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From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>,
	Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@quantum.com>,
	Olaf Hering <olaf@aepfle.de>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 0/4] reintroduce compaction feedback for OOM decisions
Date: Fri, 23 Sep 2016 12:55:23 +0200	[thread overview]
Message-ID: <9194950c-06b5-31d7-de17-1f8710dd5682@suse.cz> (raw)
In-Reply-To: <20160923082627.GE4478@dhcp22.suse.cz>

On 09/23/2016 10:26 AM, Michal Hocko wrote:
>>  include/linux/compaction.h |  5 +++--
>>  mm/compaction.c            | 44 +++++++++++++++++++++++---------------------
>>  mm/internal.h              |  1 +
>>  mm/vmscan.c                |  6 ++++--
>>  4 files changed, 31 insertions(+), 25 deletions(-)
> 
> This is much more code churn than I expected. I was thiking about it
> some more and I am really wondering whether it actually make any sense
> to check the fragidx for !costly orders. Wouldn't it be much simpler to
> just put it out of the way for those regardless of the compaction
> priority. In other words does this check makes any measurable difference
> for !costly orders?

I've did some stress tests and sampling
/sys/kernel/debug/extfrag/extfrag_index once per second. The lowest
value I've got for order-2 was 0.705. The default threshold is 0.5, so
this would still result in compaction considered as suitable.

But it's sampling so I might not got to the interesting moments, most of
the time it was -1.000 which means the page should be just available.
Also we would be changing behavior for the user-controlled
vm.extfrag_threshold, so I'm not entirely sure about that.

I could probably reduce the churn so that compaction_suitable() doesn't
need a new parameter. We could just skip compaction_suitable() check
from compact_zone() on the highest priority, and go on even without
sufficient free page gap?

WARNING: multiple messages have this Message-ID
From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>,
	Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@quantum.com>,
	Olaf Hering <olaf@aepfle.de>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 0/4] reintroduce compaction feedback for OOM decisions
Date: Fri, 23 Sep 2016 12:55:23 +0200	[thread overview]
Message-ID: <9194950c-06b5-31d7-de17-1f8710dd5682@suse.cz> (raw)
In-Reply-To: <20160923082627.GE4478@dhcp22.suse.cz>

On 09/23/2016 10:26 AM, Michal Hocko wrote:
>>  include/linux/compaction.h |  5 +++--
>>  mm/compaction.c            | 44 +++++++++++++++++++++++---------------------
>>  mm/internal.h              |  1 +
>>  mm/vmscan.c                |  6 ++++--
>>  4 files changed, 31 insertions(+), 25 deletions(-)
> 
> This is much more code churn than I expected. I was thiking about it
> some more and I am really wondering whether it actually make any sense
> to check the fragidx for !costly orders. Wouldn't it be much simpler to
> just put it out of the way for those regardless of the compaction
> priority. In other words does this check makes any measurable difference
> for !costly orders?

I've did some stress tests and sampling
/sys/kernel/debug/extfrag/extfrag_index once per second. The lowest
value I've got for order-2 was 0.705. The default threshold is 0.5, so
this would still result in compaction considered as suitable.

But it's sampling so I might not got to the interesting moments, most of
the time it was -1.000 which means the page should be just available.
Also we would be changing behavior for the user-controlled
vm.extfrag_threshold, so I'm not entirely sure about that.

I could probably reduce the churn so that compaction_suitable() doesn't
need a new parameter. We could just skip compaction_suitable() check
from compact_zone() on the highest priority, and go on even without
sufficient free page gap?

--
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  reply	other threads:[~2016-09-23 10:55 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-06 13:52 Vlastimil Babka
2016-09-06 13:52 ` Vlastimil Babka
2016-09-06 13:52 ` [PATCH 1/4] Revert "mm, oom: prevent premature OOM killer invocation for high order request" Vlastimil Babka
2016-09-06 13:52   ` Vlastimil Babka
2016-09-21 17:04   ` Michal Hocko
2016-09-21 17:04     ` Michal Hocko
2016-09-06 13:52 ` [PATCH 2/4] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka
2016-09-06 13:52   ` Vlastimil Babka
2016-09-21 17:13   ` Michal Hocko
2016-09-21 17:13     ` Michal Hocko
2016-09-22 12:51     ` Vlastimil Babka
2016-09-22 12:51       ` Vlastimil Babka
2016-09-22 14:08       ` Michal Hocko
2016-09-22 14:08         ` Michal Hocko
2016-09-22 14:52         ` Michal Hocko
2016-09-22 14:52           ` Michal Hocko
2016-09-22 14:59           ` Vlastimil Babka
2016-09-22 14:59             ` Vlastimil Babka
2016-09-22 15:06           ` Vlastimil Babka
2016-09-22 15:06             ` Vlastimil Babka
2016-09-23  4:04             ` Hillf Danton
2016-09-23  4:04               ` Hillf Danton
2016-09-23  6:55               ` Vlastimil Babka
2016-09-23  6:55                 ` Vlastimil Babka
2016-09-23  8:23                 ` Michal Hocko
2016-09-23  8:23                   ` Michal Hocko
2016-09-23 10:47                   ` Vlastimil Babka
2016-09-23 10:47                     ` Vlastimil Babka
2016-09-23 12:06                     ` Michal Hocko
2016-09-23 12:06                       ` Michal Hocko
2016-09-06 13:52 ` [PATCH 3/4] mm, compaction: restrict full priority to non-costly orders Vlastimil Babka
2016-09-06 13:52   ` Vlastimil Babka
2016-09-21 17:15   ` Michal Hocko
2016-09-21 17:15     ` Michal Hocko
2016-09-06 13:52 ` [PATCH 4/4] mm, compaction: make full priority ignore pageblock suitability Vlastimil Babka
2016-09-06 13:52   ` Vlastimil Babka
2016-09-15 18:51 ` [PATCH 0/4] reintroduce compaction feedback for OOM decisions Arkadiusz Miskiewicz
2016-09-15 18:51   ` Arkadiusz Miskiewicz
2016-09-21 17:18 ` Michal Hocko
2016-09-21 17:18   ` Michal Hocko
2016-09-22 15:18   ` Vlastimil Babka
2016-09-22 15:18     ` Vlastimil Babka
2016-09-23  8:26     ` Michal Hocko
2016-09-23  8:26       ` Michal Hocko
2016-09-23 10:55       ` Vlastimil Babka [this message]
2016-09-23 10:55         ` Vlastimil Babka
2016-09-23 12:09         ` Michal Hocko
2016-09-23 12:09           ` Michal Hocko

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