linux-kernel - Re: [PATCH v2 2/7] mm/page_owner: initialize page owner without holding the zone lock

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Date:	Fri, 3 Jun 2016 21:47:52 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Minchan Kim <minchan@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Michal Hocko <mhocko@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 2/7] mm/page_owner: initialize page owner without
 holding the zone lock

2016-06-03 19:23 GMT+09:00 Vlastimil Babka <vbabka@...e.cz>:
> On 05/26/2016 04:37 AM, js1304@...il.com wrote:
>>
>> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>>
>> It's not necessary to initialized page_owner with holding the zone lock.
>> It would cause more contention on the zone lock although it's not
>> a big problem since it is just debug feature. But, it is better
>> than before so do it. This is also preparation step to use stackdepot
>> in page owner feature. Stackdepot allocates new pages when there is no
>> reserved space and holding the zone lock in this case will cause deadlock.
>>
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>> ---
>>  mm/compaction.c     | 3 +++
>>  mm/page_alloc.c     | 2 --
>>  mm/page_isolation.c | 9 ++++++---
>>  3 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 8e013eb..6043ef8 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -20,6 +20,7 @@
>>  #include <linux/kasan.h>
>>  #include <linux/kthread.h>
>>  #include <linux/freezer.h>
>> +#include <linux/page_owner.h>
>>  #include "internal.h"
>>
>>  #ifdef CONFIG_COMPACTION
>> @@ -80,6 +81,8 @@ static void map_pages(struct list_head *list)
>>                 arch_alloc_page(page, order);
>>                 kernel_map_pages(page, nr_pages, 1);
>>                 kasan_alloc_pages(page, order);
>> +
>> +               set_page_owner(page, order, __GFP_MOVABLE);
>>                 if (order)
>>                         split_page(page, order);
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 5134f46..1b1ca57 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2507,8 +2507,6 @@ int __isolate_free_page(struct page *page, unsigned
>> int order)
>>         zone->free_area[order].nr_free--;
>>         rmv_page_order(page);
>>
>> -       set_page_owner(page, order, __GFP_MOVABLE);
>> -
>>         /* Set the pageblock if the isolated page is at least a pageblock
>> */
>>         if (order >= pageblock_order - 1) {
>>                 struct page *endpage = page + (1 << order) - 1;
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 612122b..927f5ee 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -7,6 +7,7 @@
>>  #include <linux/pageblock-flags.h>
>>  #include <linux/memory.h>
>>  #include <linux/hugetlb.h>
>> +#include <linux/page_owner.h>
>>  #include "internal.h"
>>
>>  #define CREATE_TRACE_POINTS
>> @@ -108,8 +109,6 @@ static void unset_migratetype_isolate(struct page
>> *page, unsigned migratetype)
>>                         if (pfn_valid_within(page_to_pfn(buddy)) &&
>>                             !is_migrate_isolate_page(buddy)) {
>>                                 __isolate_free_page(page, order);
>> -                               kernel_map_pages(page, (1 << order), 1);
>> -                               set_page_refcounted(page);
>>                                 isolated_page = page;
>>                         }
>>                 }
>> @@ -128,8 +127,12 @@ static void unset_migratetype_isolate(struct page
>> *page, unsigned migratetype)
>>         zone->nr_isolate_pageblock--;
>>  out:
>>         spin_unlock_irqrestore(&zone->lock, flags);
>> -       if (isolated_page)
>> +       if (isolated_page) {
>> +               kernel_map_pages(page, (1 << order), 1);
>
>
> So why we don't need the other stuff done by e.g. map_pages()? For example
> arch_alloc_page() and kasan_alloc_pages(). Maybe kasan_free_pages() (called
> below via __free_pages() I assume) now doesn't check if the allocation part
> was done. But maybe it will start doing that?
>
> See how the multiple places doing similar stuff is fragile? :(

I answered it in reply of comment of patch 1.

>> +               set_page_refcounted(page);
>> +               set_page_owner(page, order, __GFP_MOVABLE);
>>                 __free_pages(isolated_page, order);
>
>
> This mixing of "isolated_page" and "page" is not a bug, but quite ugly.
> Can't isolated_page variable just be a bool?
>

Looks better. I will do it.

Thanks.