linux-kernel - Re: [PATCH 2/4] posix-timers: limit the number of posix timers per process

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Message-Id: <20110830144407.acdae071.akpm@linux-foundation.org>
Date:	Tue, 30 Aug 2011 14:44:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, eric.dumazet@...il.com,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/4] posix-timers: limit the number of posix timers per
 process

On Mon, 29 Aug 2011 16:39:15 -0700
Andi Kleen <andi@...stfloor.org> wrote:

> Now this is the main reason I wrote the whole patchkit: previously
> there was no limit on the maximum number of POSIX timers a process
> could allocate.  This limits the amount of unswappable kernel memory
> a process can pin down this way.
> 
> With the POSIX timer ids being per process we can do this limit
> per process now without allowing one process DoSing another.
> 
> I implemented it as a sysctl, not a rlimit for now, because
> there was no clear use case for rlimit.
> 
> The 1024 default is completely arbitrary, but seems reasonable
> for now.

Sorry, it should be an rlimit from day one, IMO.

Partly because rlimits are a better implementation.

Partly because if we later do it via rlimit, we're stuck having to
maintain the /proc knob for ever.

Partly because once rlimits are added, the /proc knob no longer has any
sane behaviour.  Does it only modify /sbin/init?  Does it do a global
process walk, modifying all threads?
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