linux-kernel - Re: [PATCH 3/3][RFC] swsusp: shrink file cache first

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Date:	Sun, 8 Feb 2009 21:56:50 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	kosaki.motohiro@...fujitsu.com, riel@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/3][RFC] swsusp: shrink file cache first

On Sat, Feb 07, 2009 at 06:23:53PM +0100, Rafael J. Wysocki wrote:
> On Saturday 07 February 2009, Johannes Weiner wrote:
> > On Fri, Feb 06, 2009 at 01:00:09PM -0800, Andrew Morton wrote:
> > > On Fri, 6 Feb 2009 05:49:07 +0100
> > > Johannes Weiner <hannes@...xchg.org> wrote:
> > > 
> > > > > and, I think you should mesure performence result.
> > > > 
> > > > Yes, I'm still thinking about ideas how to quantify it properly.  I
> > > > have not yet found a reliable way to check for whether the working set
> > > > is intact besides seeing whether the resumed applications are
> > > > responsive right away or if they first have to swap in their pages
> > > > again.
> > > 
> > > Describing your subjective non-quantitative impressions would be better
> > > than nothing...
> > 
> > Okay.
> > 
> > > The patch bugs me.
> > 
> > Please ignore it, it is broken as is.  My verbal cortex got obviously
> > disconnected from my code cortex when writing the changelog...
> 
> If I understood this correctly, patch 3/3 is to be disregarded.
> 
> > And I will reconsider the actual change bits, I still think that we
> > shouldn't scan anon page lists while may_swap is zero.
> 
> Hm, can you please remind me what may_swap == 0 acutally means?

That no mapped pages are reclaimed.  These are also mapped file pages,
but more importantly in this case, anon pages.  See this check in
shrink_page_list():

                if (!sc->may_swap && page_mapped(page))
                        goto keep_locked;

So scanning anon lists without allowing to unmap doesn't free memory.

	Hannes
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