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

[Rafael J. Wysocki]

On Monday 04 May 2009, Pavel Machek wrote:
> 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@xxxxxxx>
> > > > 
> > > > 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@xxxxxxx>
> > > > ---
> > > >  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.

But we're going to free it anyway?

Rafael
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