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Thu, 13 Oct 2022 06:42:36 -0700 (PDT) Message-ID: Date: Thu, 13 Oct 2022 21:42:30 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.2 Subject: Re: [External] Re: [RFC] mm: add new syscall pidfd_set_mempolicy() To: Michal Hocko Cc: corbet@lwn.net, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, wuyun.abel@bytedance.com References: <20221010094842.4123037-1-hezhongkun.hzk@bytedance.com> <582cf257-bc0d-c96e-e72e-9164cff4fce1@bytedance.com> From: Zhongkun He In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665668560; a=rsa-sha256; cv=none; b=3aFoqTZu64KYZsaxZ3XjVQo0ZMmwPTs/RHXYPhiJ5Q5uVBNZ0fjurn01jegDD7cXxRq6lE ViJkSUiCSzK5js6Jv3NGcj/88h79jo2tdabFm3KpUE5qOjq0RuXz4k60/xCYjjvsCa9q+r mwL7zGQ+27df3TK+g7vWuWsS4sD60uU= ARC-Authentication-Results: i=1; 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dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b="AvHPQ5/w"; spf=pass (imf06.hostedemail.com: domain of hezhongkun.hzk@bytedance.com designates 209.85.216.43 as permitted sender) smtp.mailfrom=hezhongkun.hzk@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-HE-Tag: 1665668557-842272 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Thu 13-10-22 20:50:48, Zhongkun He wrote: >>>> 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. Got it, thanks for your reply and suggestions.