linux-kernel - Re: bad rss-counter message in 3.14rc5

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

On Tue, Mar 18, 2014 at 5:38 PM, Hugh Dickins <hughd@...gle.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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