linux-kernel - Re: [External] Re: [RFC] mm: add new syscall pidfd_set

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Message-ID: <db41c662-19ce-fc1a-21ba-38ecda7d09c8@bytedance.com>
Date:   Thu, 13 Oct 2022 20:50:48 +0800
From:   Zhongkun He <hezhongkun.hzk@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     corbet@....net, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, wuyun.abel@...edance.com
Subject: Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy()

>> 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.

Thanks.