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Date: Fri, 19 Feb 2010 21:13:16 +0530
Message-ID: <661de9471002190743t5385d97hf38c544f0007879c@mail.gmail.com>
Subject: Re: [PATCH] powerpc: Set a smaller value for RECLAIM_DISTANCE to
	enable zone reclaim
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Anton Blanchard <anton@samba.org>
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On Fri, Feb 19, 2010 at 3:59 AM, Anton Blanchard <anton@samba.org> wrote:
>
> I noticed /proc/sys/vm/zone_reclaim_mode was 0 on a ppc64 NUMA box. It ge=
ts
> enabled via this:
>
> =A0 =A0 =A0 =A0/*
> =A0 =A0 =A0 =A0 * If another node is sufficiently far away then it is bet=
ter
> =A0 =A0 =A0 =A0 * to reclaim pages in a zone before going off node.
> =A0 =A0 =A0 =A0 */
> =A0 =A0 =A0 =A0if (distance > RECLAIM_DISTANCE)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0zone_reclaim_mode =3D 1;
>
> Since we use the default value of 20 for REMOTE_DISTANCE and 20 for
> RECLAIM_DISTANCE it never kicks in.
>
> The local to remote bandwidth ratios can be quite large on System p
> machines so it makes sense for us to reclaim clean pagecache locally befo=
re
> going off node.
>
> The patch below sets a smaller value for RECLAIM_DISTANCE and thus enable=
s
> zone reclaim.
>

A reclaim distance of 10 implies a ratio of 1, that means we'll always
do zone_reclaim() to free page cache and slab cache before moving on
to another node?

Balbir Singh.