linux-kernel - Re: [RFC PATCH 2/6] mm: memcg: make memcg huge page split support any order split.

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Message-ID: <6F7C40E6-26DA-4190-A077-D70412927A97@nvidia.com>
Date:   Fri, 13 Nov 2020 19:56:50 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Roman Gushchin <guro@...com>
CC:     <linux-mm@...ck.org>, Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        Yang Shi <shy828301@...il.com>,
        "Michal Hocko" <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        "Ralph Campbell" <rcampbell@...dia.com>,
        David Nellans <dnellans@...dia.com>
Subject: Re: [RFC PATCH 2/6] mm: memcg: make memcg huge page split support any
 order split.

On 13 Nov 2020, at 19:23, Roman Gushchin wrote:

> On Wed, Nov 11, 2020 at 03:40:04PM -0500, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> It reads thp_nr_pages and splits to provided new_nr. It prepares for
>> upcoming changes to support split huge page to any lower order.
>>
>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>>  include/linux/memcontrol.h | 5 +++--
>>  mm/huge_memory.c           | 2 +-
>>  mm/memcontrol.c            | 4 ++--
>>  3 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 0f4dd7829fb2..b3bac79ceed6 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -1105,7 +1105,7 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>>  }
>>
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -void mem_cgroup_split_huge_fixup(struct page *head);
>> +void mem_cgroup_split_huge_fixup(struct page *head, unsigned int new_nr);
>>  #endif
>>
>>  #else /* CONFIG_MEMCG */
>> @@ -1451,7 +1451,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>>  	return 0;
>>  }
>>
>> -static inline void mem_cgroup_split_huge_fixup(struct page *head)
>> +static inline void mem_cgroup_split_huge_fixup(struct page *head,
>> +					       unsigned int new_nr)
>>  {
>>  }
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index c4fead5ead31..f599f5b9bf7f 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2429,7 +2429,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>>  	lruvec = mem_cgroup_page_lruvec(head, pgdat);
>>
>>  	/* complete memcg works before add pages to LRU */
>> -	mem_cgroup_split_huge_fixup(head);
>> +	mem_cgroup_split_huge_fixup(head, 1);
>>
>>  	if (PageAnon(head) && PageSwapCache(head)) {
>>  		swp_entry_t entry = { .val = page_private(head) };
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 33f632689cee..e9705ba6bbcc 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -3247,7 +3247,7 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size)
>>   * Because tail pages are not marked as "used", set it. We're under
>>   * pgdat->lru_lock and migration entries setup in all page mappings.
>>   */
>> -void mem_cgroup_split_huge_fixup(struct page *head)
>> +void mem_cgroup_split_huge_fixup(struct page *head, unsigned int new_nr)
>
> I'd go with unsigned int new_order, then it's obvious that we can split
> the original page without any leftovers.

Makes sense. Will change it.

>
> Other than that the patch looks good!
> Acked-by: Roman Gushchin <guro@...com>

Thanks.

>>  {
>>  	struct mem_cgroup *memcg = page_memcg(head);
>>  	int i;
>> @@ -3255,7 +3255,7 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>>  	if (mem_cgroup_disabled())
>>  		return;
>>
>> -	for (i = 1; i < thp_nr_pages(head); i++) {
>> +	for (i = new_nr; i < thp_nr_pages(head); i += new_nr) {
>>  		css_get(&memcg->css);
>>  		head[i].memcg_data = (unsigned long)memcg;
>>  	}
>> -- 
>> 2.28.0
>>


—
Best Regards,
Yan Zi

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