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References: <20210412225503.15119-1-longman@redhat.com> <20210412225503.15119-4-longman@redhat.com>
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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 12 Apr 2021 16:03:17 -0700
Message-ID: <CALvZod7hBvbnF3G_Hxbu3Xmfzdip_BGAh0Nr86vvN2d9xBTaSg@mail.gmail.com>
Subject: Re: [PATCH v2 3/5] mm/memcg: Cache vmstat data in percpu memcg_stock_pcp
To:     Waiman Long <longman@redhat.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        Xing Zhengjun <zhengjun.xing@linux.intel.com>
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On Mon, Apr 12, 2021 at 3:55 PM Waiman Long <longman@redhat.com> wrote:
>
> Before the new slab memory controller with per object byte charging,
> charging and vmstat data update happen only when new slab pages are
> allocated or freed. Now they are done with every kmem_cache_alloc()
> and kmem_cache_free(). This causes additional overhead for workloads
> that generate a lot of alloc and free calls.
>
> The memcg_stock_pcp is used to cache byte charge for a specific
> obj_cgroup to reduce that overhead. To further reducing it, this patch
> makes the vmstat data cached in the memcg_stock_pcp structure as well
> until it accumulates a page size worth of update or when other cached
> data change.
>
> On a 2-socket Cascade Lake server with instrumentation enabled and this
> patch applied, it was found that about 17% (946796 out of 5515184) of the
> time when __mod_obj_stock_state() is called leads to an actual call to
> mod_objcg_state() after initial boot. When doing parallel kernel build,
> the figure was about 16% (21894614 out of 139780628). So caching the
> vmstat data reduces the number of calls to mod_objcg_state() by more
> than 80%.
>
> Signed-off-by: Waiman Long <longman@redhat.com>

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