Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy()

On Thu 13-10-22 20:50:48, Zhongkun He wrote:

quoted

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Hi Michal

Could we try to change the MPOL_F_SHARED flag to MPOL_F_STATIC to
mark static mempolicy which cannot be freed, and mpol_needs_cond_ref
can use MPOL_F_STATIC to avoid freeing  the static mempolicy.

Wouldn't it make more sense to get rid of a different treatment and
treat all memory policies the same way?

I found a case, not sure if it makes sense. If there is no policy
in task->mempolicy, the use of atomic_{inc,dec} can be skiped
according  to MPOL_F_STATIC. Atomic_{inc,dec} in hot path may reduces
performance.

I would start with a simple conversion and do any potential
optimizations on top of that based on actual numbers. Maybe we can
special case default_policy to avoid reference counting a default (no
policy case). A simple check for pol == &default_policy should be
negligible.
-- 
Michal Hocko
SUSE Labs