linux-kernel - Re: [PATCH 1/2] Allow GUP to fail instead of waiting on a page.

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Date:	Tue, 01 Feb 2011 11:48:20 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	avi@...hat.com, mtosatti@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] Allow GUP to fail instead of waiting on a page.

On 02/01/2011 06:21 AM, Gleb Natapov wrote:
> GUP user may want to try to acquire a reference to a page if it is already
> in memory, but not if IO, to bring it in, is needed. For example KVM may
> tell vcpu to schedule another guest process if current one is trying to
> access swapped out page. Meanwhile, the page will be swapped in and the
> guest process, that depends on it, will be able to run again.
>
> This patch adds FAULT_FLAG_RETRY_NOWAIT (suggested by Linus) and
> FOLL_NOWAIT follow_page flags. FAULT_FLAG_RETRY_NOWAIT, when used in
> conjunction with VM_FAULT_ALLOW_RETRY, indicates to handle_mm_fault that
> it shouldn't drop mmap_sem and wait on a page, but return VM_FAULT_RETRY
> instead.
>
> Signed-off-by: Gleb Natapov<gleb@...hat.com>
> CC: Linus Torvalds<torvalds@...ux-foundation.org>
> CC: Rik van Riel<riel@...hat.com>
> CC: Hugh Dickins<hughd@...gle.com>
> CC: Andrew Morton<akpm@...ux-foundation.org>

Acked-by: Rik van Riel <riel@...hat.com>

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