Re: [PATCH] mm: consider all swapped back pages in used-once logic

[Andrew Morton]

On Thu, 17 May 2012 11:13:53 +0200 Michal Hocko <mhocko@xxxxxxx> wrote:

> [64574746 vmscan: detect mapped file pages used only once] made mapped pages
> have another round in inactive list because they might be just short
> lived and so we could consider them again next time. This heuristic
> helps to reduce pressure on the active list with a streaming IO
> worklods.
> This patch fixes a regression introduced by this commit for heavy shmem

A performance regression, specifically.

Are you able to quantify it?

> based workloads because unlike Anon pages, which are excluded from this
> heuristic because they are usually long lived, shmem pages are handled
> as a regular page cache.
> This doesn't work quite well, unfortunately, if the workload is mostly
> backed by shmem (in memory database sitting on 80% of memory) with a
> streaming IO in the background (backup - up to 20% of memory). Anon
> inactive list is full of (dirty) shmem pages when watermarks are
> hit. Shmem pages are kept in the inactive list (they are referenced)
> in the first round and it is hard to reclaim anything else so we reach
> lower scanning priorities very quickly which leads to an excessive swap
> out.
> 
> Let's fix this by excluding all swap backed pages (they tend to be long
> lived wrt. the regular page cache anyway) from used-once heuristic and
> rather activate them if they are referenced.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/