Re: [PATCH v2 3/7] memcg: use compound_order rather than hpage_nr_pages

[Punit Agrawal]

Punit Agrawal <punit.agrawal@xxxxxxx> writes:

> Tsukada-san,
>
> I am not familiar with memcg so can't comment about whether the patchset
> is the right way to solve the problem outlined in the cover letter but
> had a couple of comments about this patch.
>
> TSUKADA Koutaro <tsukada@xxxxxxxxxxxx> writes:
>
>> The current memcg implementation assumes that the compound page is THP.
>> In order to be able to charge surplus hugepage, we use compound_order.
>>
>> Signed-off-by: TSUKADA Koutaro <tsukada@xxxxxxxxxxxx>
>
> Please move this before Patch 1/7. This is to prevent wrong accounting
> of pages to memcg for size != PMD_SIZE.

I just noticed that the default state is off so the change isn't enabled
until the sysfs node is exposed in the next patch. Please ignore this
comment.

One below still applies.

>
>> ---
>>  memcontrol.c |   10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 2bd3df3..a8f1ff8 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -4483,7 +4483,7 @@ static int mem_cgroup_move_account(struct page *page,
>>  				   struct mem_cgroup *to)
>>  {
>>  	unsigned long flags;
>> -	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>> +	unsigned int nr_pages = compound ? (1 << compound_order(page)) : 1;
>
> Instead of replacing calls to hpage_nr_pages(), is it possible to modify
> it to do the calculation?
>
> Thanks,
> Punit
>
>>  	int ret;
>>  	bool anon;
>>
>> @@ -5417,7 +5417,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
>>  			  bool compound)
>>  {
>>  	struct mem_cgroup *memcg = NULL;
>> -	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>> +	unsigned int nr_pages = compound ? (1 << compound_order(page)) : 1;
>>  	int ret = 0;
>>
>>  	if (mem_cgroup_disabled())
>> @@ -5478,7 +5478,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
>>  void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
>>  			      bool lrucare, bool compound)
>>  {
>> -	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>> +	unsigned int nr_pages = compound ? (1 << compound_order(page)) : 1;
>>
>>  	VM_BUG_ON_PAGE(!page->mapping, page);
>>  	VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);
>> @@ -5522,7 +5522,7 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
>>  void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg,
>>  		bool compound)
>>  {
>> -	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>> +	unsigned int nr_pages = compound ? (1 << compound_order(page)) : 1;
>>
>>  	if (mem_cgroup_disabled())
>>  		return;
>> @@ -5729,7 +5729,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
>>
>>  	/* Force-charge the new page. The old one will be freed soon */
>>  	compound = PageTransHuge(newpage);
>> -	nr_pages = compound ? hpage_nr_pages(newpage) : 1;
>> +	nr_pages = compound ? (1 << compound_order(newpage)) : 1;
>>
>>  	page_counter_charge(&memcg->memory, nr_pages);
>>  	if (do_memsw_account())