linux-kernel - Re: [PATCH 0/4] cpuset: cleanups and fixes

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Message-Id: <20090226163954.db4af9fc.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 26 Feb 2009 16:39:54 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] cpuset: cleanups and fixes

On Thu, 26 Feb 2009 15:02:15 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> This patchset mainly simplifies update_tasks_nodemask() and makes it
> return void (won't fail), thus fix a case that writing to cpuset.mems
> returns -ENOMEM but its mems_allowed has been changed.
> 
> [PATCH 1/4] cgroups: add 'data' field to struct cgroup_scanner
> [PATCH 2/4] cpuset: rewrite update_tasks_nodemask()
> [PATCH 3/4] cpuset: avoid changing cpuset's mems when errno returned
> [PATCH 4/4] cpuset: remove struct cpuset_hotplug_scanner
> 
Thank you. I think there is no problematic in your patch.

After reading your patch, I wonder we can improve this migration by
filter for cgroup_scan_tasks().

Assume a task with tons of threads in a cgroup and
  - change nodemask
  - migrate=1

Under current implemntation, cpuset_migrate_mm=>do_migrate_mm is called per
threads. This implies there will be big overhead, useless scanning of page
tables.

Can we add some checks as "Is this mm already migrated ?", anywhere ?
(we may need to add some another array, again...)

Thanks,
-Kame







> ---
>  include/linux/cgroup.h |    1
>  kernel/cpuset.c        |  151 +++++++++++++++++++------------------------------
>  2 files changed, 62 insertions(+), 90 deletions(-)
> ---
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
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