linux-kernel - Re: [PATCH 00/11] V4: rwsem changes + down_read

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Message-ID: <AANLkTikbeXjmRW4gqiy1Ss-Suce5gIM4xJ5o9Z81ZTQX@mail.gmail.com>
Date:	Tue, 25 May 2010 02:12:14 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 00/11] V4: rwsem changes + down_read_critical() proposal

On Tue, May 25, 2010 at 1:47 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> So what happened to those patches that dropped mmap_sem during I/O?

Yes, we do have patches trying to release the mmap_sem when a page
fault for a file backed VMA blocks on accessing the corresponding
file. We have not given up on these, and we intend to try submitting
them again. However, these patches do *not* address the case of a page
fault blocking while trying to get a free page (i.e. when you get
under high memory pressure).

> I really don't like people tinkering with the lock implementations like
> this. Nor do I like the naming, stats are in no way _critical_.

Critical here refers to the fact that you're not allowed to block
while holding the unfairly acquired rwsem.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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