linux-kernel - Re: FWD: [PATCH v2] vmscan: limit concurrent reclaimers in shrink

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Date:	Thu, 17 Dec 2009 09:43:22 -0500
From:	Rik van Riel <riel@...hat.com>
To:	lwoodman@...hat.com
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, akpm@...ux-foundation.org,
	linux-mm <linux-mm@...ck.org>
Subject: Re: FWD:  [PATCH v2] vmscan: limit concurrent reclaimers in shrink_zone

On 12/17/2009 07:23 AM, Larry Woodman wrote:

>>> The system would not respond so I dont know whats going on yet. I'll
>>> add debug code to figure out why its in that state as soon as I get
>>> access to the hardware.
>
> This was in response to Rik's first patch and seems to be fixed by the
> latest path set.
>
> Finally, having said all that, the system still struggles reclaiming
> memory with
> ~10000 processes trying at the same time, you fix one bottleneck and it
> moves
> somewhere else. The latest run showed all but one running process
> spinning in
> page_lock_anon_vma() trying for the anon_vma_lock. I noticed that there are
> ~5000 vma's linked to one anon_vma, this seems excessive!!!

I have some ideas on how to keep processes waiting better
on the per zone reclaim_wait waitqueue.

For one, we should probably only do the lots-free wakeup
if we have more than zone->pages_high free pages in the
zone - having each of the waiters free some memory one
after another should not be a problem as long as we do
not have too much free memory in the zone.

Currently it's a hair trigger, with the threshold for
processes going into the page reclaim path and processes
exiting it "plenty free" being exactly the same.

Some hysteresis there could help.

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