Re: [RFC 8/8] compaction: make compaction use in-order putback

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

On Wed, Apr 27, 2011 at 5:39 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Wed, 27 Apr 2011 01:25:25 +0900
> Minchan Kim <minchan.kim@gmail.com> wrote:
>
>> Compaction is good solution to get contiguos page but it makes
>> LRU churing which is not good.
>> This patch makes that compaction code use in-order putback so
>> after compaction completion, migrated pages are keeping LRU ordering.
>>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> Cc: Mel Gorman <mgorman@suse.de>
>> Cc: Rik van Riel <riel@redhat.com>
>> Cc: Andrea Arcangeli <aarcange@redhat.com>
>> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
>> ---
>>  mm/compaction.c |   22 +++++++++++++++-------
>>  1 files changed, 15 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index a2f6e96..480d2ac 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -211,11 +211,11 @@ static void isolate_freepages(struct zone *zone,
>>  /* Update the number of anon and file isolated pages in the zone */
>>  static void acct_isolated(struct zone *zone, struct compact_control *cc)
>>  {
>> -     struct page *page;
>> +     struct pages_lru *pages_lru;
>>       unsigned int count[NR_LRU_LISTS] = { 0, };
>>
>> -     list_for_each_entry(page, &cc->migratepages, lru) {
>> -             int lru = page_lru_base_type(page);
>> +     list_for_each_entry(pages_lru, &cc->migratepages, lru) {
>> +             int lru = page_lru_base_type(pages_lru->page);
>>               count[lru]++;
>>       }
>>
>> @@ -281,6 +281,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>>       spin_lock_irq(&zone->lru_lock);
>>       for (; low_pfn < end_pfn; low_pfn++) {
>>               struct page *page;
>> +             struct pages_lru *pages_lru;
>>               bool locked = true;
>>
>>               /* give a chance to irqs before checking need_resched() */
>> @@ -334,10 +335,16 @@ static unsigned long isolate_migratepages(struct zone *zone,
>>                       continue;
>>               }
>>
>> +             pages_lru = kmalloc(sizeof(struct pages_lru), GFP_ATOMIC);
>> +             if (pages_lru)
>> +                     continue;
>
> Hmm, can't we use fixed size of statically allocated pages_lru, per-node or
> per-zone ? I think using kmalloc() in memory reclaim path is risky.

Yes. we can enhance it with pagevec-like approach.
It's my TODO list.  :)

In compaction POV, it is used by reclaiming big order pages so most of
time order-0 pages are enough. It's basic assumption of compaction so
it shouldn't be a problem.

Thanks for the review, Kame.


-- 
Kind regards,
Minchan Kim

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