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=-5.7 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 82BEFC5519F for ; Wed, 18 Nov 2020 19:32:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06AA4221FC for ; Wed, 18 Nov 2020 19:32:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="GHWJLGFH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726346AbgKRTcg (ORCPT ); Wed, 18 Nov 2020 14:32:36 -0500 Received: from mx2.suse.de ([195.135.220.15]:45126 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgKRTcg (ORCPT ); Wed, 18 Nov 2020 14:32:36 -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=1605727954; 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=qq+4RUIWTIRJUQsDUMjDphUgg4rSNzYU7mlJ5rkVEAA=; b=GHWJLGFHsuhg/s44OiNkL94AFNh0MLAJN9QkVvkm7T9NTz0yi+StlesXpSZ2D+xmtu5u33 auEJYHzr9zrA6MO2TkX6NP3P96NjtgiCeeaPL/9G08WkSicJlzsoY4npGdhg1N+4htBKRj hseLF8fZb2Tf/bBo6FZizbu09Yxij3Y= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 99EB7BDF3; Wed, 18 Nov 2020 19:32:34 +0000 (UTC) Date: Wed, 18 Nov 2020 20:32:33 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: Andrew Morton , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Christian Brauner , Oleg Nesterov , Tim Murray , linux-api@vger.kernel.org, linux-mm , LKML , kernel-team , Minchan Kim Subject: Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process Message-ID: <20201118193233.GV12284@dhcp22.suse.cz> References: <20201113173448.1863419-1-surenb@google.com> <20201113155539.64e0af5b60ad3145b018ab0d@linux-foundation.org> <20201113170032.7aa56ea273c900f97e6ccbdc@linux-foundation.org> <20201113171810.bebf66608b145cced85bf54c@linux-foundation.org> <20201113181632.6d98489465430a987c96568d@linux-foundation.org> <20201118154334.GT12284@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-api@vger.kernel.org On Wed 18-11-20 11:22:21, Suren Baghdasaryan wrote: > On Wed, Nov 18, 2020 at 11:10 AM Michal Hocko wrote: > > > > On Fri 13-11-20 18:16:32, Andrew Morton wrote: > > [...] > > > It's all sounding a bit painful (but not *too* painful). But to > > > reiterate, I do think that adding the ability for a process to shoot > > > down a large amount of another process's memory is a lot more generally > > > useful than tying it to SIGKILL, agree? > > > > I am not sure TBH. Is there any reasonable usecase where uncoordinated > > memory tear down is OK and a target process which is able to see the > > unmapped memory? > > I think uncoordinated memory tear down is a special case which makes > sense only when the target process is being killed (and we can enforce > that by allowing MADV_DONTNEED to be used only if the target process > has pending SIGKILL). That would be safe but then I am wondering whether it makes sense to implement as a madvise call. It is quite strange to expect somebody call a syscall on a killed process. But this is more a detail. I am not a great fan of a more generic MADV_DONTNEED on a remote process. This is just too dangerous IMHO. > However, the ability to apply other flavors of > process_madvise() to large memory areas spanning multiple VMAs can be > useful in more cases. Yes I do agree with that. The error reporting would be more tricky but I am not really sure that the exact reporting is really necessary for advice like interface. > For example in Android we will use > process_madvise(MADV_PAGEOUT) to "shrink" an inactive background > process. That makes sense to me. -- Michal Hocko SUSE Labs