linux-kernel - Re: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page

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Message-ID: <CAL1ERfO4yYMRBO8XEM0oCwBb6NOqZRVGq648ncerM9XuyPPJkw@mail.gmail.com>
Date:	Sun, 16 Feb 2014 13:01:55 +0800
From:	Weijie Yang <weijie.yang.kh@...il.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Weijie Yang <weijie.yang@...sung.com>, riel@...hat.com,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec()
 call

On Sun, Feb 16, 2014 at 12:00 PM, Hugh Dickins <hughd@...gle.com> wrote:
> 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@...sung.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.

Hi Hugh,

Thanks for your review.
Frankly speaking, I am not very sure about it, that is why I add a RFC tag here.
So,  do we need update the reclaim_stat meanwhile as we change the lruvec?

Regards,

> 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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