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SubjectRe: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call
On Sun, 16 Feb 2014, Weijie Yang wrote:

> In putback_inactive_pages() and move_active_pages_to_lru(),
> lruvec is already an input parameter and pages are all from this lruvec,
> therefore there is no need to call mem_cgroup_page_lruvec() in loop.
>
> Signed-off-by: Weijie Yang <weijie.yang@samsung.com>

Looks plausible but I believe it's incorrect. The lruvec passed in
is the one we took the pages from, but there's a small but real chance
that the page has become uncharged meanwhile, and should now be put back
on the root_mem_cgroup's lruvec instead of the original memcg's lruvec.

Hugh

> ---
> mm/vmscan.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a9c74b4..4804fdb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1393,8 +1393,6 @@ putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
> continue;
> }
>
> - lruvec = mem_cgroup_page_lruvec(page, zone);
> -
> SetPageLRU(page);
> lru = page_lru(page);
> add_page_to_lru_list(page, lruvec, lru);
> @@ -1602,7 +1600,6 @@ static void move_active_pages_to_lru(struct lruvec *lruvec,
>
> while (!list_empty(list)) {
> page = lru_to_page(list);
> - lruvec = mem_cgroup_page_lruvec(page, zone);
>
> VM_BUG_ON_PAGE(PageLRU(page), page);
> SetPageLRU(page);
> --
> 1.7.10.4
>
>
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