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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AB2FBC4741F for ; Thu, 5 Nov 2020 17:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53CF92151B for ; Thu, 5 Nov 2020 17:16:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="GKVrtwDW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729862AbgKERQR (ORCPT ); Thu, 5 Nov 2020 12:16:17 -0500 Received: from mx2.suse.de ([195.135.220.15]:54598 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728523AbgKERQP (ORCPT ); Thu, 5 Nov 2020 12:16:15 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1604596573; h=from:from:reply-to:subject:subject: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=iSIQtjhr10//VD1ePr+4g1ncowxf9ZrRXex0wWZq72I=; b=GKVrtwDWxpqYR0Co35DPMPeKUWx8jjDTMPfP5GQcq39XUodVa5mb+N93C5ijnaLAOA1hgF hbbzCm7XVqMyUC81jqyRjVxt1/ObnbW4UOc3lA54s9j7K+alvBF01QUrDHyUecnaOKL0lt fXRqzLiviOJN2CjcuNEvHkZnCA/D6LY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 05CB0ABAE; Thu, 5 Nov 2020 17:16:13 +0000 (UTC) Date: Thu, 5 Nov 2020 18:16:11 +0100 From: Michal Hocko To: Suren Baghdasaryan 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 Subject: Re: [RFC]: userspace memory reaping Message-ID: <20201105171611.GO21348@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Michal Hocko SUSE Labs