Re: [RFC 2/8] compaction: make isolate_lru_page with filter aware

[Minchan Kim]

Hi Hannes,

On Thu, Apr 28, 2011 at 5:48 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> On Wed, Apr 27, 2011 at 01:25:19AM +0900, Minchan Kim wrote:
>> In async mode, compaction doesn't migrate dirty or writeback pages.
>> So, it's meaningless to pick the page and re-add it to lru list.
>>
>> Of course, when we isolate the page in compaction, the page might
>> be dirty or writeback but when we try to migrate the page, the page
>> would be not dirty, writeback. So it could be migrated. But it's
>> very unlikely as isolate and migration cycle is much faster than
>> writeout.
>>
>> So, this patch helps cpu and prevent unnecessary LRU churning.
>>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>> Cc: Mel Gorman <mgorman@xxxxxxx>
>> Cc: Rik van Riel <riel@xxxxxxxxxx>
>> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
>> ---
>> Âmm/compaction.c | Â Â2 +-
>> Â1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index dea32e3..9f80b5a 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -335,7 +335,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>> Â Â Â Â Â Â Â }
>>
>> Â Â Â Â Â Â Â /* Try isolate the page */
>> - Â Â Â Â Â Â if (__isolate_lru_page(page, ISOLATE_BOTH, 0, 0, 0) != 0)
>> + Â Â Â Â Â Â if (__isolate_lru_page(page, ISOLATE_BOTH, 0, !cc->sync, 0) != 0)
>> Â Â Â Â Â Â Â Â Â Â Â continue;
>
> With the suggested flags argument from 1/8, this would look like:
>
> Â Â Â Âflags = ISOLATE_BOTH;
> Â Â Â Âif (!cc->sync)
> Â Â Â Â Â Â Â Âflags |= ISOLATE_CLEAN;
>
> ?

Yes. I will change it.

>
> Anyway, nice change indeed!

Thanks!


-- 
Kind regards,
Minchan Kim
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