linux-kernel - Re: [PATCH 10/17] mm: rmap preparation for remap_anon

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Message-ID: <CA+55aFxAOYBny+QwXfkPy-P3rs-RPr5SLYLcPNBiFO3waBXtQA@mail.gmail.com>
Date:	Tue, 7 Oct 2014 08:47:59 -0400
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	qemu-devel@...gnu.org, KVM list <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Linux API <linux-api@...r.kernel.org>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Dave Hansen <dave@...1.net>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Feiner <pfeiner@...gle.com>,
	Christopher Covington <cov@...eaurora.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Neil Brown <neilb@...e.de>, Mike Hommey <mh@...ndium.org>,
	Taras Glek <tglek@...illa.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keith Packard <keithp@...thp.com>,
	"Huangpeng (Peter)" <peter.huangpeng@...wei.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Stefan Hajnoczi <stefanha@...il.com>,
	Wenchao Xia <wenchaoqemu@...il.com>,
	Andrew Jones <drjones@...hat.com>,
	Juan Quintela <quintela@...hat.com>
Subject: Re: [PATCH 10/17] mm: rmap preparation for remap_anon_pages

On Mon, Oct 6, 2014 at 12:41 PM, Andrea Arcangeli <aarcange@...hat.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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