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

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Date:	Sat, 12 May 2012 08:40:39 +0530
From:	rajman mekaco <rajman.mekaco@...il.com>
To:	Rik van Riel <riel@...hat.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

>>
>> Maybe you didn't read my last email:
>> If 2 different user-mode processes executing on 2 CPUs under 2 different
>> users want to access the same shared memory through the
>> shmctl(SHM_LOCK) / shmget(SHM_HUGETLB) / usr_shm_lock
>> primitives, they could compete/spin even though their user_structs
>> are different.
>>
>> Can you please correct me if I am missing some crucial point of
>> understanding ?
>
>
> Mlock is a very very expensive operation.
>
> Updating the mlock statistics is a very cheap operation.
>
> Does this spinlock ever show up contention wise?

I just tested for working and not contention. :)
I was just going by correctness of concept.
But I understand what you say and I will try to actually test contention
for this in the coming days.

>
> --
> All rights reversed
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