linux-kernel - Re: [PATCH 1/2] break out page allocation warning code

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Message-ID: <alpine.DEB.2.00.1104281545590.24536@chino.kir.corp.google.com>
Date:	Thu, 28 Apr 2011 15:48:25 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	john stultz <johnstul@...ibm.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] break out page allocation warning code

On Wed, 27 Apr 2011, john stultz wrote:

> So thinking further, this can be simplified by adding the seqlock first,
> and then retaining the task_locking only in the set_task_comm path until
> all comm accessors are converted to using get_task_comm.
> 

On second thought, I think it would be better to just retain using a 
spinlock but instead of using alloc_lock, introduce a new spinlock to 
task_struct for the sole purpose of protecting comm.

And, instead, of using get_task_comm() to write into a preallocated 
buffer, I think it would be easier in the vast majority of cases that 
you'll need to convert to just provide task_comm_lock(p) and 
task_comm_unlock(p) so that p->comm can be dereferenced safely.  
get_task_comm() could use that interface itself and then write into a 
preallocated buffer.

The problem with using get_task_comm() everywhere is it requires 16 
additional bytes to be allocated on the stack in hundreds of locations 
around the kernel which may or may not be safe.
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