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

[Michel Lespinasse]

On Tue, Oct 5, 2010 at 10:38 AM, Rik van Riel <riel@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
>
> 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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