linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Message-ID: <alpine.DEB.2.00.0912171331300.3638@router.home>
Date:	Thu, 17 Dec 2009 13:33:01 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>, minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

On Thu, 17 Dec 2009, Andi Kleen wrote:

> > There are a few interesting cases like stack extention and hugetlbfs,
> > but I think we could start by falling back to mmap_sem locked behaviour
> > if the speculative thing fails.
>
> You mean fall back to mmap_sem if anything sleeps? Maybe. Would need
> to check how many such points are really there.

You always need some reference on the mm_struct (mm_read_lock) if you are
going to sleep to ensure that mm_struct still exists after waking up (page
fault, page allocation). RCU and other spin locks are not helping there.

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