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

From: Rik van Riel
Date: Thu May 10 2012 - 18:30:55 EST

On 05/10/2012 11:39 AM, rajman mekaco wrote:
On Thu, May 10, 2012 at 8:24 PM, Rik van Riel<riel@xxxxxxxxxx> 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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