Re: [PATCH 2/2] clean up set_page_dirty()

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 10 Nov 2010 17:00:28 +0800
Bob Liu <lliubbo@gmail.com> wrote:

> Use TestSetPageDirty() to clean up set_page_dirty().
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
>  mm/page-writeback.c |    7 ++-----
>  1 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index e8f5f06..da86224 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1268,11 +1268,8 @@ int set_page_dirty(struct page *page)
>  #endif
>  		return (*spd)(page);
>  	}
> -	if (!PageDirty(page)) {
> -		if (!TestSetPageDirty(page))
> -			return 1;
> -	}
> -	return 0;
> +
> +	return !TestSetPageDirty(page);
>  }
>  EXPORT_SYMBOL(set_page_dirty);

This just undoes the optimisation.

We could do

-		if (!TestSetPageDirty(page))
-			return 1;
+		return !TestSetPageDirty(page);

I suppose.

Or even


		return (!TestSetPageDirty(page) ^ 1);

if we're feeling stupid, and if TestSetPageDirty() reliably returns
1/0, and if that really is superior (by eliminating a test-n-branch).


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