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

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Date:   Fri, 20 Oct 2017 09:12:50 +0200
From:   Michal Hocko <mhocko@...nel.org>
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>,
        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 19-10-17 13:03:23, 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.

Why do we need this? THP pages are usually not shared between memcgs. Or
do you have a real world example where this is not the case? Your patch
is adding quite a lot of (and to be really honest very ugly) code so
there better should be a _very_ good reason to justify it. I haven't
looked very closely to the code, at least all those ifdefs in the code
are too ugly to live.
-- 
Michal Hocko
SUSE Labs