linux-kernel - Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

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Date:   Tue, 3 Mar 2020 15:54:24 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Bharata B Rao <bharata@...ux.ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

On Tue, Mar 3, 2020 at 3:36 PM Roman Gushchin <guro@...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@...com>

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