linux-kernel - Re: [PATCH 2/3] Retry page fault when blocking on disk transfer.

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Message-ID: <AANLkTimdACZ9Xm01DM2+E64+T5XfLffrkFBhf7CJ286p@mail.gmail.com>
Date:	Tue, 5 Oct 2010 15:44:22 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	Ying Han <yinghan@...gle.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] Retry page fault when blocking on disk transfer.

On Tue, Oct 5, 2010 at 10:38 AM, Rik van Riel <riel@...hat.com> wrote:
> On 10/05/2010 03:53 AM, Michel Lespinasse wrote:
>>
>> This change reduces mmap_sem hold times that are caused by waiting for
>> disk transfers when accessing file mapped VMAs. It introduces the
>> VM_FAULT_ALLOW_RETRY flag, which indicates that the call site wants
>> mmap_sem to be released if blocking on a pending disk transfer.
>> In that case, filemap_fault() returns the VM_FAULT_RETRY status bit
>> and do_page_fault() will then re-acquire mmap_sem and retry the page
>> fault.
>> It is expected that the retry will hit the same page which will now be
>> cached, and thus it will complete with a low mmap_sem hold time.
>>
>> Signed-off-by: Michel Lespinasse<walken@...gle.com>
>
> Acked-by: Rik van Riel <riel@...hat.com>
>
> Looks like it should be relatively easy to do something
> similar in do_swap_page also.

Good idea. We don't make use of swap too much, which is probably why
we didn't have that in our kernel, but it seems like a good idea just
for uniformity. I'll add this in a follow-on patch.

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