lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 13 May 2014 12:46:19 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	lizefan@...wei.com, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, hannes@...xchg.org
Subject: Re: [PATCH 02/14] cgroup: remove pointless has tasks/children test
 from mem_cgroup_force_empty()

On Mon, May 12, 2014 at 04:53:24PM +0200, Michal Hocko wrote:
> From 03f8cb2e1fd2636d859c54df9b58719fe96e0e54 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.cz>
> Date: Mon, 12 May 2014 16:34:17 +0200
> Subject: [PATCH] memcg: remove tasks/children test from from
>  mem_cgroup_force_empty
> 
> Tejun has correctly pointed out that tasks/children test in
> mem_cgroup_force_empty is not correct because there is no other locking
> which preserves this state throughout the rest of the function so both
> new tasks can join the group or new children groups can be added while
> somebody is writing to memory.force_empty. A new task would break
> mem_cgroup_reparent_charges expectation that all failures as described
> by mem_cgroup_force_empty_list are temporal and there is no way out.
> 
> The main use case for the knob as described by
> Documentation/cgroups/memory.txt is to:
> "
>   The typical use case for this interface is before calling rmdir().
>   Because rmdir() moves all pages to parent, some out-of-use page caches can be
>   moved to the parent. If you want to avoid that, force_empty will be useful.
> "
> 
> This means that reparenting is not really required as rmdir will
> reparent pages implicitly from the safe context. If we remove it from
> mem_cgroup_force_empty then we are safe even with existing tasks because
> the number of reclaim attempts is bounded. Moreover the knob still does
> what the documentation claims (modulo reparenting which doesn't make any
> difference) and users might expect. Longterm we want to deprecate the
> whole knob and put the reparented pages to the tail of parent LRU during
> cgroup removal.

Replaced the original patch with this one with Johannes' ack added.

Thanks!

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists