On Wed, Nov 10, 2010 at 1:00 AM, Bob Liu <lliubbo@xxxxxxxxx> wrote:
> Use TestSetPageDirty() to clean up set_page_dirty().
>
> Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
> ---
> 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);
TestSetPageDirty compiles to a locked bts instruction (on x86). This
will acquire the cache line for exclusive access, even when the bit is
already set. I think this is why we have an extra if
(!PageDirty(page)) test - we don't want to cause cache coherency
overhead if the page is already dirty.
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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