linux-kernel - Re: A Plumber’s Wish List for Linux

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Message-ID: <4EAF4B16.6030505@cn.fujitsu.com>
Date:	Tue, 01 Nov 2011 09:27:50 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Lennart Poettering <mzxreary@...inter.de>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Menage <paul@...lmenage.org>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, harald@...hat.com, david@...ar.dk,
	greg@...ah.com
Subject: Re: A Plumber’s Wish List for Linux

Lennart Poettering wrote:
> On Tue, 25.10.11 13:40, Li Zefan (lizf@...fujitsu.com) wrote:
> 
>>> cgroups provides us with all of that, though the last two items only in
>>> a suboptimal way: notification of cgroups running empty is ugly, since
>>> it is done by spawning a usermode helper (we'd prefer a netlink msg or
>>> so), and the process killing is a bit racy.
>>
>> How about using eventfd? You can create an eventfd for the specific "tasks"
>> file, and when the cgroup gets empty (no task in it), you'll get a notification.
>>
>> It should be easy to implement, since cgroup already supports eventfd-based
>> API.
> 
> I am quite convinced that using eventfd() like this is quite ugly. The
> current evetnfd() logic is not recursive anyway, hence wouldn't help us
> much.
> 

I remember in an earlier email you stated you want to be able to kill all tasks
in a cgroup and its children, and you used the word "recursive", but what do you
mean by ""recursive" for empty cgroup notification, do you expect the listener
to recieve a message if a cgroup or any of its children becomes empty?
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