Re: [PATCH v2] fix __set_page_dirty_no_writeback() return value

[Bob Liu <lliubbo@gmail.com>]

On Thu, Nov 11, 2010 at 11:45 AM, Wu Fengguang <fengguang.wu@intel.com> wrote:
> On Thu, Nov 11, 2010 at 11:36:48AM +0800, Bob Liu wrote:
>> On Thu, Nov 11, 2010 at 11:26 AM, Wu Fengguang <fengguang.wu@intel.com> wrote:
>> > On Thu, Nov 11, 2010 at 11:05:54AM +0800, Bob Liu wrote:
>> >> __set_page_dirty_no_writeback() should return true if it actually transitioned
>> >> the page from a clean to dirty state although it seems nobody used its return
>> >> value now.
>> >>
>> >> Change from v1:
>> >>       * preserving cacheline optimisation as Andrew pointed out
>> >>
>> >> Signed-off-by: Bob Liu <lliubbo@gmail.com>
>> >> ---
>> >>  mm/page-writeback.c |    4 +++-
>> >>  1 files changed, 3 insertions(+), 1 deletions(-)
>> >>
>> >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> >> index bf85062..ac7018a 100644
>> >> --- a/mm/page-writeback.c
>> >> +++ b/mm/page-writeback.c
>> >> @@ -1157,8 +1157,10 @@ EXPORT_SYMBOL(write_one_page);
>> >>   */
>> >>  int __set_page_dirty_no_writeback(struct page *page)
>> >>  {
>> >> -     if (!PageDirty(page))
>> >> +     if (!PageDirty(page)) {
>> >>               SetPageDirty(page);
>> >> +             return 1;
>> >> +     }
>> >>       return 0;
>> >>  }
>> >
>> > It's still racy if not using TestSetPageDirty(). In fact
>> > set_page_dirty() has a default reference implementation:
>>
>> Yes, Andrew had also pointed out that. And I have send v3 fix this.
>> Could you ack it?
>
> Acked-by: Wu Fengguang <fengguang.wu@intel.com>
>

Thanks.

> Thanks!
>
>> >
>> >        if (!PageDirty(page)) {
>> >                if (!TestSetPageDirty(page))
>> >                        return 1;
>>
>> return !TestSetPageDirty(page) is more simply?
>
> Yeah that's fine.
>
>> >        }
>> >        return 0;
>> >
>> > It seems the return value currently is only tested for doing
>> > balance_dirty_pages_ratelimited(). So not a big problem.
>> >
>>
>> yeah, all those are small changes no matter with any problem:-).
>
> It's always good to make it correct :) I looked at the users mainly to
> answer the question: is it a must fix for 2.6.37 or even 2.6.36.x?
>

I have no idea, I think either is okay since it's not related with any bug.

-- 
Thanks,
--Bob

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