From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753156AbZBCWtb (ORCPT ); Tue, 3 Feb 2009 17:49:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752061AbZBCWtX (ORCPT ); Tue, 3 Feb 2009 17:49:23 -0500 Received: from smtp-out.google.com ([216.239.45.13]:55258 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751988AbZBCWtW (ORCPT ); Tue, 3 Feb 2009 17:49:22 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding: x-gmailtapped-by:x-gmailtapped; b=mtlZiXUqybgwNxCaBVzKfeLN25yqR2B7B79QaZeK/PiMUyoUHt6Yr9qGbkRogSMyM QWJ20zCb9+gT9Vx7gLVdQ== MIME-Version: 1.0 In-Reply-To: <20090203141645.91c7ea18.akpm@linux-foundation.org> References: <4976D77C.3020107@cn.fujitsu.com> <20090127144233.18cf9b3f.akpm@linux-foundation.org> <4987B925.1010405@cn.fujitsu.com> <20090203141645.91c7ea18.akpm@linux-foundation.org> Date: Tue, 3 Feb 2009 14:49:15 -0800 Message-ID: <6599ad830902031449j1fa3dd08re842b57f8700b389@mail.gmail.com> Subject: Re: [PATCH] cpuset: fix allocating page cache/slab object on the unallowed node when memory spread is set From: Paul Menage To: Andrew Morton Cc: miaox@cn.fujitsu.com, mingo@elte.hu, linux-kernel@vger.kernel.org, cl@linux-foundation.org, nickpiggin@yahoo.com.au Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-GMailtapped-By: 172.28.16.148 X-GMailtapped: menage Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 3, 2009 at 2:16 PM, Andrew Morton wrote: > On Tue, 03 Feb 2009 11:25:25 +0800 > Miao Xie wrote: > >> on 2009-1-28 6:42 Andrew Morton wrote: >> > On Wed, 21 Jan 2009 16:06:20 +0800 >> > Miao Xie wrote: >> > >> >> The task still allocated the page caches on old node after modifying its >> >> cpuset's mems when 'memory_spread_page' was set, it is caused by the old >> >> mem_allowed_list of the task, the current kernel doesn't updates it unless some >> >> function invokes cpuset_update_task_memory_state(), it is too late sometimes. >> >> We must update the mem_allowed_list of the tasks in time. >> >> >> >> Slab has the same problem. >> >> >> >> We fixes the bug by updating tasks' mem_allowed_list and spread flag after >> >> its cpuset's mems or spread flag is changed. >> >> >> >> >> >> ... >> >> >> >> --- a/kernel/kthread.c >> >> +++ b/kernel/kthread.c >> >> @@ -242,6 +242,7 @@ int kthreadd(void *unused) >> >> set_user_nice(tsk, KTHREAD_NICE_LEVEL); >> >> set_cpus_allowed_ptr(tsk, CPU_MASK_ALL_PTR); >> >> >> >> + current->mems_allowed = node_possible_map; >> >> current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG; >> > >> > Why this change? kthreadd() is called from rest_init(), before anyone >> > has had a chance to alter ->mems_allowed? >> >> I found that after mems_allowed of kthreadd was not initialized applying this patch, >> every bit of it is 1, so... >> Maybe it is redundant. > > I think it is redundant. kthreadd's mems_allowed _should_ be all-ones. > Or at least, all-nodes-allowed. > > I wasn't able to find out where the setting of init'smems_allowed > happens, after a bit of grepping and hunting. It should be done within > INIT_TASK, but isn't. > > Still, kthreadd is reliably parented by swapper, and there shold be no > need to alter its mems_allowed. > > Similarly, what was the reason for setting current->mems_allowed in > kernel_init()? That also should be unneeded. > > Finally, I've somewhat lost track of where we are with this patch. > Paul, do you see any other remaining issues? AFAICS this patch still has a race between a thread reading its mems_allowed, and another thread updating it. The current architecture of having task->mems_allowed be only updatable by current was PaulJ's code originally, and I'm a bit loathe to touch it. But if we're going to, we'll need at the minimum to add a lock for any code that touches current->mems_allowed. Paul