linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Zi Yan <zi.yan@cs.rutgers.edu>, Michal Hocko <mhocko@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 5/5] mm: Stall movable allocations until kswapd progresses during serious external fragmentation event
Date: Tue, 27 Nov 2018 17:51:11 +0000	[thread overview]
Message-ID: <20181127175111.GT23260@techsingularity.net> (raw)
In-Reply-To: <e0867205-e5f1-b007-5dc7-bb4655f6e5c1@suse.cz>

On Tue, Nov 27, 2018 at 02:20:30PM +0100, Vlastimil Babka wrote:
> > This patch has a marginal rate on fragmentation rates as it's rare for
> > the stall logic to actually trigger but the small stalls can be enough for
> > kswapd to catch up. How much that helps is variable but probably worthwhile
> > for long-term allocation success rates. It is possible to eliminate
> > fragmentation events entirely with tuning due to this patch although that
> > would require careful evaluation to determine if it's worthwhile.
> > 
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> 
> The gains here are relatively smaller and noisier than for the previous
> patches.

Indeed, in an earlier illogical version then it had a bigger impact but
that was due to buggy side-effects.

> Also I'm afraid that once antifrag loses against the ultimate
> adversary workload (see the "Caching/buffers become useless after some
> time" thread), then this might result in adding stalls to a workload
> that has no other options but to allocate movable pages from partially
> filled unmovable blocks, because that's simply the majority of
> pageblocks in the system, and the stalls can't help the situation. If
> that proves to be true, we could revert, but then there's the new
> user-visible tunable... and that all makes it harder for me to decide
> about this patch :) If only we could find out early while this is in
> linux-mm/linux-next...
> 

I think in the event it has to revert that it would be ok for the tuning
to disappear at the same time. There are occasions where a particular
tuning has side-effects that make it harder to remove the interface but
in this case, the tuning is directly related to the patch itself.

That said, stalling behaviour has been problematic so if we want to play
it safe then I do not mind this patch being dropped until there is a
definite benefit from it as the bulk of the series benefit is from the
first 4 patches.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2018-11-27 17:51 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-23 11:45 [PATCH 0/5] Fragmentation avoidance improvements v5 Mel Gorman
2018-11-23 11:45 ` [PATCH 1/5] mm, page_alloc: Spread allocations across zones before introducing fragmentation Mel Gorman
2018-11-26 12:36   ` Vlastimil Babka
2018-11-23 11:45 ` [PATCH 2/5] mm: Move zone watermark accesses behind an accessor Mel Gorman
2018-11-23 11:45 ` [PATCH 3/5] mm: Use alloc_flags to record if kswapd can wake Mel Gorman
2018-11-26 13:38   ` Vlastimil Babka
2018-11-26 14:35     ` [PATCH] mm: Use alloc_flags to record if kswapd can wake -fix Mel Gorman
2018-11-23 11:45 ` [PATCH 4/5] mm: Reclaim small amounts of memory when an external fragmentation event occurs Mel Gorman
2018-11-27  9:23   ` Vlastimil Babka
2018-11-23 11:45 ` [PATCH 5/5] mm: Stall movable allocations until kswapd progresses during serious external fragmentation event Mel Gorman
2018-11-27 13:20   ` Vlastimil Babka
2018-11-27 17:51     ` Mel Gorman [this message]
2018-12-05  8:06     ` Mel Gorman

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=20181127175111.GT23260@techsingularity.net \
    --to=mgorman@techsingularity.net \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@kernel.org \
    --cc=rientjes@google.com \
    --cc=vbabka@suse.cz \
    --cc=zi.yan@cs.rutgers.edu \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).