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Date: Tue, 18 Mar 2014 18:10:40 -0700
Message-ID: <CA+55aFx0ZyCVrkosgTongBrNX6mJM4B8+QZQE1p0okk8ubbv7g@mail.gmail.com>
Subject: Re: bad rss-counter message in 3.14rc5
From: Linus Torvalds <torvalds@linux-foundation.org>
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Sender: owner-linux-mm@kvack.org
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To: Hugh Dickins <hughd@google.com>
Cc: Dave Jones <davej@redhat.com>, Cyrill Gorcunov <gorcunov@gmail.com>, Sasha Levin <sasha.levin@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Linux Kernel <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Bob Liu <bob.liu@oracle.com>, Konstantin Khlebnikov <koct9i@gmail.com>

On Tue, Mar 18, 2014 at 5:38 PM, Hugh Dickins <hughd@google.com> wrote:
>
> And yes, it is possible (though very unusual) to find an anon page or
> swap entry in a VM_SHARED nonlinear mapping: coming from that horrid
> get_user_pages(write, force) case which COWs even in a shared mapping.

Hmm. Maybe we could just disallow that forced case.

It *used* to be a trivial "we can just do a COW", but that was back
when the VM was much simpler and we had no rmap's etc. So "that horrid
case" used to be a simple hack that wasn't painful. But I suspect we
could very easily just fail it instead of forcing a COW, if that would
make it simpler for the VM code.

               Linus

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