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

[Minchan Kim]

2009/6/11 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>:
> Minchan Kim wrote:
>> 2009/6/11 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>:
>>> Minchan Kim ãã wrote:
>>>> On Thu, Jun 11, 2009 at 5:38 PM, KAMEZAWA
>>>> Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>>>>> How about this ?
>>>>>
>>>>> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>>>>>
>>>>> 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@xxxxxxxxxxxxxx>
>>>>> ---
>>>>> ?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.
>> Â Â Â Â /*
>> Â Â Â Â Â* When this function is being called for lumpy reclaim, we
>> Â Â Â Â Â* initially look into all LRU pages, active, inactive and
>> Â Â Â Â Â* unevictable; only give shrink_page_list evictable pages.
>> Â Â Â Â Â*/
>> Â Â Â Â if (PageUnevictable(page))
>> Â Â Â Â Â Â Â Â return ret;
>>
>> So I think we can remove this check.
>>
> agreed.
>
>>>> 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.
>>
> I'll schedule this optimization/clean up for unevictable case in queue.
> Thank you for inputs.
>
> But it's now merge-window, I'd like to push bugfix first.(1/3 and 3/3)

I agree. It's more important now.

> I'd like to scheule Unevictable case fix after rc1(when mmotm stack seems
> to be pushed out to Linus.)
> And I'll add
> int __isolate_lru_page(...)
> {
> Â Â VM_BUG_ON(PageUnevictable(page));
> }
> as sanity check for mmotm test time.
>
> Thank you for all your help.

I also thanks you for considering my comment.

You may add my review sign. :)
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>

> -Kame
>
>



-- 
Kinds regards,
Minchan Kim
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