount of dirty pages drops below the threshold (7/8 * bdi_dirty_limit) where task limits already do not have any influence. Impact: The end result is, the dirty pages are kept more tightly under control, with the average number slightly lowered than before. This reduces the risk to throttle light dirtiers and hence more responsive. However it may add overheads by enforcing balance_dirty_pages() calls on every 8 pages when there are 2+ heavy dirtiers. CC: Andrew Morton <akpm@linux-foundation.org> CC: Christoph Hellwig <hch@infradead.org> CC: Dave Chinner <david@fromorbit.com> CC: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
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