All of lore.kernel.org
 help / color / mirror / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
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 14:09:59 +0200	[thread overview]
Message-ID: <20160923120958.GM4478@dhcp22.suse.cz> (raw)
In-Reply-To: <9194950c-06b5-31d7-de17-1f8710dd5682@suse.cz>

On Fri 23-09-16 12:55:23, Vlastimil Babka wrote:
> 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.

Does anybody depend on that or even use it out there? I strongly suspect
this is one of those dark corners people even do not know they exist...

> 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?

Whatever makes the code easier to understand. Please do not take me
wrong I do not want to push back on this too hard I just always love to
get rid of an obscure heuristic which even might not matter. And as your
testing suggests this might really be the case for !costly orders AFAIU.
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID
From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
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 14:09:59 +0200	[thread overview]
Message-ID: <20160923120958.GM4478@dhcp22.suse.cz> (raw)
In-Reply-To: <9194950c-06b5-31d7-de17-1f8710dd5682@suse.cz>

On Fri 23-09-16 12:55:23, Vlastimil Babka wrote:
> 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.

Does anybody depend on that or even use it out there? I strongly suspect
this is one of those dark corners people even do not know they exist...

> 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?

Whatever makes the code easier to understand. Please do not take me
wrong I do not want to push back on this too hard I just always love to
get rid of an obscure heuristic which even might not matter. And as your
testing suggests this might really be the case for !costly orders AFAIU.
-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2016-09-23 12:10 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
2016-09-23 10:55         ` Vlastimil Babka
2016-09-23 12:09         ` Michal Hocko [this message]
2016-09-23 12:09           ` Michal Hocko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20160923120958.GM4478@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=Ralf-Peter.Rohbeck@quantum.com \
    --cc=a.miskiewicz@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=olaf@aepfle.de \
    --cc=riel@redhat.com \
    --cc=rientjes@google.com \
    --cc=torvalds@linux-foundation.org \
    --cc=vbabka@suse.cz \
    --subject='Re: [PATCH 0/4] reintroduce compaction feedback for OOM decisions' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.