linux-kernel - Re: [patch] cpusets: do not allow TIF

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Date:	Tue, 5 Jun 2007 16:55:38 -0700
From:	Paul Jackson <pj@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	clameter@....com, akpm@...ux-foundation.org, ak@...e.de,
	clameter@...ulhu.engr.sgi.com, linux-kernel@...r.kernel.org
Subject: Re: [patch] cpusets: do not allow TIF_MEMDIE tasks to allocate
 globally

> If that fails, we can't allocate elsewhere because then we have taken 
> exclusive memory from other applications and is contrary to the definition 
> of mem_exclusive. 

Well, I can't speak to the 'real' meaning of TIF_MEMDIE with authority,
but I can speak to the meaning of cpuset flags.

The mem_exclusive flag doesn't mean this.

It means that you cannot overlap the memory of a sibling cpuset.

You will, necessarily, still overlap the memory of your ancestor cpusets.

Whether or not you make any use of the mem_exclusive flag, you still
get the same (limited) guarantees of memory usage -- namely that your
memory won't be used by tasks in non-overlapping cpusets, with some
exceptions, such as:
 1) memory handed out to interrupt code,
 2) memory handed out for GFP_ATOMIC requests, and
 3) tasks marked PF_EXITING -- will soon free up memory

Tasks in cpusets ancestor to your tasks cpuset can always, easily,
use memory on the same nodes your task is on.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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