linux-kernel - Re: [PATCH] mm,vmscan: compact memory from kswapd when lots of memory free already

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Message-ID: <1456241996.7716.34.camel@surriel.com>
Date:	Tue, 23 Feb 2016 10:39:56 -0500
From:	Rik van Riel <riel@...riel.com>
To:	Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org
Cc:	linux-mm@...ck.org, hannes@...xchg.org, akpm@...ux-foundation.org,
	mgorman@...e.de
Subject: Re: [PATCH] mm,vmscan: compact memory from kswapd when lots of
 memory free already

On Tue, 2016-02-23 at 10:18 +0100, Vlastimil Babka wrote:
> On 02/23/2016 04:50 AM, Rik van Riel wrote:
> > If kswapd is woken up for a higher order allocation, for example
> > from alloc_skb, but the system already has lots of memory free,
> > kswapd_shrink_zone will rightfully decide kswapd should not free
> > any more memory.
> > 
> > However, at that point kswapd should proceed to compact memory, on
> > behalf of alloc_skb or others.
> > 
> > Currently kswapd will only compact memory if it first freed memory,
> > leading kswapd to never compact memory when there is already lots
> > of
> > memory free.
> > 
> > On my home system, that lead to kswapd occasionally using up to 5%
> > CPU time, with many man wakeups from alloc_skb, and kswapd never
> > doing anything to relieve the situation that caused it to be woken
> > up.
> 
> Hi,
> 
> I've proposed replacing kswapd compaction with kcompactd, so this
> hunk 
> is gone completely in mmotm. This imperfect comparison was indeed one
> of 
> the things I've noted, but it's not all:
> 
> http://marc.info/?l=linux-kernel&m=145493881908394&w=2

Never mind my patch, then. Your solution is nicer,
and already in -mm :)

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