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Date: Thu, 19 Jan 2006 18:27:18 -0800
From: Andrew Morton <akpm@osdl.org>
To: Christoph Lameter <clameter@engr.sgi.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] shrink_list: Use of && instead || leads to unintended
 writing of pages
Message-Id: <20060119182718.575bd08a.akpm@osdl.org>
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Christoph Lameter <clameter@engr.sgi.com> wrote:
>
> [PATCH] Implement sane function of sc->may_writepage
> 
>  Make sc->may_writepage control the writeout behavior of shrink_list.
> 
>  Remove the laptop_mode trick from shrink_list and instead set may_writepage in
>  try_to_free_pages properly.
> 
>  Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
>  Index: linux-2.6.16-rc1-mm1/mm/vmscan.c
>  ===================================================================
>  --- linux-2.6.16-rc1-mm1.orig/mm/vmscan.c	2006-01-19 15:50:19.000000000 -0800
>  +++ linux-2.6.16-rc1-mm1/mm/vmscan.c	2006-01-19 17:42:07.000000000 -0800
>  @@ -491,7 +491,7 @@ static int shrink_list(struct list_head 
>   				goto keep_locked;
>   			if (!may_enter_fs)
>   				goto keep_locked;
>  -			if (laptop_mode && !sc->may_writepage)
>  +			if (!sc->may_writepage)
>   				goto keep_locked;
>   
>   			/* Page is dirty, try to write it out here */
>  @@ -1409,7 +1409,7 @@ int try_to_free_pages(struct zone **zone
>   	int i;
>   
>   	sc.gfp_mask = gfp_mask;
>  -	sc.may_writepage = 0;
>  +	sc.may_writepage = !laptop_mode;
>   	sc.may_swap = 1;
>   
>   	inc_page_state(allocstall);
>  @@ -1512,7 +1512,7 @@ loop_again:
>   	total_scanned = 0;
>   	total_reclaimed = 0;
>   	sc.gfp_mask = GFP_KERNEL;
>  -	sc.may_writepage = 0;
>  +	sc.may_writepage = 1;
>   	sc.may_swap = 1;
>   	sc.nr_mapped = read_page_state(nr_mapped);

The balance_pgdat() change is wrong, surely?  We want !laptop_mode.