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Date:   Thu, 10 Jan 2019 10:57:52 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
Cc:     akpm@linux-foundation.org, hannes@cmpxchg.org,
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        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 0/3] mm: Reduce IO by improving algorithm of memcg
 pagecache pages eviction
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On Thu 10-01-19 12:42:02, Kirill Tkhai wrote:
[...]
> In general, I think a some time useful design is not a Bible, that nobody
> is allowed to change. We should not limit us in something, in case of this
> has a sense and may be useful. This is just a note in general.

But any semantic exported to the userspace and real application
depending on it is carved in stone for ever. And this is the case here I
am afraid. So if we really need some sort of soft unmapping or
reparenting a memory from a memcg then we really need to find a
different way. I do not see a straightforward way right now TBH.
-- 
Michal Hocko
SUSE Labs