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[195.135.220.15]) by mx.google.com with ESMTPS id 32si3199230eds.25.2019.05.21.03.37.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 May 2019 03:37:27 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 452F8AF1C; Tue, 21 May 2019 10:37:27 +0000 (UTC) Date: Tue, 21 May 2019 12:37:26 +0200 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , linux-api@vger.kernel.org Subject: Re: [RFC 6/7] mm: extend process_madvise syscall to support vector arrary Message-ID: <20190521103726.GM32329@dhcp22.suse.cz> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-7-minchan@kernel.org> <20190520092258.GZ6836@dhcp22.suse.cz> <20190521024820.GG10039@google.com> <20190521062421.GD32329@dhcp22.suse.cz> <20190521102613.GC219653@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521102613.GC219653@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Tue 21-05-19 19:26:13, Minchan Kim wrote: > On Tue, May 21, 2019 at 08:24:21AM +0200, Michal Hocko wrote: > > On Tue 21-05-19 11:48:20, Minchan Kim wrote: > > > On Mon, May 20, 2019 at 11:22:58AM +0200, Michal Hocko wrote: > > > > [Cc linux-api] > > > > > > > > On Mon 20-05-19 12:52:53, Minchan Kim wrote: > > > > > Currently, process_madvise syscall works for only one address range > > > > > so user should call the syscall several times to give hints to > > > > > multiple address range. > > > > > > > > Is that a problem? How big of a problem? Any numbers? > > > > > > We easily have 2000+ vma so it's not trivial overhead. I will come up > > > with number in the description at respin. > > > > Does this really have to be a fast operation? I would expect the monitor > > is by no means a fast path. The system call overhead is not what it used > > to be, sigh, but still for something that is not a hot path it should be > > tolerable, especially when the whole operation is quite expensive on its > > own (wrt. the syscall entry/exit). > > What's different with process_vm_[readv|writev] and vmsplice? > If the range needed to be covered is a lot, vector operation makes senese > to me. I am not saying that the vector API is wrong. All I am trying to say is that the benefit is not really clear so far. If you want to push it through then you should better get some supporting data. -- Michal Hocko SUSE Labs