Hi,
On Wed, Mar 24, 2010 at 08:11:27PM +0800, Bob Liu wrote:
> In funtion shrink_page_list(), page_mapped() is called several
> times,save it to local val to reduce atomic_read.
>
> Signed-off-by: Bob Liu <lliubbo@xxxxxxxxx>
> ---
> mm/vmscan.c | 8 +++++---
> 1 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 79c8098..08cc3ac 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -637,6 +637,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> struct address_space *mapping;
> struct page *page;
> int may_enter_fs;
> + int page_mapcount;
>
> cond_resched();
>
> @@ -653,11 +654,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> if (unlikely(!page_evictable(page, NULL)))
> goto cull_mlocked;
>
> - if (!sc->may_unmap && page_mapped(page))
> + page_mapcount = page_mapped(page);
> + if (!sc->may_unmap && page_mapcount)
> goto keep_locked;
>
> /* Double the slab pressure for mapped and swapcache pages */
> - if (page_mapped(page) || PageSwapCache(page))
> + if (page_mapcount || PageSwapCache(page))
> sc->nr_scanned++;
Note that the mapcount is unstable and might very well drop while this code
runs.
The first two instances are close enough together that a change is unlikely,
but between them and the below check before try_to_unmap() we might be even
waiting for writeback to complete.
try_to_unmap() will figure it out, but it would lock the mapping first and
then read the mapcount.
I am unsure whether the change is worth it.
> may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> @@ -707,7 +709,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> * The page is mapped into the page tables of one or more
> * processes. Try to unmap it here.
> */
> - if (page_mapped(page) && mapping) {
> + if (page_mapcount && mapping) {
> switch (try_to_unmap(page, TTU_UNMAP)) {
> case SWAP_FAIL:
> goto activate_locked;
--
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