linux-kernel - [PATCH 0/5] PM: Drop shrink_all

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Date:	Mon, 4 May 2009 02:08:41 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Wu Fengguang <fengguang.wu@...el.com>,
	linux-pm@...ts.linux-foundation.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>, pavel@....cz,
	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org
Subject: [PATCH 0/5] PM: Drop shrink_all_memory (rev. 3)

On Sunday 03 May 2009, Rafael J. Wysocki wrote:
> On Sunday 03 May 2009, Wu Fengguang wrote:
> > 
> > Hi Rafael,
> 
> Hi,
> 
> > I happened to be doing some benchmarks on the older shrink_all_memory(),
> > Hopefully it can be a useful reference point for the new design.
> > 
> > The current swsusp_shrink_memory()/shrink_all_memory() are terribly
> > inefficient: it takes 7-9s to free up 1.4G memory:
> 
> One reason may be that it takes too many steps to do it,
> 
> > [  131.899389] PM: Freed 1413380 kbytes in 7.03 seconds (201.04 MB/s)
> > [  732.757916] PM: Freed 1490116 kbytes in 9.37 seconds (159.03 MB/s)
> 
> because the new way doesn't seem to do any better.
> 
> > Below are the logs I collected by injecting printks. There are
> > basically two major problems:
> > - swsusp_shrink_memory() scans the whole 2G memory again and again;
> > - shrink_all_memory() is slow. It won't reclaim pages at all with
> >   small priority values, because it's batching size is 10000 pages.
> 
> I know that swsusp_shrink_memory() has problems, that's why I'd like to get rid
> of it.
> 
> > I wonder if it's possible to free up the memory within 1s at all.
> 
> I'm not sure.
> 
> Apparently, the counting of saveable pages takes substantial time (0.5 s each
> iteration on my 64-bit test box), so we can improve that by limiting the number
> of iterations.
> 
> Well, perhaps we can do it all in one shot after all, I'll think how to do that.

I've changed swsusp_shrink_memory() to preallocate all of the pages in one
iteration.  Although it doesn't seem to improve the speed of memory shrinking,
the function is simpler in this form.

Anyway, updated patch series follows:

[1/5] - the Andrew's patch introducing __GFP_NO_OOM_KILL (I decided it would be
        better do it this way in this particular case.  The fact that the OOM
        killer is not going to work after tasks have been frozen is a different
        issue.)

[2/5] - move swsusp_shrink_memory to snapshot.c, no major changes

[3/5] - remove the shrinking of memory from suspend code (in a separate patch
         as requested by Linus)

[4/5] - use memory allocations to for making the room for the image

[5/5] - do not release all memory allocated by [4/5] and use it for
        creating the image directly (some allocated memory is released).

Thanks,
Rafael

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