linux-kernel - Re: [PATCH v2 3/7] memcg: use compound_order rather than hpage_nr

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Message-ID: <87wow0zwja.fsf@e105922-lin.cambridge.arm.com>
Date:   Fri, 18 May 2018 18:46:49 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     TSUKADA Koutaro <tsukada@...ade.co.jp>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jonathan Corbet <corbet@....net>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        David Rientjes <rientjes@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Marc-Andre Lureau <marcandre.lureau@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v2 3/7] memcg: use compound_order rather than hpage_nr_pages

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@...ade.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@...ade.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())