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Date: Sat, 12 May 2012 08:40:39 +0530
Message-ID: <CAMYGaxrYex7ALY4_5R_jTz-xftu6zVD3-SmUdVDO-Gy4Vom7gA@mail.gmail.com>
Subject: Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per
 user_struct spinlock
From: rajman mekaco <rajman.mekaco@gmail.com>
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To: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Paul Gortmaker <paul.gortmaker@windriver.com>, Andrew Morton <akpm@linux-foundation.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Minchan Kim <minchan.kim@gmail.com>, Christoph Lameter <cl@gentwo.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

>>
>> 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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