linux-kernel - Re: [PATCH 3/4] PM/Hibernate: Use memory allocations to free memory (rev. 2)

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Message-ID: <20090504093121.GB30306@elf.ucw.cz>
Date:	Mon, 4 May 2009 11:31:21 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 3/4] PM/Hibernate: Use memory allocations to free
	memory (rev. 2)

On Sun 2009-05-03 18:22:54, Rafael J. Wysocki wrote:
> On Sunday 03 May 2009, Wu Fengguang wrote:
> > On Sun, May 03, 2009 at 02:24:20AM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > 
> > > Modify the hibernation memory shrinking code so that it will make
> > > memory allocations to free memory instead of using an artificial
> > > memory shrinking mechanism for that.  Remove the shrinking of
> > > memory from the suspend-to-RAM code, where it is not really
> > > necessary.  Finally, remove the no longer used memory shrinking
> > > functions from mm/vmscan.c .
> > > 
> > > [rev. 2: Use the existing memory bitmaps for marking preallocated
> > >  image pages and use swsusp_free() from releasing them, introduce
> > >  GFP_IMAGE, add comments describing the memory shrinking strategy.]
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > ---
> > >  kernel/power/main.c     |   20 ------
> > >  kernel/power/snapshot.c |  132 +++++++++++++++++++++++++++++++++-----------
> > >  mm/vmscan.c             |  142 ------------------------------------------------
> > >  3 files changed, 101 insertions(+), 193 deletions(-)
> > > 
> > > Index: linux-2.6/kernel/power/snapshot.c
> > > ===================================================================
> > > --- linux-2.6.orig/kernel/power/snapshot.c
> > > +++ linux-2.6/kernel/power/snapshot.c
> > > @@ -1066,41 +1066,97 @@ void swsusp_free(void)
> > >  	buffer = NULL;
> > >  }
> > >  
> > > +/* Helper functions used for the shrinking of memory. */
> > > +
> > > +#ifdef CONFIG_HIGHMEM
> > > +#define GFP_IMAGE	(GFP_KERNEL | __GFP_HIGHMEM | __GFP_NO_OOM_KILL)
> > > +#else
> > > +#define GFP_IMAGE	(GFP_KERNEL | __GFP_NO_OOM_KILL)
> > > +#endif
> > 
> > The CONFIG_HIGHMEM test is not necessary: __GFP_HIGHMEM is always defined.
> > 
> > > +#define SHRINK_BITE	10000
> > 
> > This is ~40MB. A full scan of (for example) 8G pages will be time
> > consuming, not to mention we have to do it 2*(8G-500M)/40M = 384 times!
> > 
> > Can we make it a LONG_MAX? 
> 
> No, I don't think so.  The problem is the number of pages we'll need to copy
> is generally shrinking  as we allocate memory, so we can't do that in one shot.
> 
> We can make it a greater number, but I don't really think it would be a good
> idea to make it greater than 100 MB.

Well, even 100MB is quite big: on 128MB machine, that will probably
mean freeing all the memory (instead of "as much as needed"). And that
memory needs to go to disk, so it will be slow.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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