From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 994B96B0224 for ; Thu, 29 Apr 2010 14:03:35 -0400 (EDT) Received: from wpaz5.hot.corp.google.com (wpaz5.hot.corp.google.com [172.24.198.69]) by smtp-out.google.com with ESMTP id o3TI3U6c006887 for ; Thu, 29 Apr 2010 11:03:30 -0700 Received: from pzk39 (pzk39.prod.google.com [10.243.19.167]) by wpaz5.hot.corp.google.com with ESMTP id o3TI3RUs011483 for ; Thu, 29 Apr 2010 11:03:29 -0700 Received: by pzk39 with SMTP id 39so3109633pzk.7 for ; Thu, 29 Apr 2010 11:03:27 -0700 (PDT) Date: Thu, 29 Apr 2010 11:03:21 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH 1/2] mm: fix bugs of mpol_rebind_nodemask() In-Reply-To: <4BD90529.3090401@cn.fujitsu.com> Message-ID: References: <4BD05929.8040900@cn.fujitsu.com> <4BD0F797.6020704@cn.fujitsu.com> <4BD90529.3090401@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Miao Xie Cc: Lee Schermerhorn , Nick Piggin , Paul Menage , Andrew Morton , Linux-Kernel , Linux-MM List-ID: 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. ] -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org