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=-11.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 4557FC4741F for ; Thu, 5 Nov 2020 17:21:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CD8252072E for ; Thu, 5 Nov 2020 17:21:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="MUimO6Mb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731558AbgKERV0 (ORCPT ); Thu, 5 Nov 2020 12:21:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730975AbgKERV0 (ORCPT ); Thu, 5 Nov 2020 12:21:26 -0500 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0BA6C0613CF for ; Thu, 5 Nov 2020 09:21:25 -0800 (PST) Received: by mail-wm1-x344.google.com with SMTP id s13so2374417wmh.4 for ; Thu, 05 Nov 2020 09:21:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=jVksYP+m1csAgSVkfxG7oivUT+KEbcTMSnmWbNLe2cc=; b=MUimO6Mb7ah6cGTZAmJxgooDhnJYtCO+v11DToWUnLcnKBgIS9B522rXKjCeF//gj2 P76Jx9NUMKepJIh5rbuSlFCSgBBpc9RjIE8OkFffh8b3OYLIXYZkS2dGcEQC+LREixDB 8ZU0UMvyXJvyy9VP5x4hFCURmF4K4JWeGoKG87nvzf22wQUHBUkFFSsQUhPlTD3fCb/3 +wgtioTDDpSjPOc/SpMBfrsfQGo+vFANxMb3Z8CAE9MAkWCWSFbB5eOC34x4BYcwvi5b y4G/hLMtTcGr3et8Dc6KcQdALXq3+Pz/huUYBFc3y/Mc+65JJ7y4JPT4wEoGkz3TXOu2 HFhw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=jVksYP+m1csAgSVkfxG7oivUT+KEbcTMSnmWbNLe2cc=; b=CKURkz2Boc8uy2ViNdpOKiLqda7IFz8eeCaR/7ahLoHfahCXuqBouain+NJ7whJIfd xZfRk4XIejLb0Kgxag8NYHPf1atj+JSu8A5ozDzCx3ZDDXfEOokkOuPbUpg5SFGi0J+l a3WBzeJKqamlj+hLviu51tjIg30lrM6sqf1UemJUkd8m966eL9ggYzL0wOsMjA3T+DZS YazfysBax2I1hz0sQR0j+h8Hn9hOtHUezg9umpq9MKWY2p7MaFXQQaAM2Ogamgce8D40 2fKF7e4VRnGHoxn3DdAFehi1nwvvn0JCFf/7OKuqROrLFmug5rp8SmPjfPm+F2NWWeVc iI/Q== X-Gm-Message-State: AOAM533JVvXheLe7VmeSw4nxpDmdf7Lyvyr1hwWFKVBeudatid0pfCKr nPekuuV+wT/Q6R9tgLOTKAhml24qdM2RlrNS1yWq3g== X-Google-Smtp-Source: ABdhPJwHMg6G//mLKaUG+ayZ/oBbHYiilTcQrDw6mInR9JdkQpyrnKlQ8b/n+2t4gyudsR/O/qG576iUthD6ZFtCukg= X-Received: by 2002:a1c:7c0e:: with SMTP id x14mr3869550wmc.88.1604596884421; Thu, 05 Nov 2020 09:21:24 -0800 (PST) MIME-Version: 1.0 References: <20201015092030.GB22589@dhcp22.suse.cz> <20201103093550.GE21990@dhcp22.suse.cz> <20201103213228.GB1631979@google.com> <20201104065844.GM21990@dhcp22.suse.cz> <20201104204051.GA3544305@google.com> <20201105122012.GD21348@dhcp22.suse.cz> <20201105171611.GO21348@dhcp22.suse.cz> In-Reply-To: <20201105171611.GO21348@dhcp22.suse.cz> From: Suren Baghdasaryan Date: Thu, 5 Nov 2020 09:21:13 -0800 Message-ID: Subject: Re: [RFC]: userspace memory reaping To: Michal Hocko Cc: Minchan Kim , linux-api@vger.kernel.org, linux-mm , Andrew Morton , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Christian Brauner , Oleg Nesterov , Tim Murray , kernel-team , LKML , Mel Gorman Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Nov 5, 2020 at 9:16 AM Michal Hocko wrote: > > On Thu 05-11-20 08:50:58, Suren Baghdasaryan wrote: > > On Thu, Nov 5, 2020 at 4:20 AM Michal Hocko wrote: > > > > > > On Wed 04-11-20 12:40:51, Minchan Kim wrote: > > > > On Wed, Nov 04, 2020 at 07:58:44AM +0100, Michal Hocko wrote: > > > > > On Tue 03-11-20 13:32:28, Minchan Kim wrote: > > > > > > On Tue, Nov 03, 2020 at 10:35:50AM +0100, Michal Hocko wrote: > > > > > > > On Mon 02-11-20 12:29:24, Suren Baghdasaryan wrote: > > > > > > > [...] > > > > > > > > To follow up on this. Should I post an RFC implementing SIGKILL_SYNC > > > > > > > > which in addition to sending a kill signal would also reap the > > > > > > > > victim's mm in the context of the caller? Maybe having some code will > > > > > > > > get the discussion moving forward? > > > > > > > > > > > > > > Yeah, having a code, even preliminary, might help here. This definitely > > > > > > > needs a good to go from process management people as that proper is land > > > > > > > full of surprises... > > > > > > > > > > > > Just to remind a idea I suggested to reuse existing concept > > > > > > > > > > > > fd = pidfd_open(victim process) > > > > > > fdatasync(fd); > > > > > > close(fd); > > > > > > > > > > I must have missed this proposal. Anyway, are you suggesting fdatasync > > > > > to act as a destructive operation? > > > > > > > > write(fd) && fdatasync(fd) are already destructive operation if the file > > > > is shared. > > > > > > I am likely missing something because fdatasync will not destroy any > > > underlying data. It will sync > > > > > > > You don't need to reaping as destruptive operation. Rather than, just > > > > commit on the asynchrnous status "write file into page cache and commit > > > > with fsync" and "killing process and commit with fsync". > > > > > > I am sorry but I do not follow. The result of the memory reaping is a > > > data loss. Any private mapping will simply lose it's content. The caller > > > will get EFAULT when trying to access it but there is no way to > > > reconstruct the data. This is everything but not resembling what I see > > > f{data}sync is used for. > > > > I think Minchan considers f{data}sync as a "commit" operation. > > But there is nothing like commit in that operation. It is simply a > destroy operation. ftruncate as Minchan mentions in another reply would > be a closer fit but how do you interpret the length argument? What about > memory regions which cannot be reaped? > > I do understand that reusing an existing mechanism is usually preferable > but the semantic should be reasonable and easy to reason about. Maybe then we can consider a flag for pidfd_send_signal() to indicate that we want a synchronous mm cleanup when SIGKILL is being sent? Similar to my original RFC but cleanup would happen in the context of the caller. That seems to me like the simplest and most obvious way of expressing what we want to accomplish. WDYT? > > -- > Michal Hocko > SUSE Labs > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >