linux-kernel - Re: [PATCH] vmscan: skip freeing memory from zones with lots free

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Message-Id: <20081129122901.6243d2fa.akpm@linux-foundation.org>
Date:	Sat, 29 Nov 2008 12:29:01 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH] vmscan: skip freeing memory from zones with lots free

On Sat, 29 Nov 2008 13:59:21 -0500 Rik van Riel <riel@...hat.com> wrote:

> Andrew Morton wrote:
> > On Sat, 29 Nov 2008 13:41:34 -0500 Rik van Riel <riel@...hat.com> wrote:
> > 
> >> Andrew Morton wrote:
> >>> On Sat, 29 Nov 2008 12:58:32 -0500 Rik van Riel <riel@...hat.com> wrote:
> >>>
> >>>>> Will this new patch reintroduce the problem which
> >>>>> 26e4931632352e3c95a61edac22d12ebb72038fe fixed?
> >> No, that problem is already taken care of by the fact that
> >> active pages always get deactivated in the current VM,
> >> regardless of whether or not they were referenced.
> > 
> > err, sorry, that was the wrong commit. 
> > 26e4931632352e3c95a61edac22d12ebb72038fe _introduced_ the problem, as
> > predicted in the changelog.
> > 
> > 265b2b8cac1774f5f30c88e0ab8d0bcf794ef7b3 later fixed it up.
> 
> The patch I sent in this thread does not do any baling out,
> it only skips zones where the number of free pages is more
> than 4 times zone->pages_high.

But that will have the same effect as baling out.  Moreso, in fact.

> Equal pressure is still applied to the other zones.
> 
> This should not be a problem since we do not enter direct
> reclaim unless the free pages in every zone in our zonelist
> are below zone->pages_low.
> 
> Zone skipping is only done by tasks that have been in the
> direct reclaim code for a long time.

>From 265b2b8cac1774f5f30c88e0ab8d0bcf794ef7b3:

    We currently have a problem with the balancing of reclaim
    between zones: much more reclaim happens against highmem than
    against lowmem.

This problem will be reintroduced, will it not?
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