[PATCH] mm: __rmqueue_fallback() should respect pageblock type

[PATCH] mm: __rmqueue_fallback() should respect pageblock type

[kosaki.motohiro]

From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

When __rmqueue_fallback() don't find out a free block with the same size
of required, it splits a larger page and puts back rest peiece of the page
to free list.

But it has one serious mistake. When putting back, __rmqueue_fallback()
always use start_migratetype if type is not CMA. However, __rmqueue_fallback()
is only called when all of start_migratetype queue are empty. That said,
__rmqueue_fallback always put back memory to wrong queue except
try_to_steal_freepages() changed pageblock type (i.e. requested size is
smaller than half of page block). Finally, antifragmentation framework
increase fragmenation instead of decrease.

Mel's original anti fragmentation do the right thing. But commit 47118af076
(mm: mmzone: MIGRATE_CMA migration type added) broke it.

This patch restores sane and old behavior.

Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 mm/page_alloc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dd886fa..ea7bb9a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1101,7 +1101,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
 			 */
 			expand(zone, page, order, current_order, area,
 			       is_migrate_cma(migratetype)
-			     ? migratetype : start_migratetype);
+			     ? migratetype : new_type);
 
 			trace_mm_page_alloc_extfrag(page, order,
 				current_order, start_migratetype, migratetype,
-- 
1.7.1

Re: [PATCH] mm: __rmqueue_fallback() should respect pageblock type

[Andrew Morton]

On Thu, 31 Oct 2013 00:24:49 -0400 kosaki.motohiro@gmail.com wrote:

> When __rmqueue_fallback() don't find out a free block with the same size
> of required, it splits a larger page and puts back rest peiece of the page
> to free list.
> 
> But it has one serious mistake. When putting back, __rmqueue_fallback()
> always use start_migratetype if type is not CMA. However, __rmqueue_fallback()
> is only called when all of start_migratetype queue are empty. That said,
> __rmqueue_fallback always put back memory to wrong queue except
> try_to_steal_freepages() changed pageblock type (i.e. requested size is
> smaller than half of page block). Finally, antifragmentation framework
> increase fragmenation instead of decrease.
> 
> Mel's original anti fragmentation do the right thing. But commit 47118af076
> (mm: mmzone: MIGRATE_CMA migration type added) broke it.
> 
> This patch restores sane and old behavior.

What are the user-visible runtime effects of this change?

Re: [PATCH] mm: __rmqueue_fallback() should respect pageblock type

[KOSAKI Motohiro]

(10/31/13 12:35 AM), Andrew Morton wrote:
> On Thu, 31 Oct 2013 00:24:49 -0400 kosaki.motohiro@gmail.com wrote:
>
>> When __rmqueue_fallback() don't find out a free block with the same size
>> of required, it splits a larger page and puts back rest peiece of the page
>> to free list.
>>
>> But it has one serious mistake. When putting back, __rmqueue_fallback()
>> always use start_migratetype if type is not CMA. However, __rmqueue_fallback()
>> is only called when all of start_migratetype queue are empty. That said,
>> __rmqueue_fallback always put back memory to wrong queue except
>> try_to_steal_freepages() changed pageblock type (i.e. requested size is
>> smaller than half of page block). Finally, antifragmentation framework
>> increase fragmenation instead of decrease.
>>
>> Mel's original anti fragmentation do the right thing. But commit 47118af076
>> (mm: mmzone: MIGRATE_CMA migration type added) broke it.
>>
>> This patch restores sane and old behavior.
>
> What are the user-visible runtime effects of this change?

Memory fragmentation may increase compaction rate. (And then system get unnecessary
slow down)

Re: [PATCH] mm: __rmqueue_fallback() should respect pageblock type

[KOSAKI Motohiro]

(10/31/13 12:24 AM), kosaki.motohiro@gmail.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> When __rmqueue_fallback() don't find out a free block with the same size
> of required, it splits a larger page and puts back rest peiece of the page
> to free list.
> 
> But it has one serious mistake. When putting back, __rmqueue_fallback()
> always use start_migratetype if type is not CMA. However, __rmqueue_fallback()
> is only called when all of start_migratetype queue are empty. That said,
> __rmqueue_fallback always put back memory to wrong queue except
> try_to_steal_freepages() changed pageblock type (i.e. requested size is
> smaller than half of page block). Finally, antifragmentation framework
> increase fragmenation instead of decrease.
> 
> Mel's original anti fragmentation do the right thing. But commit 47118af076
> (mm: mmzone: MIGRATE_CMA migration type added) broke it.
> 
> This patch restores sane and old behavior.
> 
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> ---
>   mm/page_alloc.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dd886fa..ea7bb9a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1101,7 +1101,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
>   			 */
>   			expand(zone, page, order, current_order, area,
>   			       is_migrate_cma(migratetype)
> -			     ? migratetype : start_migratetype);
> +			     ? migratetype : new_type);

Oops, this can be simplified to following because try_to_steal_freepages() has cma check.


-                       expand(zone, page, order, current_order, area,
-                              is_migrate_cma(migratetype)
-                            ? migratetype : start_migratetype);
+                       expand(zone, page, order, current_order, area, new_type);