linux-kernel - Re: [PATCH 1/2] page-allocator: Split per-cpu list into one-list-per-migrate-type

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Date:	Fri, 28 Aug 2009 21:00:25 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] page-allocator: Split per-cpu list into 
	one-list-per-migrate-type

On Fri, Aug 28, 2009 at 8:52 PM, Minchan Kim<minchan.kim@...il.com> wrote:
> Hi, Mel.
>
> On Fri, 28 Aug 2009 09:44:26 +0100
> Mel Gorman <mel@....ul.ie> wrote:
>
>> Currently the per-cpu page allocator searches the PCP list for pages of the
>> correct migrate-type to reduce the possibility of pages being inappropriate
>> placed from a fragmentation perspective. This search is potentially expensive
>> in a fast-path and undesirable. Splitting the per-cpu list into multiple
>> lists increases the size of a per-cpu structure and this was potentially
>> a major problem at the time the search was introduced. These problem has
>> been mitigated as now only the necessary number of structures is allocated
>> for the running system.
>>
>> This patch replaces a list search in the per-cpu allocator with one list per
>> migrate type. The potential snag with this approach is when bulk freeing
>> pages. We round-robin free pages based on migrate type which has little
>> bearing on the cache hotness of the page and potentially checks empty lists
>> repeatedly in the event the majority of PCP pages are of one type.
>>
>> Signed-off-by: Mel Gorman <mel@....ul.ie>
>> Acked-by: Nick Piggin <npiggin@...e.de>
>> ---
>>  include/linux/mmzone.h |    5 ++-
>>  mm/page_alloc.c        |  106 ++++++++++++++++++++++++++---------------------
>>  2 files changed, 63 insertions(+), 48 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 008cdcd..045348f 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -38,6 +38,7 @@
>>  #define MIGRATE_UNMOVABLE     0
>>  #define MIGRATE_RECLAIMABLE   1
>>  #define MIGRATE_MOVABLE       2
>> +#define MIGRATE_PCPTYPES      3 /* the number of types on the pcp lists */
>>  #define MIGRATE_RESERVE       3
>>  #define MIGRATE_ISOLATE       4 /* can't allocate from here */
>>  #define MIGRATE_TYPES         5
>> @@ -169,7 +170,9 @@ struct per_cpu_pages {
>>       int count;              /* number of pages in the list */
>>       int high;               /* high watermark, emptying needed */
>>       int batch;              /* chunk size for buddy add/remove */
>> -     struct list_head list;  /* the list of pages */
>> +
>> +     /* Lists of pages, one per migrate type stored on the pcp-lists */
>> +     struct list_head lists[MIGRATE_PCPTYPES];
>>  };
>>
>>  struct per_cpu_pageset {
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index ac3afe1..65eedb5 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -522,7 +522,7 @@ static inline int free_pages_check(struct page *page)
>>  }
>>
>>  /*
>> - * Frees a list of pages.
>> + * Frees a number of pages from the PCP lists
>>   * Assumes all pages on list are in same zone, and of same order.
>>   * count is the number of pages to free.
>>   *
>> @@ -532,23 +532,36 @@ static inline int free_pages_check(struct page *page)
>>   * And clear the zone's pages_scanned counter, to hold off the "all pages are
>>   * pinned" detection logic.
>>   */
>> -static void free_pages_bulk(struct zone *zone, int count,
>> -                                     struct list_head *list, int order)
>> +static void free_pcppages_bulk(struct zone *zone, int count,
>> +                                     struct per_cpu_pages *pcp)
>>  {
>> +     int migratetype = 0;
>> +
>
> How about caching the last sucess migratetype
> with 'per_cpu_pages->last_alloc_type'?
                                         ^^^^
                                         free
> I think it could prevent a litte spinning empty list.

Anyway, Ignore me.
I didn't see your next patch.

-- 
Kind regards,
Minchan Kim
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