From: Vlastimil Babka <vbabka@suse.cz>
To: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
hughd@google.com, mgorman@techsingularity.net,
minchan@kernel.org, stable@vger.kernel.org
Subject: Re: [patch for-4.7] mm, compaction: prevent VM_BUG_ON when terminating freeing scanner
Date: Tue, 5 Jul 2016 23:37:34 +0200 [thread overview]
Message-ID: <577C289E.9020403@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1607051357050.110721@chino.kir.corp.google.com>
On 07/05/2016 11:01 PM, David Rientjes wrote:
> On Thu, 30 Jun 2016, Vlastimil Babka wrote:
>
>>> Note: I really dislike the low watermark check in split_free_page() and
>>> consider it poor software engineering. The function should split a free
>>> page, nothing more. Terminating memory compaction because of a low
>>> watermark check when we're simply trying to migrate memory seems like an
>>> arbitrary heuristic. There was an objection to removing it in the first
>>> proposed patch, but I think we should really consider removing that
>>> check so this is simpler.
>>
>> There's a patch changing it to min watermark (you were CC'd on the series). We
>> could argue whether it belongs to split_free_page() or some wrapper of it, but
>> I don't think removing it completely should be done. If zone is struggling
>> with order-0 pages, a functionality for making higher-order pages shouldn't
>> make it even worse. It's also not that arbitrary, even if we succeeded the
>> migration and created a high-order page, the higher-order allocation would
>> still fail due to watermark checks. Worse, __compact_finished() would keep
>> telling the compaction to continue, creating an even longer lag, which is also
>> against your recent patches.
>>
>
> I'm suggesting we shouldn't check any zone watermark in split_free_page():
> that function should just split the free page.
>
> I don't find our current watermark checks to determine if compaction is
> worthwhile to be invalid, but I do think that we should avoid checking or
> acting on any watermark in isolate_freepages() itself. We could do more
> effective checking in __compact_finished() to determine if we should
> terminate compaction, but the freeing scanner feels like the wrong place
> to do it -- it's also expensive to check while gathering free pages for
> memory that we have already successfully isolated as part of the
> iteration.
>
> Do you have any objection to this fix for 4.7?
No.
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Joonson and/or Minchan, does this address the issue that you reported?
>
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WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
hughd@google.com, mgorman@techsingularity.net,
minchan@kernel.org, stable@vger.kernel.org
Subject: Re: [patch for-4.7] mm, compaction: prevent VM_BUG_ON when terminating freeing scanner
Date: Tue, 5 Jul 2016 23:37:34 +0200 [thread overview]
Message-ID: <577C289E.9020403@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1607051357050.110721@chino.kir.corp.google.com>
On 07/05/2016 11:01 PM, David Rientjes wrote:
> On Thu, 30 Jun 2016, Vlastimil Babka wrote:
>
>>> Note: I really dislike the low watermark check in split_free_page() and
>>> consider it poor software engineering. The function should split a free
>>> page, nothing more. Terminating memory compaction because of a low
>>> watermark check when we're simply trying to migrate memory seems like an
>>> arbitrary heuristic. There was an objection to removing it in the first
>>> proposed patch, but I think we should really consider removing that
>>> check so this is simpler.
>>
>> There's a patch changing it to min watermark (you were CC'd on the series). We
>> could argue whether it belongs to split_free_page() or some wrapper of it, but
>> I don't think removing it completely should be done. If zone is struggling
>> with order-0 pages, a functionality for making higher-order pages shouldn't
>> make it even worse. It's also not that arbitrary, even if we succeeded the
>> migration and created a high-order page, the higher-order allocation would
>> still fail due to watermark checks. Worse, __compact_finished() would keep
>> telling the compaction to continue, creating an even longer lag, which is also
>> against your recent patches.
>>
>
> I'm suggesting we shouldn't check any zone watermark in split_free_page():
> that function should just split the free page.
>
> I don't find our current watermark checks to determine if compaction is
> worthwhile to be invalid, but I do think that we should avoid checking or
> acting on any watermark in isolate_freepages() itself. We could do more
> effective checking in __compact_finished() to determine if we should
> terminate compaction, but the freeing scanner feels like the wrong place
> to do it -- it's also expensive to check while gathering free pages for
> memory that we have already successfully isolated as part of the
> iteration.
>
> Do you have any objection to this fix for 4.7?
No.
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Joonson and/or Minchan, does this address the issue that you reported?
>
next prev parent reply other threads:[~2016-07-05 21:37 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-29 21:47 [patch for-4.7] mm, compaction: prevent VM_BUG_ON when terminating freeing scanner David Rientjes
2016-06-29 21:47 ` David Rientjes
2016-06-29 22:37 ` Greg KH
2016-06-29 22:37 ` Greg KH
2016-06-30 7:17 ` Vlastimil Babka
2016-06-30 7:17 ` Vlastimil Babka
2016-07-05 21:01 ` David Rientjes
2016-07-05 21:01 ` David Rientjes
2016-07-05 21:37 ` Vlastimil Babka [this message]
2016-07-05 21:37 ` Vlastimil Babka
2016-07-06 1:41 ` Joonsoo Kim
2016-07-06 1:41 ` Joonsoo Kim
2016-07-06 1:55 ` Minchan Kim
2016-07-06 1:55 ` Minchan Kim
2016-07-06 1:55 ` Minchan Kim
2016-07-06 1:39 ` Joonsoo Kim
2016-07-06 1:39 ` Joonsoo Kim
2016-07-06 6:50 ` Minchan Kim
2016-07-06 6:50 ` Minchan Kim
2016-07-06 6:50 ` Minchan Kim
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