linux-kernel - Re: [PATCH -mm] cpuset,mm: fix no node to alloc memory when changing cpuset's mems

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Message-Id: <20100512003246.9f0ee03c.akpm@linux-foundation.org>
Date:	Wed, 12 May 2010 00:32:46 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	miaox@...fujitsu.com
Cc:	David Rientjes <rientjes@...gle.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>, Paul Menage <menage@...gle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH -mm] cpuset,mm: fix no node to alloc memory when
 changing cpuset's mems - fix2

On Wed, 12 May 2010 15:20:51 +0800 Miao Xie <miaox@...fujitsu.com> wrote:

> @@ -985,6 +984,7 @@ repeat:
>  	 * for the read-side.
>  	 */
>  	while (ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
> +		task_unlock(tsk);
>  		if (!task_curr(tsk))
>  			yield();
>  		goto repeat;

Oh, I meant to mention that.  No yield()s, please.  Their duration is
highly unpredictable.  Can we do something more deterministic here?

Did you consider doing all this with locking?  get_mems_allowed() does
mutex_lock(current->lock)?

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