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[195.135.220.15]) by mx.google.com with ESMTPS id z36si8139091edb.45.2019.05.21.04.32.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 May 2019 04:32:56 -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 512A5AE14; Tue, 21 May 2019 11:32:55 +0000 (UTC) Date: Tue, 21 May 2019 13:32:54 +0200 From: Michal Hocko To: Minchan Kim Cc: Oleksandr Natalenko , Andrew Morton , LKML , linux-mm , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon Subject: Re: [RFC 4/7] mm: factor out madvise's core functionality Message-ID: <20190521113254.GU32329@dhcp22.suse.cz> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-5-minchan@kernel.org> <20190520142633.x5d27gk454qruc4o@butterfly.localdomain> <20190521012649.GE10039@google.com> <20190521063628.x2npirvs75jxjilx@butterfly.localdomain> <20190521065000.GH32329@dhcp22.suse.cz> <20190521070638.yhn3w4lpohwcqbl3@butterfly.localdomain> <20190521105256.GF219653@google.com> <20190521110030.GR32329@dhcp22.suse.cz> <20190521112423.GH219653@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521112423.GH219653@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 20:24:23, Minchan Kim wrote: > On Tue, May 21, 2019 at 01:00:30PM +0200, Michal Hocko wrote: > > On Tue 21-05-19 19:52:56, Minchan Kim wrote: > > > On Tue, May 21, 2019 at 09:06:38AM +0200, Oleksandr Natalenko wrote: > > > > Hi. > > > > > > > > On Tue, May 21, 2019 at 08:50:00AM +0200, Michal Hocko wrote: > > > > > On Tue 21-05-19 08:36:28, Oleksandr Natalenko wrote: > > > > > [...] > > > > > > Regarding restricting the hints, I'm definitely interested in having > > > > > > remote MADV_MERGEABLE/MADV_UNMERGEABLE. But, OTOH, doing it via remote > > > > > > madvise() introduces another issue with traversing remote VMAs reliably. > > > > > > IIUC, one can do this via userspace by parsing [s]maps file only, which > > > > > > is not very consistent, and once some range is parsed, and then it is > > > > > > immediately gone, a wrong hint will be sent. > > > > > > > > > > > > Isn't this a problem we should worry about? > > > > > > > > > > See http://lkml.kernel.org/r/20190520091829.GY6836@dhcp22.suse.cz > > > > > > > > Oh, thanks for the pointer. > > > > > > > > Indeed, for my specific task with remote KSM I'd go with map_files > > > > instead. This doesn't solve the task completely in case of traversal > > > > through all the VMAs in one pass, but makes it easier comparing to a > > > > remote syscall. > > > > > > I'm wondering how map_files can solve your concern exactly if you have > > > a concern about the race of vma unmap/remap even there are anonymous > > > vma which map_files doesn't support. > > > > See http://lkml.kernel.org/r/20190521105503.GQ32329@dhcp22.suse.cz > > Question is how it works for anonymous vma which don't have backing > file. We would have to export map_files like interface for anonymous vmas and have a way to invalidate on the VMA removal (reference counting or something similar), no question this will be some additional work to do. -- Michal Hocko SUSE Labs