From: Johannes Weiner <hannes@cmpxchg.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Roman Gushchin <guro@fb.com>,
Andrew Morton <akpm@linux-foundation.org>,
Shakeel Butt <shakeelb@google.com>,
Michal Hocko <mhocko@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kernel-team@fb.com
Subject: Re: [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag
Date: Thu, 1 Oct 2020 13:27:13 -0400 [thread overview]
Message-ID: <20201001172713.GA500308@cmpxchg.org> (raw)
In-Reply-To: <20201001170036.GA29848@blackbook>
On Thu, Oct 01, 2020 at 07:00:36PM +0200, Michal Koutný wrote:
> Hi.
>
> On Wed, Sep 30, 2020 at 05:27:10PM -0700, Roman Gushchin <guro@fb.com> wrote:
> > @@ -369,8 +371,12 @@ enum page_memcg_data_flags {
> > */
> > static inline struct mem_cgroup *page_memcg(struct page *page)
> > {
> > + unsigned long memcg_data = page->memcg_data;
> > +
> > VM_BUG_ON_PAGE(PageSlab(page), page);
> > - return (struct mem_cgroup *)page->memcg_data;
> > + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page);
> > +
> > + return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
> > }
> Shouldn't this change go also into page_memcg_rcu()? (I don't think the
> current single user (workingset_activation() would pass a non-slab
> kernel page but for consistency sake.)
+1
> Alternatively, I'm thinking why (in its single use) is there
> page_memcg_rcu() a separate function to page_memcg() (cross memcg page
> migration?).
It goes back to commit 55779ec759ccc3c12b917b3712a7716e1140c652.
The activation code is the only path where page migration is not
excluded. Because unlike with page state statistics, we don't really
mind a race when counting an activation event.
I do think there is a bug, though: mem_cgroup_move_account() should
use WRITE_ONCE() on page->mem_cgroup.
next prev parent reply other threads:[~2020-10-01 17:28 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 0:27 [PATCH v4 0/4] mm: allow mapping accounted kernel pages to userspace Roman Gushchin
2020-10-01 0:27 ` [PATCH v4 1/4] mm: memcontrol: use helpers to access page's memcg data Roman Gushchin
2020-10-01 13:46 ` Johannes Weiner
2020-10-01 18:27 ` Roman Gushchin
2020-10-01 18:59 ` Johannes Weiner
2020-10-01 20:51 ` Roman Gushchin
2020-10-02 14:22 ` Johannes Weiner
2020-10-01 0:27 ` [PATCH v4 2/4] mm: memcontrol/slab: use helpers to access slab page's memcg_data Roman Gushchin
2020-10-01 0:27 ` [PATCH v4 3/4] mm: introduce page memcg flags Roman Gushchin
2020-10-01 13:44 ` Johannes Weiner
2020-10-01 0:27 ` [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag Roman Gushchin
2020-10-01 13:48 ` Johannes Weiner
2020-10-01 17:00 ` Michal Koutný
2020-10-01 17:27 ` Johannes Weiner [this message]
2020-10-02 10:03 ` Michal Koutný
2020-10-02 13:25 ` Johannes Weiner
2020-10-01 18:30 ` Roman Gushchin
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