linux-kernel - Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user

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Message-ID: <4FA2EA4A.6040703@redhat.com>
Date:	Thu, 03 May 2012 16:27:54 -0400
From:	Rik van Riel <riel@...hat.com>
To:	rajman mekaco <rajman.mekaco@...il.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...two.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into
 per user_struct spinlock

On 05/03/2012 02:07 PM, Rik van Riel wrote:
> On 05/03/2012 01:34 PM, rajman mekaco wrote:
>> The user_shm_lock and user_shm_unlock functions use a single global
>> spinlock for protecting the user->locked_shm.
>>
>> This is an overhead for multiple CPUs calling this code even if they
>> are having different user_struct.
>>
>> Remove the global shmlock_user_lock and introduce and use a new
>> spinlock inside of the user_struct structure.
>>
>> Signed-off-by: rajman mekaco<rajman.mekaco@...il.com>
>
> Reviewed-by: Rik van Riel <riel@...hat.com>

Hold this ... while the patch is correct, Peter raised
a valid concern about its usefulness, which should be
sorted out first.

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