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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_DKIMWL_WL_HIGH, USER_AGENT_MUTT autolearn=ham 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 5684FC28CC2 for ; Fri, 31 May 2019 13:56:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FDE6269DD for ; Fri, 31 May 2019 13:56:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559310985; bh=0KfI7mpirsDEQB4YFaw+9JpeAIyIdzCLmeys0V7RWDI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Q3o4gICpJQV0lDh4iCQyeoBEn0iDnU6pDkiRdeFfluqggXxbHM70zX85QpgyDFcgT gYlInuinEq0z/fhm15nDbh3WT9urDYBug0LPbSdkQRqy/RlJg00OPL2qxY8kZokl5f 60xr0UMe1SppJ6Ykw7jlzGcBPp0R7oyfWA7P0b3k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726652AbfEaN4Y (ORCPT ); Fri, 31 May 2019 09:56:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:54376 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726386AbfEaN4X (ORCPT ); Fri, 31 May 2019 09:56:23 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 98465AF21; Fri, 31 May 2019 13:56:22 +0000 (UTC) Date: Fri, 31 May 2019 15:56:21 +0200 From: Michal Hocko To: Yang Shi Cc: Mel Gorman , Andrew Morton , "linux-mm@kvack.org" , linux-kernel Subject: Re: [HELP] How to get task_struct from mm Message-ID: <20190531135621.GR6896@dhcp22.suse.cz> References: <5cf71366-ba01-8ef0-3dbd-c9fec8a2b26f@linux.alibaba.com> <20190530154119.GF6703@dhcp22.suse.cz> <352de468-9091-9866-ccbd-10d80c25ebb4@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <352de468-9091-9866-ccbd-10d80c25ebb4@linux.alibaba.com> 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 Fri 31-05-19 20:51:05, Yang Shi wrote: > > > On 5/30/19 11:41 PM, Michal Hocko wrote: > > On Thu 30-05-19 14:57:46, Yang Shi wrote: > > > Hi folks, > > > > > > > > > As what we discussed about page demotion for PMEM at LSF/MM, the demotion > > > should respect to the mempolicy and allowed mems of the process which the > > > page (anonymous page only for now) belongs to. > > cpusets memory mask (aka mems_allowed) is indeed tricky and somehow > > awkward. It is inherently an address space property and I never > > understood why we have it per _thread_. This just doesn't make any > > sense to me. This just leads to weird corner cases. What should happen > > if different threads disagree about the allocation affinity while > > working on a shared address space? > > I'm supposed (just my guess) such restriction should just apply for the > first allocation. Just like memcg charge, who does it first, whose policy > gets applied. I am not really sure that was the deliberate design choice. Maybe somebody has a different recollection though. > > > The vma that the page is mapped to can be retrieved from rmap walk easily, > > > but we need know the task_struct that the vma belongs to. It looks there is > > > not such API, and container_of seems not work with pointer member. > > I do not think this is a good idea. As you point out in the reply we > > have that for memcgs but we really hope to get rid of mm->owner there > > as well. It is just more tricky there. Moreover such a reverse mapping > > would be incorrect. Just think of a disagreeing yet overlapping cpusets > > for different threads mapping the same page. > > > > Is it such a big deal to document that the node migrate is not > > compatible with cpusets? > > Not only cpuset, but get_vma_policy() also needs find task_struct from vma. > Currently, get_vma_policy() just uses "current", so it just returns the > current process's mempolicy if the vma doesn't have mempolicy. For the node > migrate case, "current" is definitely not correct. > > It looks there is not an easy way to workaround it unless we claim node > migrate is not compatible with both cpusets and mempolicy. yep, it seems so. -- Michal Hocko SUSE Labs