Re: [PATCH 2/3] check unevictable flag in lumy reclaim v2

[Minchan Kim <minchan.kim@gmail.com>]

2009/6/11 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>:
> Minchan Kim さん wrote:
>> On Thu, Jun 11, 2009 at 5:38 PM, KAMEZAWA
>> Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> wrote:
>>> How about this ?
>>>
>>> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>>
>>> Lumpy reclaim check pages from their pfn. Then, it can find unevictable
>>> pages
>>> in its loop.
>>> Abort lumpy reclaim when we find Unevictable page, we never get a lump
>>> of pages for requested order.
>>>
>>> Changelog: v1->v2
>>> ?- rewrote commet.
>>>
>>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>> ---
>>> ?mm/vmscan.c | ? ?9 +++++++++
>>> ?1 file changed, 9 insertions(+)
>>>
>>> Index: lumpy-reclaim-trial/mm/vmscan.c
>>> ===================================================================
>>> --- lumpy-reclaim-trial.orig/mm/vmscan.c
>>> +++ lumpy-reclaim-trial/mm/vmscan.c
>>> @@ -936,6 +936,15 @@ static unsigned long isolate_lru_pages(u
>>> ? ? ? ? ? ? ? ? ? ? ? ?/* Check that we have not crossed a zone
>>> boundary. */
>>> ? ? ? ? ? ? ? ? ? ? ? ?if (unlikely(page_zone_id(cursor_page) !=
>>> zone_id))
>>> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?continue;
>>> + ? ? ? ? ? ? ? ? ? ? ? /*
>>> + ? ? ? ? ? ? ? ? ? ? ? ?* We tries to free all pages in this range to
>>> create
>>> + ? ? ? ? ? ? ? ? ? ? ? ?* a free large page. Then, if the range
>>> includes a page
>>> + ? ? ? ? ? ? ? ? ? ? ? ?* never be reclaimed, we have no reason to do
>>> more.
>>> + ? ? ? ? ? ? ? ? ? ? ? ?* PageUnevictable page is not a page which can
>>> be
>>> + ? ? ? ? ? ? ? ? ? ? ? ?* easily freed. Abort this scan now.
>>> + ? ? ? ? ? ? ? ? ? ? ? ?*/
>>> + ? ? ? ? ? ? ? ? ? ? ? if (unlikely(PageUnevictable(cursor_page)))
>>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? break;
>>
>> __isolate_lru_pages already checked PageUnevictable to return error.
>> I want to remove repeated check although it is trivial.
>>
>> By your patch, It seems to remove PageUnevictable check in
>> __isolate_lru_pages.
>>
> yes.
>
>> But I know that. If we remove PageUnevictable check in
>> __isolate_lru_pages, it can't go into BUG in non-lumpy case. ( I
>> mentioned following as code)
>>
> In non-lumpy case, we'll never see Unevictable, maybe.

I think so if it doesn't happen RAM failure.
AFAIK, Unevictable check didn't related with RAM failure.

>
>>                 case -EBUSY:
>>                         /* else it is being freed elsewhere */
>>                         list_move(&page->lru, src);
>>                         continue;
>>
>>                 default:
>>                         BUG();
>>                 }
>>
>>
>> It means we can remove BUG in non-lumpy case and then add BUG into
>> __isolate_lru_pages directly.
>>
>> If we can do it, we can remove unnecessary PageUnevictable check in
>> __isolate_lru_page.
>>
> Hmm, but Unevicable check had tons of troubles at its implementation
> and I don't want to do it at once.

I think it's not a big problem.
As comment said, the check's goal is to prevent in lumpy case.
        /*
         * When this function is being called for lumpy reclaim, we
         * initially look into all LRU pages, active, inactive and
         * unevictable; only give shrink_page_list evictable pages.
         */
        if (PageUnevictable(page))
                return ret;

So I think we can remove this check.

>> I am not sure this is right in case of memcg.
>>
> I think we don't see Unevictable in memcg's path if my memcg-lru code
> works as designed.
>
> I'll postpone this patch for a while until my brain works well.

If you have a concern about that, how about this ?
(This code will be hunk since gmail webserver always mangle. Pz,forgive me)
Also, we can CC original authors.

--- a/mm/vmscan.c
++ b/mm/vmscan.c
@@ -936,19 +936,20 @@ static unsigned long isolate_lru_pages(unsigned
long nr_to_scan,
                        /* Check that we have not crossed a zone boundary. */
                        if (unlikely(page_zone_id(cursor_page) != zone_id))
                                continue;
-                       switch (__isolate_lru_page(cursor_page, mode, file)) {
-                       case 0:
+                       if (__isolate_lru_page(cursor_page, mode, file) == 0) {
                                list_move(&cursor_page->lru, dst);
                                nr_taken++;
                                scan++;
-                               break;
-
-                       case -EBUSY:
-                               /* else it is being freed elsewhere */
-                               list_move(&cursor_page->lru, src);
-                       default:
-                               break;  /* ! on LRU or wrong list */
                        }
+                       else if (PageUnevictable(cursor_page))
+                                       /*
+                                * We tries to free all pages in this
range to create
+                                * a free large page. Then, if the
range includes a page
+                                * never be reclaimed, we have no
reason to do more.
+                                * PageUnevictable page is not a page
which can be
+                                * easily freed. Abort this scan now.
+                                */
+                               break
                }
        }


> Thanks,
> -Kame
>
>



-- 
Kinds regards,
Minchan Kim

--
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>