From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: * X-Spam-Status: No, score=1.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F609C282CE for ; Tue, 4 Jun 2019 04:27:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4EE8124C78 for ; Tue, 4 Jun 2019 04:27:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559622421; bh=6aFzgm9Rt3pEKISGvvVto5BXM8ePj6Txu3OHhO90M5c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=DoCfhpAGsCfn05OS2SDP+pwaDmSW2+uvlHQAjr3pAyvMDhKj24JLMFE5NKZfbDlMh yUUvGraqcCKGnb8ogaYUUZ8/EoulszvDmhp5qrhxZQZRWWcgQLhg2a7VGanh2bPxf+ 4V78Tj8pEeS6dlOjQ7kPWs+S51AMjA60zr87E3DM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726535AbfFDE1A (ORCPT ); Tue, 4 Jun 2019 00:27:00 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:43772 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726078AbfFDE1A (ORCPT ); Tue, 4 Jun 2019 00:27:00 -0400 Received: by mail-pg1-f196.google.com with SMTP id f25so9545965pgv.10; Mon, 03 Jun 2019 21:26:59 -0700 (PDT) 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=5ghW7vZxtD9TEM+qgoDG0MODtbI6VDLCCfPNHey69jA=; b=GGLOY4Lh3Uc5kASC5eWRsdjBzWNIdVe64631KWVwKmllcALTogaSgWf1MfDyArRuto SY0qwlS9eNnEro/DclKyuFoVITC030558nEHdOsh8EPAvnas61psi+E06QK9wsQdwscy 9jrOP9iCsqxqKVvMAZb9jxOaw/PqtjOubFI50yvxBoTtP0wa75b0Gqqv13b7hT5UsbUZ +Vi0h1EFkIcPi4aIDl4Fb2SLlJRRe1VImbiK5lnjdJ/kmQMwFDPBztoan5MFomGDORfT OtDoC9ekgw8rFKXJQQEyFzvKYwwZZitO6Ov83a0yn8GzO3F5hVHoEvfJ3YoM0p1wxef0 mfWg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=5ghW7vZxtD9TEM+qgoDG0MODtbI6VDLCCfPNHey69jA=; b=YkyPZISQTO2AvuUaKHoDukszSkrtO2rie7VgouX+ZBWvPY+jtzf+VNSYk8uII4CNEX FXFfxcmZmmXts4FJWF1KeMgoWRe1IfxgPGLaTmKlJBsvXNxBZMSt6Ixd38HkwubYtc4D Kh15Y3pu82lqA31LsSwN2vMp+pa7Z8LaHkBs3+VWMwX6b0pbY2PJcdzQZDNSMaPXeEmj kLuCvvHDNV4FYiPdDs+8n8jh80XRFtJETAI/66tYK0VmBsmJBjbn9avtm+SDUWFghLXz E5aX/0NWZVhlnhmSqPHV2sp/v6/1MaYiXHETgP/PQeH52wxb3lKZWLxjf4Mat56V7cDO Dbdg== X-Gm-Message-State: APjAAAX96P945bYmMKidiJe5X4jkeJJDFCeYTL0soZNbqabX+tCJGvzj 7ykYtM2ruXZQ4jsNSnb4vYo= X-Google-Smtp-Source: APXvYqxAEyGDKuJIqda0JeMfwT8/ZDr6kjeGAWrJ14wxIzxTTOjbDVn6f7FM0zC8JcZTmxqn6bLclA== X-Received: by 2002:a63:e10d:: with SMTP id z13mr11914157pgh.116.1559622419276; Mon, 03 Jun 2019 21:26:59 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id m11sm13287492pjv.21.2019.06.03.21.26.54 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 03 Jun 2019 21:26:58 -0700 (PDT) Date: Tue, 4 Jun 2019 13:26:51 +0900 From: Minchan Kim To: Michal Hocko Cc: Andrew Morton , linux-mm , LKML , linux-api@vger.kernel.org, Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , jannh@google.com, oleg@redhat.com, christian@brauner.io, oleksandr@redhat.com, hdanton@sina.com Subject: Re: [RFCv2 1/6] mm: introduce MADV_COLD Message-ID: <20190604042651.GC43390@google.com> References: <20190531064313.193437-1-minchan@kernel.org> <20190531064313.193437-2-minchan@kernel.org> <20190531084752.GI6896@dhcp22.suse.cz> <20190531133904.GC195463@google.com> <20190531140332.GT6896@dhcp22.suse.cz> <20190531143407.GB216592@google.com> <20190603071607.GB4531@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190603071607.GB4531@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 03, 2019 at 09:16:07AM +0200, Michal Hocko wrote: > On Fri 31-05-19 23:34:07, Minchan Kim wrote: > > On Fri, May 31, 2019 at 04:03:32PM +0200, Michal Hocko wrote: > > > On Fri 31-05-19 22:39:04, Minchan Kim wrote: > > > > On Fri, May 31, 2019 at 10:47:52AM +0200, Michal Hocko wrote: > > > > > On Fri 31-05-19 15:43:08, Minchan Kim wrote: > > > > > > When a process expects no accesses to a certain memory range, it could > > > > > > give a hint to kernel that the pages can be reclaimed when memory pressure > > > > > > happens but data should be preserved for future use. This could reduce > > > > > > workingset eviction so it ends up increasing performance. > > > > > > > > > > > > This patch introduces the new MADV_COLD hint to madvise(2) syscall. > > > > > > MADV_COLD can be used by a process to mark a memory range as not expected > > > > > > to be used in the near future. The hint can help kernel in deciding which > > > > > > pages to evict early during memory pressure. > > > > > > > > > > > > Internally, it works via deactivating pages from active list to inactive's > > > > > > head if the page is private because inactive list could be full of > > > > > > used-once pages which are first candidate for the reclaiming and that's a > > > > > > reason why MADV_FREE move pages to head of inactive LRU list. Therefore, > > > > > > if the memory pressure happens, they will be reclaimed earlier than other > > > > > > active pages unless there is no access until the time. > > > > > > > > > > [I am intentionally not looking at the implementation because below > > > > > points should be clear from the changelog - sorry about nagging ;)] > > > > > > > > > > What kind of pages can be deactivated? Anonymous/File backed. > > > > > Private/shared? If shared, are there any restrictions? > > > > > > > > Both file and private pages could be deactived from each active LRU > > > > to each inactive LRU if the page has one map_count. In other words, > > > > > > > > if (page_mapcount(page) <= 1) > > > > deactivate_page(page); > > > > > > Why do we restrict to pages that are single mapped? > > > > Because page table in one of process shared the page would have access bit > > so finally we couldn't reclaim the page. The more process it is shared, > > the more fail to reclaim. > > So what? In other words why should it be restricted solely based on the > map count. I can see a reason to restrict based on the access > permissions because we do not want to simplify all sorts of side channel > attacks but memory reclaim is capable of reclaiming shared pages and so > far I haven't heard any sound argument why madvise should skip those. > Again if there are any reasons, then document them in the changelog. I will go with removing the part so that defer to decision to the VM reclaim based on the review. > > [...] > > > > Please document this, if this is really a desirable semantic because > > > then you have the same set of problems as we've had with the early > > > MADV_FREE implementation mentioned above. > > > > IIRC, the problem of MADV_FREE was that we couldn't discard freeable > > pages because VM never scan anonymous LRU with swapless system. > > However, it's not the our case because we should reclaim them, not > > discarding. > > Right. But there is still the page cache reclaim. Is it expected that > an explicitly cold memory doesn't get reclaimed because we have a > sufficient amount of page cache (a very common case) and we never age > anonymous memory because of that? If there are lots of used-once pages in file-LRU, I think there is no need to reclaim anonymous pages because it needs bigger overhead due to IO. It has been true for a long time in current VM policy. Reclaim preference model based on hints is as following based on cost: MADV_DONTNEED >> MADV_PAGEOUT > used-once pages > MADV_FREE >= MADV_COLD It is desirable for the new hints to be placed in the reclaiming preference order such that a) they don't overlap functionally with existing hints and b) we have a balanced ordering of disruptive and non-disruptive hints.