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From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	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: Wed, 5 Dec 2018 08:06:47 +0000	[thread overview]
Message-ID: <20181205080647.GW23260@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. 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...
> 

Andrew, would you mind dropping this patch from mmotm please? I think
the benefit is marginal relative to the potential loss. If it turns out
we ever really do need it then hopefully there will be better data
supporting it.

Thanks.

-- 
Mel Gorman
SUSE Labs

      parent reply	other threads:[~2018-12-05  8:06 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
2018-12-05  8:06     ` Mel Gorman [this message]

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