Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20200303233550.251375-1-guro@fb.com>
In-Reply-To: <20200303233550.251375-1-guro@fb.com>
From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 3 Mar 2020 15:54:24 -0800
Message-ID: <CALvZod5c_B3akg75UmzS-0pUAmBL_9-xmztw3gEkVLZMwgPs3g@mail.gmail.com>
Subject: Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations
To:     Roman Gushchin <guro@fb.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Kernel Team <kernel-team@fb.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Bharata B Rao <bharata@linux.ibm.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Mar 3, 2020 at 3:36 PM Roman Gushchin <guro@fb.com> wrote:
>
> Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> the space for task stacks can be allocated using __vmalloc_node_range(),
> alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> second cases page->mem_cgroup pointer is set, but in the third it's
> not: memcg membership of a slab page should be determined using the
> memcg_from_slab_page() function, which looks at
> page->slab_cache->memcg_params.memcg . In this case, using
> mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> page->mem_cgroup pointer is NULL even for pages charged to a non-root
> memory cgroup.
>
> It can lead to kernel_stack per-memcg counters permanently showing 0
> on some architectures (depending on the configuration).
>
> In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> which takes a pointer to a kernel object as a first argument, uses
> mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> calls mod_memcg_state(). It allows to handle all possible
> configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> values) without spilling any memcg/kmem specifics into fork.c .
>
> Note: this patch has been first posted as a part of the new slab
> controller patchset. This is a slightly updated version: the fixes
> tag has been added and the commit log was extended by the advice
> of Johannes Weiner. Because it's a fix that makes sense by itself,
> I'm re-posting it as a standalone patch.
>
> Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>