Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock

Rik van Riel
2012-05-10T22:30:59Z

On 05/10/2012 11:39 AM, rajman mekaco wrote:
> On Thu, May 10, 2012 at 8:24 PM, Rik van Riel<riel@redhat.com> wrote:
>> On 05/10/2012 09:34 AM, rajman mekaco wrote:
>>
>>> Any updates on this ?
>>
>>
>> There is still no usecase to demonstrate a problem, so no real
>> justification to merge the patch. Coming up with such a usecase
>> is up to the submitter of the patch.
>
> 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?

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