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Date: Mon, 23 Oct 2017 13:54:50 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Neha Agarwal <nehaagarwal@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Rientjes <rientjes@google.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>, Kemi Wang <kemi.wang@intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Shaohua Li <shli@fb.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, cgroups@vger.kernel.org
Subject: Re: [RFC PATCH] mm, thp: make deferred_split_shrinker memcg-aware
Message-ID: <20171023105450.jv4qerpzlrodfws6@node.shutemov.name>
References: <20171019200323.42491-1-nehaagarwal@google.com>
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On Thu, Oct 19, 2017 at 01:03:23PM -0700, Neha Agarwal wrote:
> deferred_split_shrinker is NUMA aware. Making it memcg-aware if
> CONFIG_MEMCG is enabled to prevent shrinking memory of memcg(s) that are
> not under memory pressure. This change isolates memory pressure across
> memcgs from deferred_split_shrinker perspective, by not prematurely
> splitting huge pages for the memcg that is not under memory pressure.
> 
> Note that a pte-mapped compound huge page charge is not moved to the dst
> memcg on task migration. Look mem_cgroup_move_charge_pte_range() for
> more information. Thus, mem_cgroup_move_account doesn't get called on
> pte-mapped compound huge pages, hence we do not need to transfer the
> page from source-memcg's split to destinations-memcg's split_queue.
> 
> Tested: Ran two copies of a microbenchmark with partially unmapped
> thp(s) in two separate memory cgroups. When first memory cgroup is put
> under memory pressure, it's own thp(s) split. Other memcg's thp(s)
> remain intact.
> 
> Current implementation is not NUMA aware if MEMCG is compiled. If it is
> important to have this shrinker both NUMA and MEMCG aware, I can work on
> that.  Some feedback on this front will be useful.

I thin, this should be done. That's strange compromise -- memcg vs NUMA.
And I think solving will help a lot with ifdefs.

-- 
 Kirill A. Shutemov