lkml.org 
[lkml]   [2014]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] mm: vmscan: do not swap anon pages just because free+file is low
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


\
 
 \ /
  Last update: 2014-03-14 17:41    [W:0.187 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site