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

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Date:	Sun, 3 May 2009 19:51:27 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 3/4] PM/Hibernate: Use memory allocations to free
	memory (rev. 2)

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?

Thanks,
Fengguang
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