linux-kernel - Re: [PATCH] mm: fix a regression with HIGHMEM introduced by changeset 7f1290f2f2a4d

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Date:	Tue, 06 Nov 2012 10:23:40 +0000
From:	Chris Clayton <chris2553@...glemail.com>
To:	Jiang Liu <jiang.liu@...wei.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Jianguo Wu <wujianguo@...wei.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix a regression with HIGHMEM introduced by changeset
 7f1290f2f2a4d



On 11/06/12 01:31, Jiang Liu wrote:
> Changeset 7f1290f2f2 tries to fix a issue when calculating
> zone->present_pages, but it causes a regression to 32bit systems with
> HIGHMEM. With that changeset, function reset_zone_present_pages()
> resets all zone->present_pages to zero, and fixup_zone_present_pages()
> is called to recalculate zone->present_pages when boot allocator frees
> core memory pages into buddy allocator. Because highmem pages are not
> freed by bootmem allocator, all highmem zones' present_pages becomes
> zero.
>
> Actually there's no need to recalculate present_pages for highmem zone
> because bootmem allocator never allocates pages from them. So fix the
> regression by skipping highmem in function reset_zone_present_pages()
> and fixup_zone_present_pages().
>
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> Signed-off-by: Jianguo Wu <wujianguo@...wei.com>
> Reported-by: Maciej Rutecki <maciej.rutecki@...il.com>
> Tested-by: Maciej Rutecki <maciej.rutecki@...il.com>
> Cc: Chris Clayton <chris2553@...glemail.com>
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
>
> ---
>
> Hi Maciej,
> 	Thanks for reporting and bisecting. We have analyzed the regression
> and worked out a patch for it. Could you please help to verify whether it
> fix the regression?
> 	Thanks!
> 	Gerry
>

Thanks Gerry.

I've applied this patch to 3.7.0-rc4 and can confirm that it fixes the 
problem I had with my laptop failing to resume after a suspend to disk.

Tested-by: Chris Clayton <chris2553@...glemail.com>

> ---
>   mm/page_alloc.c |    8 +++++---
>   1 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b74de6..2311f15 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6108,7 +6108,8 @@ void reset_zone_present_pages(void)
>   	for_each_node_state(nid, N_HIGH_MEMORY) {
>   		for (i = 0; i < MAX_NR_ZONES; i++) {
>   			z = NODE_DATA(nid)->node_zones + i;
> -			z->present_pages = 0;
> +			if (!is_highmem(z))
> +				z->present_pages = 0;
>   		}
>   	}
>   }
> @@ -6123,10 +6124,11 @@ void fixup_zone_present_pages(int nid, unsigned long start_pfn,
>
>   	for (i = 0; i < MAX_NR_ZONES; i++) {
>   		z = NODE_DATA(nid)->node_zones + i;
> +		if (is_highmem(z))
> +			continue;
> +
>   		zone_start_pfn = z->zone_start_pfn;
>   		zone_end_pfn = zone_start_pfn + z->spanned_pages;
> -
> -		/* if the two regions intersect */
>   		if (!(zone_start_pfn >= end_pfn	|| zone_end_pfn <= start_pfn))
>   			z->present_pages += min(end_pfn, zone_end_pfn) -
>   					    max(start_pfn, zone_start_pfn);
>
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