linux-kernel - Re: [RFC, PATCHv2 0/2] mm: map few pages around fault address if they are in page cache

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Message-ID: <CA+55aFySHoOkTUDVpWPxq9PZtwXKxhS=Wz757fM7oyQazfKpfw@mail.gmail.com>
Date:	Tue, 18 Feb 2014 11:07:09 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Andi Kleen <ak@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	linux-mm <linux-mm@...ck.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCHv2 0/2] mm: map few pages around fault address if they
 are in page cache

On Tue, Feb 18, 2014 at 10:53 AM, Matthew Wilcox <willy@...ux.intel.com> wrote:
>
> Yes, I did mean "holepunches and page faults".  But here's the race I see:

Hmm. With truncate, we should be protected by i_size being changed
first (iirc - I didn't actually check), but I think you're right that
hole punching might race with a page being mapped at the same time.

> What I'm suggesting is going back to Kirill's earlier patch, but only
> locking the page with the highest index instead of all of the pages.
> truncate() will block on that page and then we'll notice that some or
> all of the other pages are also now past i_size and give up.

Actually, Kirill's latest patch seems to solve the problem with
locking - by simply never locking more than one page at a time. So I
guess it's all moot at least wrt the page preload..

          Linus
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