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

Joonsoo Kim
2016-06-03T12:48:01Z

2016-06-03 19:23 GMT+09:00 Vlastimil Babka <vbabka@suse.cz>:
> On 05/26/2016 04:37 AM, js1304@gmail.com wrote:
>>
>> From: Joonsoo Kim <iamjoonsoo.kim@lge.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@lge.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.