* [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call
@ 2014-02-16 3:30 Weijie Yang
2014-02-16 4:00 ` Hugh Dickins
0 siblings, 1 reply; 4+ messages in thread
From: Weijie Yang @ 2014-02-16 3:30 UTC (permalink / raw)
To: riel
Cc: 'Mel Gorman', 'Andrew Morton',
'Minchan Kim', weijie.yang.kh, 'linux-kernel',
'Linux-MM'
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>
---
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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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call
2014-02-16 3:30 [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call Weijie Yang
@ 2014-02-16 4:00 ` Hugh Dickins
2014-02-16 5:01 ` Weijie Yang
0 siblings, 1 reply; 4+ messages in thread
From: Hugh Dickins @ 2014-02-16 4:00 UTC (permalink / raw)
To: Weijie Yang
Cc: riel, Mel Gorman, Andrew Morton, Minchan Kim, weijie.yang.kh,
linux-kernel, Linux-MM
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
>
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
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>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call
2014-02-16 4:00 ` Hugh Dickins
@ 2014-02-16 5:01 ` Weijie Yang
2014-02-16 5:25 ` Hugh Dickins
0 siblings, 1 reply; 4+ messages in thread
From: Weijie Yang @ 2014-02-16 5:01 UTC (permalink / raw)
To: Hugh Dickins
Cc: Weijie Yang, riel, Mel Gorman, Andrew Morton, Minchan Kim,
linux-kernel, Linux-MM
On Sun, Feb 16, 2014 at 12:00 PM, Hugh Dickins <hughd@google.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@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.
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
>>
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org. For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call
2014-02-16 5:01 ` Weijie Yang
@ 2014-02-16 5:25 ` Hugh Dickins
0 siblings, 0 replies; 4+ messages in thread
From: Hugh Dickins @ 2014-02-16 5:25 UTC (permalink / raw)
To: Weijie Yang
Cc: Hugh Dickins, Weijie Yang, riel, Mel Gorman, Andrew Morton,
Minchan Kim, linux-kernel, Linux-MM
On Sun, 16 Feb 2014, Weijie Yang wrote:
> On Sun, Feb 16, 2014 at 12:00 PM, Hugh Dickins <hughd@google.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@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.
>
> 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?
No, it's not worth bothering about, it's only for stats and this is an
unlikely case; whereas wrong memcg can be a significant correctness issue.
Hugh
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2014-02-16 3:30 [RFC PATCH] mm/vmscan: remove two un-needed mem_cgroup_page_lruvec() call Weijie Yang
2014-02-16 4:00 ` Hugh Dickins
2014-02-16 5:01 ` Weijie Yang
2014-02-16 5:25 ` Hugh Dickins
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