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SubjectRe: [PATCH 2/3] Retry page fault when blocking on disk transfer.
On 10/08/2010 12:39 AM, Michel Lespinasse wrote:
> On Tue, Oct 05, 2010 at 03:44:22PM -0700, Michel Lespinasse wrote:
>> On Tue, Oct 5, 2010 at 10:38 AM, Rik van Riel<riel@redhat.com> wrote:
>>> 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.
>
> So here's the patch. Sorry for the delay - it did not take long to write,
> but I couldn't test it before today.
>
> Please have a look - I'd like to add this to the series I sent earlier.
>
> ----------------------------------- 8< ---------------------------------
>
> Retry page fault when blocking on swap in
>
> This change is the cousin of 'Retry page fault when blocking
> on disk transfer'. The idea here is to reduce mmap_sem hold times
> that are caused by disk transfers when swapping in pages. We drop
> mmap_sem while waiting for the page lock, and return the VM_FAULT_RETRY
> flag. do_page_fault will then re-acquire mmap_sem and retry the
> page fault. It is expected that upon retry the page will now be cached,
> and thus the retry will complete with a low mmap_sem hold time.
>
> Signed-off-by: Michel Lespinasse<walken@google.com>
>
> diff --git a/mm/memory.c b/mm/memory.c
> index b068c68..0ec70b4 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2613,6 +2613,21 @@ int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end)
> return 0;
> }
>
> +static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
> + unsigned int flags)
> +{
> + if (trylock_page(page))
> + return 1;
> + if (!(flags& FAULT_FLAG_ALLOW_RETRY)) {
> + __lock_page(page);
> + return 1;
> + }
> +
> + up_read(&mm->mmap_sem);
> + wait_on_page_locked(page);
> + return 0;
> +}

Wait a moment. Your other patch 2/3 also has a
lock_page_or_retry function. That one is in
filemap.c and takes slightly different arguments,
to do essentially the same thing...

+/*
+ * Lock the page, unless this would block and the caller indicated that it
+ * can handle a retry.
+ */
+static int lock_page_or_retry(struct page *page,
+ struct vm_area_struct *vma, struct vm_fault *vmf)
+{

Is there a way the two functions can be merged
into one?

--
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