From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758197Ab0EDKxN (ORCPT ); Tue, 4 May 2010 06:53:13 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:55457 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752987Ab0EDKxJ (ORCPT ); Tue, 4 May 2010 06:53:09 -0400 Message-ID: <4BDFFCB9.5010402@cn.fujitsu.com> Date: Tue, 04 May 2010 18:53:45 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4 MIME-Version: 1.0 To: David Rientjes CC: Lee Schermerhorn , Nick Piggin , Paul Menage , Andrew Morton , Linux-Kernel , Linux-MM Subject: Re: [PATCH 1/2] mm: fix bugs of mpol_rebind_nodemask() References: <4BD05929.8040900@cn.fujitsu.com> <4BD0F797.6020704@cn.fujitsu.com> <4BD90529.3090401@cn.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org on 2010-4-30 2:03, David Rientjes wrote: > On Thu, 29 Apr 2010, Miao Xie wrote: > >>> That's been the behavior for at least three years so changing it from >>> under the applications isn't acceptable, see >>> Documentation/vm/numa_memory_policy.txt regarding mempolicy rebinds and >>> the two flags that are defined that can be used to adjust the behavior. >> >> Is the flags what you said MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES? >> But the codes that I changed isn't under MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES. >> The documentation doesn't say what we should do if either of these two flags is not set. >> > > MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES allow you to adjust the > behavior of the rebind: the former requires specific nodes to be assigned > to the mempolicy and could suppress the rebind completely, if necessary; > the latter ensures the mempolicy nodemask has a certain weight as nodes > are assigned in a round-robin manner. The behavior that you're referring > to is provided via MPOL_F_RELATIVE_NODES, which guarantees whatever weight > is passed via set_mempolicy() will be preserved when mems are added to a > cpuset. > > Regardless of whether the behavior is documented when either flag is > passed, we can't change the long-standing default behavior that people use > when their cpuset mems are rebound: we can only extend the functionality > and the behavior you're seeking is already available with a > MPOL_F_RELATIVE_NODES flag modifier. > >> Furthermore, in order to fix no node to alloc memory, when we want to update mempolicy >> and mems_allowed, we expand the set of nodes first (set all the newly nodes) and >> shrink the set of nodes lazily(clean disallowed nodes). > > That's a cpuset implementation choice, not a mempolicy one; mempolicies > have nothing to do with an empty current->mems_allowed. > >> But remap() breaks the expanding, so if we don't remove remap(), the problem can't be >> fixed. Otherwise, cpuset has to do the rebinding by itself and the code is ugly. >> Like this: >> >> static void cpuset_change_task_nodemask(struct task_struct *tsk, nodemask_t *newmems) >> { >> nodemask_t tmp; >> ... >> /* expand the set of nodes */ >> if (!mpol_store_user_nodemask(tsk->mempolicy)) { >> nodes_remap(tmp, ...); >> nodes_or(tsk->mempolicy->v.nodes, tsk->mempolicy->v.nodes, tmp); >> } >> ... >> >> /* shrink the set of nodes */ >> if (!mpol_store_user_nodemask(tsk->mempolicy)) >> tsk->mempolicy->v.nodes = tmp; >> } >> > > I don't see why this is even necessary, the mempolicy code could simply > return numa_node_id() when nodes_empty(current->mempolicy->v.nodes) to > close the race. > > [ Your pseudo-code is also lacking task_lock(tsk), which is required to > safely dereference tsk->mempolicy, and this is only available so far in > -mm since the oom killer rewrite. ] I updated it and remade a new patchset, could you review it for me? Thanks Miao