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[209.85.220.65]) by mx.google.com with SMTPS id l5sor2118747pjb.8.2019.05.28.01.13.59 for (Google Transport Security); Tue, 28 May 2019 01:13:59 -0700 (PDT) Received-SPF: pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=QCr0gmeD; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=jPe8elFZg7B9vxuD/4IJIpmknuctGjQlWuJbcfHCbZo=; b=QCr0gmeDfJ8l+4PZgPQmhrgvcsq7rzHJdu/mid5YMOaj4JJ71NK87f2a3UI5fHtizM NHxFErmUD2ddmqXSuEjyCzvbMzBKoPN/p+U23ASiPEdixURKcu8VoY/2Ev/YBvfMqksZ QmcDnDNrEpbGtu+TKYPUxYHMlKmoBAyTcjqANQ3FciqrFSQB+lnqOaeNvOhdidSuASLY ydSQdTU1Ygn/mhLIMpuV4rNp0P3dtoTE9Qn2zndwoAXIHZ1Fb7QmcsO1LbrVT1Zmbmmf 9Z+Kb7bVa9xCJhsT0yVvc2RfmIVMksVlSITkd3KvLtBhxdM94aOzzcieNUhcivcPeRhH bJSw== X-Google-Smtp-Source: APXvYqxz+7gV0cUm9BqW/w4lW7Rd07MflaO0RAjc5OfWacsw1ZnzegXi8JzOK4YSvfBvuMTUxWyASQ== X-Received: by 2002:a17:90a:77c4:: with SMTP id e4mr3969690pjs.86.1559031238720; Tue, 28 May 2019 01:13:58 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id y10sm18996551pfm.68.2019.05.28.01.13.54 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 28 May 2019 01:13:57 -0700 (PDT) Date: Tue, 28 May 2019 17:13:51 +0900 From: Minchan Kim To: Michal Hocko 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 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER Message-ID: <20190528081351.GA159710@google.com> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-8-minchan@kernel.org> <20190520092801.GA6836@dhcp22.suse.cz> <20190521025533.GH10039@google.com> <20190521062628.GE32329@dhcp22.suse.cz> <20190527075811.GC6879@google.com> <20190527124411.GC1658@dhcp22.suse.cz> <20190528032632.GF6879@google.com> <20190528062947.GL1658@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190528062947.GL1658@dhcp22.suse.cz> 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, May 28, 2019 at 08:29:47AM +0200, Michal Hocko wrote: > On Tue 28-05-19 12:26:32, Minchan Kim wrote: > > On Mon, May 27, 2019 at 02:44:11PM +0200, Michal Hocko wrote: > > > On Mon 27-05-19 16:58:11, Minchan Kim wrote: > > > > On Tue, May 21, 2019 at 08:26:28AM +0200, Michal Hocko wrote: > > > > > On Tue 21-05-19 11:55:33, Minchan Kim wrote: > > > > > > On Mon, May 20, 2019 at 11:28:01AM +0200, Michal Hocko wrote: > > > > > > > [cc linux-api] > > > > > > > > > > > > > > On Mon 20-05-19 12:52:54, Minchan Kim wrote: > > > > > > > > System could have much faster swap device like zRAM. In that case, swapping > > > > > > > > is extremely cheaper than file-IO on the low-end storage. > > > > > > > > In this configuration, userspace could handle different strategy for each > > > > > > > > kinds of vma. IOW, they want to reclaim anonymous pages by MADV_COLD > > > > > > > > while it keeps file-backed pages in inactive LRU by MADV_COOL because > > > > > > > > file IO is more expensive in this case so want to keep them in memory > > > > > > > > until memory pressure happens. > > > > > > > > > > > > > > > > To support such strategy easier, this patch introduces > > > > > > > > MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER options in madvise(2) like > > > > > > > > that /proc//clear_refs already has supported same filters. > > > > > > > > They are filters could be Ored with other existing hints using top two bits > > > > > > > > of (int behavior). > > > > > > > > > > > > > > madvise operates on top of ranges and it is quite trivial to do the > > > > > > > filtering from the userspace so why do we need any additional filtering? > > > > > > > > > > > > > > > Once either of them is set, the hint could affect only the interested vma > > > > > > > > either anonymous or file-backed. > > > > > > > > > > > > > > > > With that, user could call a process_madvise syscall simply with a entire > > > > > > > > range(0x0 - 0xFFFFFFFFFFFFFFFF) but either of MADV_ANONYMOUS_FILTER and > > > > > > > > MADV_FILE_FILTER so there is no need to call the syscall range by range. > > > > > > > > > > > > > > OK, so here is the reason you want that. The immediate question is why > > > > > > > cannot the monitor do the filtering from the userspace. Slightly more > > > > > > > work, all right, but less of an API to expose and that itself is a > > > > > > > strong argument against. > > > > > > > > > > > > What I should do if we don't have such filter option is to enumerate all of > > > > > > vma via /proc//maps and then parse every ranges and inode from string, > > > > > > which would be painful for 2000+ vmas. > > > > > > > > > > Painful is not an argument to add a new user API. If the existing API > > > > > suits the purpose then it should be used. If it is not usable, we can > > > > > think of a different way. > > > > > > > > I measured 1568 vma parsing overhead of /proc//maps in ARM64 modern > > > > mobile CPU. It takes 60ms and 185ms on big cores depending on cpu governor. > > > > It's never trivial. > > > > > > This is not the only option. Have you tried to simply use > > > /proc//map_files interface? This will provide you with all the file > > > backed mappings. > > > > I compared maps vs. map_files with 3036 file-backed vma. > > Test scenario is to dump all of vmas of the process and parse address > > ranges. > > For map_files, it's easy to parse each address range because directory name > > itself is range. However, in case of maps, I need to parse each range > > line by line so need to scan all of lines. > > > > (maps cover additional non-file-backed vmas so nr_vma is a little bigger) > > > > performance mode: > > map_files: nr_vma 3036 usec 13387 > > maps : nr_vma 3078 usec 12923 > > > > powersave mode: > > > > map_files: nr_vma 3036 usec 52614 > > maps : nr_vma 3078 usec 41089 > > > > map_files is slower than maps if we dump all of vmas. I guess directory > > operation needs much more jobs(e.g., dentry lookup, instantiation) > > compared to maps. > > OK, that is somehow surprising. I am still not convinced the filter is a > good idea though. The primary reason is that it encourages using madvise > on a wide range without having a clue what the range contains. E.g. the > full address range and rely the right thing will happen. Do we really > want madvise to operate in that mode? If user space daemon(e.g., activity manager service) could know a certain process is bakground and idle for a while, yeb, that would be good option. > > Btw. if we went with the per vma fd approach then you would get this > feature automatically because map_files would refer to file backed > mappings while map_anon could refer only to anonymous mappings. The reason to add such filter option is to avoid the parsing overhead so map_anon wouldn't be helpful. > > -- > Michal Hocko > SUSE Labs