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Date: Tue, 7 Oct 2014 08:47:59 -0400
Message-ID: <CA+55aFxAOYBny+QwXfkPy-P3rs-RPr5SLYLcPNBiFO3waBXtQA@mail.gmail.com>
Subject: Re: [PATCH 10/17] mm: rmap preparation for remap_anon_pages
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, qemu-devel@nongnu.org, KVM list <kvm@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Linux API <linux-api@vger.kernel.org>, Andres Lagar-Cavilla <andreslc@google.com>, Dave Hansen <dave@sr71.net>, Paolo Bonzini <pbonzini@redhat.com>, Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>, Andy Lutomirski <luto@amacapital.net>, Andrew Morton <akpm@linux-foundation.org>, Sasha Levin <sasha.levin@oracle.com>, Hugh Dickins <hughd@google.com>, Peter Feiner <pfeiner@google.com>, Christopher Covington <cov@codeaurora.org>, Johannes Weiner <hannes@cmpxchg.org>, Android Kernel Team <kernel-team@android.com>, Robert Love <rlove@google.com>, Dmitry Adamushko <dmitry.adamushko@gmail.com>, Neil Brown <neilb@suse.de>, Mike Hommey <mh@glandium.org>, Taras Glek <tglek@mozilla.com>, Jan Kara <jack@suse.cz>, KOSAKI Motohiro <kosaki.motohiro@gmail.com>, Michel Lespinasse <walken@google.com>, Minchan Kim <minchan@kernel.org>, Keith Packard <keithp@keithp.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>, Isaku Yamahata <yamahata@valinux.co.jp>, Anthony Liguori <anthony@codemonkey.ws>, Stefan Hajnoczi <stefanha@gmail.com>, Wenchao Xia <wenchaoqemu@gmail.com>, Andrew Jones <drjones@redhat.com>, Juan Quintela <quintela@redhat.com>

On Mon, Oct 6, 2014 at 12:41 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
>
> Of course if somebody has better ideas on how to resolve an anonymous
> userfault they're welcome.

So I'd *much* rather have a "write()" style interface (ie _copying_
bytes from user space into a newly allocated page that gets mapped)
than a "remap page" style interface

remapping anonymous pages involves page table games that really aren't
necessarily a good idea, and tlb invalidates for the old page etc.
Just don't do it.

           Linus

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