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Date:   Mon, 2 Jul 2018 16:05:02 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>, willy@infradead.org,
        ldufour@linux.vnet.ibm.com, peterz@infradead.org, mingo@redhat.com,
        acme@kernel.org, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de,
        hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC v3 PATCH 4/5] mm: mmap: zap pages with read mmap_sem for
 large mapping
Message-ID: <20180702140502.GZ19043@dhcp22.suse.cz>
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On Fri 29-06-18 20:15:47, Andrew Morton wrote:
[...]
> Would one of your earlier designs have addressed all usecases?  I
> expect the dumb unmap-a-little-bit-at-a-time approach would have?

It has been already pointed out that this will not work. You simply
cannot drop the mmap_sem during unmap because another thread could
change the address space under your feet. So you need some form of
VM_DEAD and handle concurrent and conflicting address space operations.
-- 
Michal Hocko
SUSE Labs