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

Punit Agrawal
2018-05-18T17:46:49Z

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@ascade.co.jp> 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@ascade.co.jp>

Please move this before Patch 1/7. This is to prevent wrong accounting
of pages to memcg for size != PMD_SIZE.

> ---
> 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())