linux-kernel - Re: [PATCH] mm: limit direct reclaim for higher order allocations

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Date:	Wed, 24 Feb 2016 21:47:27 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	David Rientjes <rientjes@...gle.com>, linux-kernel@...r.kernel.org,
	hannes@...xchg.org, akpm@...ux-foundation.org, vbabka@...e.cz,
	mgorman@...e.de
Subject: Re: [PATCH] mm: limit direct reclaim for higher order allocations

On Thu, 2016-02-25 at 09:30 +0900, Joonsoo Kim wrote:
> On Wed, Feb 24, 2016 at 05:17:56PM -0500, Rik van Riel wrote:
> > On Wed, 2016-02-24 at 14:15 -0800, David Rientjes wrote:
> > > On Wed, 24 Feb 2016, Rik van Riel wrote:
> > > 
> > > > For multi page allocations smaller than
> > > > PAGE_ALLOC_COSTLY_ORDER,
> > > > the kernel will do direct reclaim if compaction failed for any
> > > > reason. This worked fine when Linux systems had 128MB RAM, but
> > > > on my 24GB system I frequently see higher order allocations
> > > > free up over 3GB of memory, pushing all kinds of things into
> > > > swap, and slowing down applications.
> > > >  
> > > 
> > > Just curious, are these higher order allocations typically done
> > > by
> > > the 
> > > slub allocator or where are they coming from?
> > 
> > These are slab allocator ones, indeed.
> > 
> > The allocations seem to be order 2 and 3, mostly
> > on behalf of the inode cache and alloc_skb.
> 
> Hello, Rik.
> 
> Could you tell me the kernel version you tested?
> 
> Commit 45eb00cd3a03 (mm/slub: don't wait for high-order page
> allocation) changes slub allocator's behaviour that high order
> allocation request by slub doesn't cause direct reclaim.

The system I observed the problem on has a
4.2 based kernel on it. That would explain.

Are we sure the problem is limited just to
slub, though?

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