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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20CE5C433F5 for ; Wed, 18 May 2022 12:12:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2170D6B0072; Wed, 18 May 2022 08:12:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1C49A6B0073; Wed, 18 May 2022 08:12:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 09AD56B0074; Wed, 18 May 2022 08:12:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id EAD736B0072 for ; Wed, 18 May 2022 08:12:32 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id B317E603D0 for ; Wed, 18 May 2022 12:12:32 +0000 (UTC) X-FDA: 79478751744.01.3E76ECB Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf24.hostedemail.com (Postfix) with ESMTP id AE4931800FB for ; Wed, 18 May 2022 12:12:21 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 8CFA121AEF; Wed, 18 May 2022 12:12:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1652875950; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qDlHrU3r3WkkvVR64fwd1Zr3oMvZyUV2mIKqOQiXpTE=; b=AnTgfMZm+3RaT1xBqSHySU0xpR8z7lq2slsyESumUNkucTTUUfFzpLg/M9vmdEToUrnwea AjcCs6WsxXEokyu+zhYyG1Oaz11rPQ2yt01Hcg6ojP5uuIzjr+2bDaH2KVZNPhwDYd0Gj0 Pqbo7FDUs75p0t4IKQq6U4inSjr/m8o= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id C375B2C141; Wed, 18 May 2022 12:12:29 +0000 (UTC) Date: Wed, 18 May 2022 14:12:26 +0200 From: Michal Hocko To: CGEL Cc: akpm@linux-foundation.org, ammarfaizi2@gnuweeb.org, oleksandr@natalenko.name, willy@infradead.org, linux-mm@kvack.org, corbet@lwn.net, linux-kernel@vger.kernel.org, xu xin , Yang Yang , Ran Xiaokai , wangyong , Yunkai Zhang , Jiang Xuexin , Hugh Dickins , linux-api@vger.kernel.org Subject: Re: [PATCH] mm/ksm: introduce ksm_enabled for each process Message-ID: References: <20220517092701.1662641-1-xu.xin16@zte.com.cn> <62845e2b.1c69fb81.cbf4a.1200@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <62845e2b.1c69fb81.cbf4a.1200@mx.google.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AE4931800FB X-Stat-Signature: fehi85yhe97s9446crg7pxhzft8mwnjh X-Rspam-User: Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=AnTgfMZm; spf=pass (imf24.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-HE-Tag: 1652875941-666163 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 Wed 18-05-22 02:47:06, CGEL wrote: > On Tue, May 17, 2022 at 04:04:38PM +0200, Michal Hocko wrote: > > [CCing Hugh and linux-api] > > > > On Tue 17-05-22 09:27:01, cgel.zte@gmail.com wrote: > > > From: xu xin > > > > > > For now, if we want to use KSM to merge pages of some apps, we have to > > > explicitly call madvise() in application code, which means installed > > > apps on OS needs to be uninstall and source code needs to be modified. > > > It is very inconvenient because sometimes users or app developers are not > > > willing to modify their app source codes for any reasons. > > Hello, Michal. > > > > Would it help to allow external control by process_madvise? > > > > Maybe, but it will be much more complicated to achieve this by > process_madvise(). process_madvise works on a serires of VMAs in > essential, So all the eligible VMAs have to be traversed. The problem > about this has been discussed in [1],[2]. > [1]https://lore.kernel.org/lkml/1835064.A2aMcgg3dW@natalenko.name/ > [2]https://lore.kernel.org/lkml/20220513133210.9dd0a4216bd8baaa1047562c@linux-foundation.org/ I can see that this is not a trivial interface to use but I do not think this would be too hard to be usable. There is certainly some coordination required between the external and the target tasks. But that is to be expected IMHO. You do not really want to configure merging without actually understanding what the application does and whether that is really OK. Right? Besides that, as far as I remember, the process_madvise interface doesn't really require exact vmas to be provided and a single range can span multiple VMAs. > > > So to use KSM more flexibly, we provide a new proc file "ksm_enabled" under > > > /proc//. We can pass parameter into this file with one of three values > > > as follows: > > > > > > always: > > > force all anonymous and eligible VMAs of this process to be > > > scanned by ksmd. > > > madvise: > > > the default state, unless user code call madvise, ksmd > > > doesn't scan this process. > > > never: > > > this process will never be scanned by ksmd and no merged > > > pages occurred in this process. > > > > > > With this patch, we can control KSM with ``/proc//ksm_enabled`` > > > based on every process. KSM for each process can be entirely disabled > > > (mostly for debugging purposes) or only enabled inside MADV_MERGEABLE > > > regions (to avoid the risk of consuming more cpu resources to scan for > > > ksmd) or enabled entirely for a process. > > > > I am not really familiar with KSM much but I am wondering whether the > > proc based interface is really the best fit. We have a very similar > > concern with THP where processes would like to override the global setup > > and that has been done with prctl interface. Is there any reason why > > this should be any different? > > > At least for now, I can't find a simpler implementation than proc file, > unless we add a new syscall used for changing another process mm's flag > in user space. What is the problem with the prctl extension? > Speaking to THP, the interactive UI of KSM is relatively simpler because > KSM dosen't have global knob like THP. OTOH, THP trades space for time > (consume memory) while KSM trades time for space (save memory), so THP > tends to be enabled system wide while KSM not. > > > Another question I have is about the interaction of the per-process > > tunable with any explicit madvise calls. AFAICS you have made this knob > > per mm but the actual implementation currently relies on the per-vma > > flags. That means that one can explicitly disallow merging by madvise > > for a range. Is it wise to override that by a per-process knob? I mean > > there might be a very good reason why a particular memory ranges should > > never be merged but a per-process knob could easily ignore that hint > > from the application. Or am I just confuse? > For now, there is no any hints for letting KSM never merge some memory > ranges. I am not sure I understand. Could you be more specific? -- Michal Hocko SUSE Labs