linux-kernel - Re: [RFC PATCH] mm, thp: make deferred_split

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Date:   Mon, 23 Oct 2017 13:54:50 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Neha Agarwal <nehaagarwal@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kemi Wang <kemi.wang@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Shaohua Li <shli@...com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH] mm, thp: make deferred_split_shrinker memcg-aware

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