linux-kernel - Re: [PATCH 1/6] mlock: only hold mmap_sem in shared mode when faulting in pages

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Message-ID: <AANLkTinY0pcTcd+OxPLyvsJgHgh=cTaB1-8VbEA2tstb@mail.gmail.com>
Date:	Thu, 9 Dec 2010 22:11:30 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Nick Piggin <npiggin@...nel.dk>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/6] mlock: only hold mmap_sem in shared mode when
 faulting in pages

On Wednesday, December 8, 2010, Michel Lespinasse <walken@...gle.com> wrote:
>
> Yes, patch 1/6 changes the long hold time to be in read mode instead
> of write mode, which is only a band-aid. But, this prepares for patch
> 5/6, which releases mmap_sem whenever there is contention on it or
> when blocking on disk reads.

I have to say that I'm not a huge fan of that horribly kludgy
contention check case.

The "move page-in to read-locked sequence" and the changes to
get_user_pages look fine, but the contention thing is just disgusting.
I'd really like to see some other approach if at all possible.
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