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Date:   Wed, 12 Oct 2022 19:22:21 +0800
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Subject: Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy()
To:     Michal Hocko <mhocko@suse.com>
Cc:     corbet@lwn.net, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
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From:   Zhongkun He <hezhongkun.hzk@bytedance.com>
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> 
> Yes, this will require some refactoring and one potential way is to make
> mpol ref counting unconditional. The conditional ref. counting has
> already caused issues in the past and the code is rather hard to follow
> anyway. I am not really sure this optimization is worth it.
> 
> Another option would be to block the pidfd side of things on completion
> which would wake it up from the task_work context but I would rather
> explore the ref counting approach first and only if this is proven to be
> too expensive to go with hacks like this.

Hi Michal

The counting approach means executing mpol_get/put() when start/finish 
using mempolicy,right?  With the addition of lock add/dec on the hot 
path, the performance may be degraded.

I'll try it to see its performance impact in detail.


Thanks.