Re: [PATCH] vmscan: reclaim_clean_pages_from_list() must count mlocked pages

[Jaewon Kim]

On 2015ë 08ì 04ì 00:33, Minchan Kim wrote:
> On Mon, Aug 03, 2015 at 11:55:46PM +0900, Jaewon Kim wrote:
>>
>>
>> On 2015ë 08ì 03ì 21:27, Minchan Kim wrote:
>>> Hello,
>>>
>>> On Mon, Aug 03, 2015 at 07:18:27PM +0900, Jaewon Kim wrote:
>>>> reclaim_clean_pages_from_list() decreases NR_ISOLATED_FILE by returned
>>>> value from shrink_page_list(). But mlocked pages in the isolated
>>>> clean_pages page list would be removed from the list but not counted as
>>>> nr_reclaimed. Fix this miscounting by returning the number of mlocked
>>>> pages and count it.
>>>
>>> If there are pages not able to reclaim, VM try to migrate it and
>>> have to handle the stat in migrate_pages.
>>> If migrate_pages fails again, putback-fiends should handle it.
>>>
>>> Is there anyting I am missing now?
>>>
>>> Thanks.
>>>
>> Hello
>>
>> Only pages in cc->migratepages will be handled by migrate_pages or
>> putback_movable_pages, and NR_ISOLATED_FILE will be counted properly.
>> However mlocked pages will not be put back into cc->migratepages,
>> and also not be counted in NR_ISOLATED_FILE because putback_lru_page
>> in shrink_page_list does not increase NR_ISOLATED_FILE.
>> The current reclaim_clean_pages_from_list assumes that shrink_page_list
>> returns number of pages removed from the candidate list.
>>
>> i.e)
>> isolate_migratepages_range    : NR_ISOLATED_FILE += 10
>> reclaim_clean_pages_from_list : NR_ISOLATED_FILE -= 5 (1 mlocked page)
>> migrate_pages                 : NR_ISOLATED_FILE -=4
>> => NR_ISOLATED_FILE increased by 1
> 
> Thanks for the clarity.
> 
> I think the problem is shrink_page_list is awkard. It put back to
> unevictable pages instantly instead of passing it to caller while
> it relies on caller for non-reclaimed-non-unevictable page's putback.
> 
> I think we can make it consistent so that shrink_page_list could
> return non-reclaimed pages via page_list and caller can handle it.
> As a bonus, it could try to migrate mlocked pages without retrial.
> 
>>
>> Thank you.

To make clear do you mean changing shrink_page_list like this rather than
previous my suggestion?

@@ -1157,7 +1157,7 @@ cull_mlocked:
                if (PageSwapCache(page))
                        try_to_free_swap(page);
                unlock_page(page);
-               putback_lru_page(page);
+               list_add(&page->lru, &ret_pages);
                continue;

Thank you.


>>>>
>>>> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>>>> ---
>>>>  mm/vmscan.c | 10 ++++++++--
>>>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>>> index 5e8eadd..5837695 100644
>>>> --- a/mm/vmscan.c
>>>> +++ b/mm/vmscan.c
>>>> @@ -849,6 +849,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>>>>  				      unsigned long *ret_nr_congested,
>>>>  				      unsigned long *ret_nr_writeback,
>>>>  				      unsigned long *ret_nr_immediate,
>>>> +				      unsigned long *ret_nr_mlocked,
>>>>  				      bool force_reclaim)
>>>>  {
>>>>  	LIST_HEAD(ret_pages);
>>>> @@ -1158,6 +1159,7 @@ cull_mlocked:
>>>>  			try_to_free_swap(page);
>>>>  		unlock_page(page);
>>>>  		putback_lru_page(page);
>>>> +		(*ret_nr_mlocked)++;
>>>>  		continue;
>>>>  
>>>>  activate_locked:
>>>> @@ -1197,6 +1199,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>>>>  		.may_unmap = 1,
>>>>  	};
>>>>  	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
>>>> +	unsigned long nr_mlocked = 0;
>>>>  	struct page *page, *next;
>>>>  	LIST_HEAD(clean_pages);
>>>>  
>>>> @@ -1210,8 +1213,10 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>>>>  
>>>>  	ret = shrink_page_list(&clean_pages, zone, &sc,
>>>>  			TTU_UNMAP|TTU_IGNORE_ACCESS,
>>>> -			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
>>>> +			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5,
>>>> +			&nr_mlocked, true);
>>>>  	list_splice(&clean_pages, page_list);
>>>> +	ret += nr_mlocked;
>>>>  	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
>>>>  	return ret;
>>>>  }
>>>> @@ -1523,6 +1528,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>>>>  	unsigned long nr_unqueued_dirty = 0;
>>>>  	unsigned long nr_writeback = 0;
>>>>  	unsigned long nr_immediate = 0;
>>>> +	unsigned long nr_mlocked = 0;
>>>>  	isolate_mode_t isolate_mode = 0;
>>>>  	int file = is_file_lru(lru);
>>>>  	struct zone *zone = lruvec_zone(lruvec);
>>>> @@ -1565,7 +1571,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>>>>  
>>>>  	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
>>>>  				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
>>>> -				&nr_writeback, &nr_immediate,
>>>> +				&nr_writeback, &nr_immediate, &nr_mlocked,
>>>>  				false);
>>>>  
>>>>  	spin_lock_irq(&zone->lru_lock);
>>>> -- 
>>>> 1.9.1
>>>>
>>>
> 
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