linux-kernel - Re: [patch] mm, hugetlb: add thread name and pid to SHM

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Date:	Thu, 8 Mar 2012 14:23:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Dave Jones <davej@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] mm, hugetlb: add thread name and pid to SHM_HUGETLB
 mlock rlimit warning

On Thu, 8 Mar 2012 14:08:30 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Thu, 8 Mar 2012, Andrew Morton wrote:
> 
> > >  We have a get_task_comm() that does the task_lock() 
> > > internally but requires a TASK_COMM_LEN buffer in the calling code.  It's 
> > > just easier for the calling code to the task_lock() itself for a tiny 
> > > little printk().
> > 
> > Well for a tiny little printk we could just omit the locking?  The
> > printk() won't oops and once in a million years one person will see a
> > garbled comm[] string?
> > 
> 
> Sure, but task_lock() shouldn't be highly contended when the thread isn't 
> forking or exiting (everything else is attaching/detaching from a cgroup 
> or testing a mempolicy).  I've always added it (like in the oom killer for 
> the same reason) just because the race exists.  Taking it for every thread 
> on the system for one call to the oom killer has never slowed it down.

I wasn't concerned about the performance side of things - just that
it's such a pain over such a silly thing.

btw, if the code had done

	printk_once(..., get_task_comm(...), ...)

the task_lock() would have been performed just a single time, rather
than every time.


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