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

On Tue, Feb 18, 2014 at 10:53 AM, Matthew Wilcox <willy@linux.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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