From: Johannes Weiner <hannes@cmpxchg.org>
To: Roman Gushchin <guro@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] mm: workingset: fix vmstat counters for shadow nodes
Date: Mon, 5 Aug 2019 15:43:41 -0400 [thread overview]
Message-ID: <20190805194341.GA6260@cmpxchg.org> (raw)
In-Reply-To: <20190801233532.138743-1-guro@fb.com>
On Thu, Aug 01, 2019 at 04:35:32PM -0700, Roman Gushchin wrote:
> Memcg counters for shadow nodes are broken because the memcg pointer is
> obtained in a wrong way. The following approach is used:
> virt_to_page(xa_node)->mem_cgroup
>
> Since commit 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup
> pointer for slab pages") page->mem_cgroup pointer isn't set for slab pages,
> so memcg_from_slab_page() should be used instead.
>
> Also I doubt that it ever worked correctly: virt_to_head_page() should be
> used instead of virt_to_page(). Otherwise objects residing on tail pages
> are not accounted, because only the head page contains a valid mem_cgroup
> pointer. That was a case since the introduction of these counters by the
> commit 68d48e6a2df5 ("mm: workingset: add vmstat counter for shadow nodes").
You're right. slub uses order-2 compound pages for radix_tree_node, so
we've been underreporting shadow nodes placed in the three tail pages.
Nice catch.
> Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
prev parent reply other threads:[~2019-08-05 19:43 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 23:35 [PATCH] mm: workingset: fix vmstat counters for shadow nodes Roman Gushchin
2019-08-05 19:43 ` Johannes Weiner [this message]
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