linux-kernel - RE: MIGRATE_RESERVE pages in show

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Message-ID: <35FD53F367049845BC99AC72306C23D1029A27656A2C@CNBJMBX05.corpusers.net>
Date:	Tue, 3 Jun 2014 14:43:13 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Vlastimil Babka' <vbabka@...e.cz>
CC:	"'akpm@...ux-foundation.org'" <akpm@...ux-foundation.org>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'cody@...ux.vnet.ibm.com'" <cody@...ux.vnet.ibm.com>,
	"'linux-arch-owner@...r.kernel.org'" 
	<linux-arch-owner@...r.kernel.org>,
	'Will Deacon' <will.deacon@....com>,
	"'hannes@...xchg.org'" <hannes@...xchg.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: RE: MIGRATE_RESERVE  pages in show_mem function problems

Hi 

I see,
Your patch should be ok to fix this problem,
Could I know if this patch will be merged into kernel mainline branch?

Thanks

-----Original Message-----
From: Vlastimil Babka [mailto:vbabka@...e.cz] 
Sent: Friday, May 30, 2014 10:59 PM
To: Wang, Yalin
Cc: 'akpm@...ux-foundation.org'; 'linux-mm@...ck.org'; 'linux-kernel@...r.kernel.org'; 'cody@...ux.vnet.ibm.com'; 'linux-arch-owner@...r.kernel.org'; 'Will Deacon'; 'hannes@...xchg.org'; Joonsoo Kim
Subject: Re: MIGRATE_RESERVE pages in show_mem function problems

On 05/28/2014 04:24 AM, Wang, Yalin wrote:
> Hi
>
> I find the show_mem function show page MIGRATE types result is not 
> correct for MIGRATE_RESERVE pages :
>
> Normal: 1582*4kB (UEMC) 1317*8kB (UEMC) 1020*16kB (UEMC) 450*32kB 
> (UEMC) 206*64kB (UEMC) 40*128kB (UM) 10*256kB (UM) 10*512kB (UM) 
> 1*1024kB (M) 0*2048kB 0*4096kB = 74592kB
>
> Some pages should be marked (R)  , while it is changed into 
> MIGRATE_MOVEABLE or UNMOVEABLE in free_area list , It's not correct for debug .
> I make a patch for this:
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5dba293..6ef8ebe 
> 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1198,7 +1198,8 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>                          list_add_tail(&page->lru, list);
>                  if (IS_ENABLED(CONFIG_CMA)) {
>                          mt = get_pageblock_migratetype(page);
> -                       if (!is_migrate_cma(mt) && !is_migrate_isolate(mt))
> +                       if (!is_migrate_cma(mt) && !is_migrate_isolate(mt)
> +                               && mt != MIGRATE_RESERVE)
>                                  mt = migratetype;
>                  }
>                  set_freepage_migratetype(page, mt);
>
>
> seems work ok , I am curious is it a BUG ? or designed like this for some reason ?

Hi, this is a known problem that should be fixed for the rmqueue_bulk() part by this patch:
http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-prevent-migrate_reserve-pages-from-being-misplaced.patch

Testing is welcome if you can reproduce it easily enough.

Note that even with the patch, MIGRATE_RESERVE pageblocks can still disappear for two reasons:

- when MAX_ORDER-1 > pageblock_order (such as x86_64), there can be a single MIGRATE_RESERVE pageblock created for a smaller zone, and get merged with !MIGRATE_RESERVE buddy pageblock
- when min_free_kbytes sysctl is used, creation of new MIGRATE_RESERVE pageblocks can race with other CPUs putting pages in their pcplists, and then freeing then on a wronge free_list. If try_to_steal_freepages happens to find such misplaced page, it might remark the pageblock.

I think the second problem is extremely rare, but Joonsoo Kim confirmed the first one to happen. You can check the -mm archives for threads around the patch above.

Vlastimil

> Thanks
>
>
> <6>[  250.751554] lowmem_reserve[]: 0 0 0 <6>[  250.751606] Normal: 
> 1582*4kB (UEMC) 1317*8kB (UEMC) 1020*16kB (UEMC) 450*32kB (UEMC) 
> 206*64kB (UEMC) 40*128kB (UM) 10*256kB (UM) 10*512kB (UM) 1*1024kB (M) 
> 0*2048kB 0*4096kB = 74592kB <6>[  250.751848] HighMem: 167*4kB (UC) 
> 3*8kB (U) 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 
> 0*2048kB 0*4096kB = 692kB <6>[  250.752020] 62596 total pagecache 
> pages <6>[  250.752046] 0 pages in swap cache <6>[  250.752074] Swap 
> cache stats: add 0, delete 0, find 0/0
>
>
>
>
> Sony Mobile Communications
> Tel: My Number +18610323092
> yalin.wang@...ymobile.com
> sonymobile.com
>
>
>
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