linux-kernel - Re: [RFC] ps command race fix

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Date:	Mon, 24 Jul 2006 19:33:18 -0700
From:	Andrew Morton <akpm@...l.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	pj@....com, linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: [RFC] ps command race fix

On Tue, 25 Jul 2006 11:08:35 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> > Then the seek and read and such semantics are nice and stable and
> > simple.
> > 
> yes...
> I think snapshot at open() is okay.

We cannot do a single kmalloc() like cpuset does.

The kernel presently kind-of guarantees that a 32k kmalloc() will work,
although the VM might have to do very large amounts of work to achieve it.

But 32k is only 8192 processes, so a snapshot will need multiple
allocations and a list and trouble dropping and retaking tasklist_lock to
allocate memory and keeping things stable while doing that.  I suspect
it'll end up ugly.

And it permits userspace to pin rather a lot of memory.
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