linux-kernel - Re: [PATCH] - New round-robin rotor for SLAB allocations

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Message-Id: <20100430135239.7782f6ba.akpm@linux-foundation.org>
Date:	Fri, 30 Apr 2010 13:52:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jack Steiner <steiner@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	cl@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] - New round-robin rotor for SLAB allocations

On Mon, 26 Apr 2010 16:00:41 -0500
Jack Steiner <steiner@....com> wrote:

> We have observed several workloads running on multi-node systems where
> memory is assigned unevenly across the nodes in the system. There are
> numerous reasons for this but one is the round-robin rotor in
> cpuset_mem_spread_node().
> 
> For example, a simple test that writes a multi-page file will allocate pages
> on nodes 0 2 4 6 ... Odd nodes are skipped.  (Sometimes it allocates on
> odd nodes & skips even nodes).
> 
> An example is shown below. The program "lfile" writes a file consisting of
> 10 pages. The program then mmaps the file & uses get_mempolicy(...,
> MPOL_F_NODE) to determine the nodes where the file pages were allocated.
> The output is shown below:
> 
> 	# ./lfile
> 	 allocated on nodes: 2 4 6 0 1 2 6 0 2
> 
> 
> 
> There is a single rotor that is used for allocating both file pages & slab
> pages.  Writing the file allocates both a data page & a slab page
> (buffer_head).  This advances the RR rotor 2 nodes for each page
> allocated.
> 
> A quick confirmation seems to confirm this is the cause of the uneven
> allocation:
> 
> 	# echo 0 >/dev/cpuset/memory_spread_slab
> 	# ./lfile
> 	 allocated on nodes: 6 7 8 9 0 1 2 3 4 5
> 
> 
> This patch introduces a second rotor that is used for slab allocations.
>
>  include/linux/cpuset.h |    6 ++++++
>  include/linux/sched.h  |    1 +
>  kernel/cpuset.c        |   20 ++++++++++++++++----
>  mm/slab.c              |    2 +-
>  4 files changed, 24 insertions(+), 5 deletions(-)

Why no update to slob and slub?
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