Messages in this thread | | | Date | Fri, 14 Mar 2014 12:06:25 -0400 | From | Rik van Riel <> | Subject | Re: [patch] mm: vmscan: do not swap anon pages just because free+file is low |
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On 03/14/2014 11:35 AM, Johannes Weiner wrote: > Page reclaim force-scans / swaps anonymous pages when file cache drops > below the high watermark of a zone in order to prevent what little > cache remains from thrashing. > > However, on bigger machines the high watermark value can be quite > large and when the workload is dominated by a static anonymous/shmem > set, the file set might just be a small window of used-once cache. In > such situations, the VM starts swapping heavily when instead it should > be recycling the no longer used cache. > > This is a longer-standing problem, but it's more likely to trigger > after 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") > because file pages can no longer accumulate in a single zone and are > dispersed into smaller fractions among the available zones. > > To resolve this, do not force scan anon when file pages are low but > instead rely on the scan/rotation ratios to make the right prediction.
I am not entirely sure that the scan/rotation ratio will be meaningful when the page cache has been essentially depleted, but on larger systems the distance between the low and high watermark is gigantic, and I have no better idea on how to fix the bug you encountered, so ...
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > Cc: <stable@kernel.org> [3.12+]
Reviewed-by: Rik van Riel <riel@redhat.com>
-- All rights reversed
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