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From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
	Sangseok Lee <sangseok.lee@lge.com>
Subject: Re: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic
Date: Fri, 7 Oct 2016 23:30:25 +0900	[thread overview]
Message-ID: <20161007143025.GB3060@bbox> (raw)
In-Reply-To: <6bcd7066-2748-8a96-4479-f85b18765948@suse.cz>

On Fri, Oct 07, 2016 at 02:44:15PM +0200, Vlastimil Babka wrote:
> On 10/07/2016 07:45 AM, Minchan Kim wrote:
> >There is race between page freeing and unreserved highatomic.
> >
> > CPU 0				    CPU 1
> >
> >    free_hot_cold_page
> >      mt = get_pfnblock_migratetype
> 
> so here mt == MIGRATE_HIGHATOMIC?

Yes.

> 
> >      set_pcppage_migratetype(page, mt)
> >    				    unreserve_highatomic_pageblock
> >    				    spin_lock_irqsave(&zone->lock)
> >    				    move_freepages_block
> >    				    set_pageblock_migratetype(page)
> >    				    spin_unlock_irqrestore(&zone->lock)
> >      free_pcppages_bulk
> >        __free_one_page(mt) <- mt is stale
> >
> >By above race, a page on CPU 0 could go non-highorderatomic free list
> >since the pageblock's type is changed.
> >By that, unreserve logic of
> >highorderatomic can decrease reserved count on a same pageblock
> >several times and then it will make mismatch between
> >nr_reserved_highatomic and the number of reserved pageblock.
> 
> Hmm I see.
> 
> >So, this patch verifies whether the pageblock is highatomic or not
> >and decrease the count only if the pageblock is highatomic.
> 
> Yeah I guess that's the easiest solution.
> 
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks, Vlastimil.

WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Sangseok Lee <sangseok.lee@lge.com>
Subject: Re: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic
Date: Fri, 7 Oct 2016 23:30:25 +0900	[thread overview]
Message-ID: <20161007143025.GB3060@bbox> (raw)
In-Reply-To: <6bcd7066-2748-8a96-4479-f85b18765948@suse.cz>

On Fri, Oct 07, 2016 at 02:44:15PM +0200, Vlastimil Babka wrote:
> On 10/07/2016 07:45 AM, Minchan Kim wrote:
> >There is race between page freeing and unreserved highatomic.
> >
> > CPU 0				    CPU 1
> >
> >    free_hot_cold_page
> >      mt = get_pfnblock_migratetype
> 
> so here mt == MIGRATE_HIGHATOMIC?

Yes.

> 
> >      set_pcppage_migratetype(page, mt)
> >    				    unreserve_highatomic_pageblock
> >    				    spin_lock_irqsave(&zone->lock)
> >    				    move_freepages_block
> >    				    set_pageblock_migratetype(page)
> >    				    spin_unlock_irqrestore(&zone->lock)
> >      free_pcppages_bulk
> >        __free_one_page(mt) <- mt is stale
> >
> >By above race, a page on CPU 0 could go non-highorderatomic free list
> >since the pageblock's type is changed.
> >By that, unreserve logic of
> >highorderatomic can decrease reserved count on a same pageblock
> >several times and then it will make mismatch between
> >nr_reserved_highatomic and the number of reserved pageblock.
> 
> Hmm I see.
> 
> >So, this patch verifies whether the pageblock is highatomic or not
> >and decrease the count only if the pageblock is highatomic.
> 
> Yeah I guess that's the easiest solution.
> 
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks, Vlastimil.

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  reply	other threads:[~2016-10-07 14:46 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-07  5:45 [PATCH 0/4] use up highorder free pages before OOM Minchan Kim
2016-10-07  5:45 ` Minchan Kim
2016-10-07  5:45 ` [PATCH 1/4] mm: adjust reserved highatomic count Minchan Kim
2016-10-07  5:45   ` Minchan Kim
2016-10-07 12:30   ` Vlastimil Babka
2016-10-07 12:30     ` Vlastimil Babka
2016-10-07 14:29     ` Minchan Kim
2016-10-07 14:29       ` Minchan Kim
2016-10-10  6:57       ` Vlastimil Babka
2016-10-10  6:57         ` Vlastimil Babka
2016-10-11  4:19         ` Minchan Kim
2016-10-11  4:19           ` Minchan Kim
2016-10-11  9:40           ` Vlastimil Babka
2016-10-11  9:40             ` Vlastimil Babka
2016-10-12  5:36           ` Mel Gorman
2016-10-12  5:36             ` Mel Gorman
2016-10-07  5:45 ` [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic Minchan Kim
2016-10-07  5:45   ` Minchan Kim
2016-10-07 12:44   ` Vlastimil Babka
2016-10-07 12:44     ` Vlastimil Babka
2016-10-07 14:30     ` Minchan Kim [this message]
2016-10-07 14:30       ` Minchan Kim
2016-10-12  5:36   ` Mel Gorman
2016-10-12  5:36     ` Mel Gorman
2016-10-07  5:45 ` [PATCH 3/4] mm: unreserve highatomic free pages fully before OOM Minchan Kim
2016-10-07  5:45   ` Minchan Kim
2016-10-07  9:09   ` Michal Hocko
2016-10-07  9:09     ` Michal Hocko
2016-10-07 14:43     ` Minchan Kim
2016-10-07 14:43       ` Minchan Kim
2016-10-10  7:41       ` Michal Hocko
2016-10-10  7:41         ` Michal Hocko
2016-10-11  5:01         ` Minchan Kim
2016-10-11  5:01           ` Minchan Kim
2016-10-11  6:50           ` Michal Hocko
2016-10-11  6:50             ` Michal Hocko
2016-10-11  7:09             ` Minchan Kim
2016-10-11  7:09               ` Minchan Kim
2016-10-11  7:26               ` Michal Hocko
2016-10-11  7:26                 ` Michal Hocko
2016-10-11  7:37                 ` Minchan Kim
2016-10-11  7:37                   ` Minchan Kim
2016-10-11  8:01                   ` Michal Hocko
2016-10-11  8:01                     ` Michal Hocko
2016-10-07  5:45 ` [PATCH 4/4] mm: skip to reserve pageblock crossed zone boundary for HIGHATOMIC Minchan Kim
2016-10-07  5:45   ` Minchan Kim
2016-10-07  9:16 ` [PATCH 0/4] use up highorder free pages before OOM Michal Hocko
2016-10-07  9:16   ` Michal Hocko
2016-10-07 15:04   ` Minchan Kim
2016-10-07 15:04     ` Minchan Kim
2016-10-10  7:47     ` Michal Hocko
2016-10-10  7:47       ` Michal Hocko
2016-10-11  5:06       ` Minchan Kim
2016-10-11  5:06         ` Minchan Kim
2016-10-11  6:53         ` Michal Hocko
2016-10-11  6:53           ` Michal Hocko

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