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From: Vlastimil Babka <vbabka@suse.cz>
To: Minchan Kim <minchan@kernel.org>
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 1/4] mm: adjust reserved highatomic count
Date: Mon, 10 Oct 2016 08:57:40 +0200	[thread overview]
Message-ID: <c0920ac2-fe63-567e-e24c-eb6d638143b0@suse.cz> (raw)
In-Reply-To: <20161007142919.GA3060@bbox>

On 10/07/2016 04:29 PM, Minchan Kim wrote:
>>> In that case, we should adjust nr_reserved_highatomic.
>>> Otherwise, VM cannot reserve highorderatomic pageblocks any more
>>> although it doesn't reach 1% limit. It means highorder atomic
>>> allocation failure would be higher.
>>>
>>> So, this patch decreases the account as well as migratetype
>>> if it was MIGRATE_HIGHATOMIC.
>>>
>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>
>> Hm wouldn't it be simpler just to prevent the pageblock's migratetype to be
>> changed if it's highatomic? Possibly also not do move_freepages_block() in
>
> It could be. Actually, I did it with modifying can_steal_fallback which returns
> false it found the pageblock is highorderatomic but changed to this way again
> because I don't have any justification to prevent changing pageblock.
> If you give concrete justification so others isn't against on it, I am happy to
> do what you suggested.

Well, MIGRATE_HIGHATOMIC is not listed in the fallbacks array at all, so 
we are not supposed to steal from it in the first place. Stealing will 
only happen due to races, which would be too costly to close, so we 
allow them and expect to be rare. But we shouldn't allow them to break 
the accounting.

WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Minchan Kim <minchan@kernel.org>
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 1/4] mm: adjust reserved highatomic count
Date: Mon, 10 Oct 2016 08:57:40 +0200	[thread overview]
Message-ID: <c0920ac2-fe63-567e-e24c-eb6d638143b0@suse.cz> (raw)
In-Reply-To: <20161007142919.GA3060@bbox>

On 10/07/2016 04:29 PM, Minchan Kim wrote:
>>> In that case, we should adjust nr_reserved_highatomic.
>>> Otherwise, VM cannot reserve highorderatomic pageblocks any more
>>> although it doesn't reach 1% limit. It means highorder atomic
>>> allocation failure would be higher.
>>>
>>> So, this patch decreases the account as well as migratetype
>>> if it was MIGRATE_HIGHATOMIC.
>>>
>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>
>> Hm wouldn't it be simpler just to prevent the pageblock's migratetype to be
>> changed if it's highatomic? Possibly also not do move_freepages_block() in
>
> It could be. Actually, I did it with modifying can_steal_fallback which returns
> false it found the pageblock is highorderatomic but changed to this way again
> because I don't have any justification to prevent changing pageblock.
> If you give concrete justification so others isn't against on it, I am happy to
> do what you suggested.

Well, MIGRATE_HIGHATOMIC is not listed in the fallbacks array at all, so 
we are not supposed to steal from it in the first place. Stealing will 
only happen due to races, which would be too costly to close, so we 
allow them and expect to be rare. But we shouldn't allow them to break 
the accounting.


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  reply	other threads:[~2016-10-10  7:33 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 [this message]
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
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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