From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758389AbbCESID (ORCPT <rfc822;w@1wt.eu>);
	Thu, 5 Mar 2015 13:08:03 -0500
Received: from mx2.parallels.com ([199.115.105.18]:32904 "EHLO
	mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753880AbbCESIA (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 5 Mar 2015 13:08:00 -0500
Message-ID: <54F89B61.308@parallels.com>
Date: Thu, 5 Mar 2015 21:07:29 +0300
From: Pavel Emelyanov <xemul@parallels.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0
MIME-Version: 1.0
To: Andrea Arcangeli <aarcange@redhat.com>, <qemu-devel@nongnu.org>,
        <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-mm@kvack.org>, <linux-api@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
CC: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Sanidhya Kashyap <sanidhya.gatech@gmail.com>,
        <zhang.zhanghailiang@huawei.com>,
        Linus Torvalds <torvalds@linux-foundation.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>,
        "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
        Christopher Covington <cov@codeaurora.org>,
        Johannes Weiner <hannes@cmpxchg.org>, 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>,
        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>
Subject: Re: [PATCH 14/21] userfaultfd: mcopy_atomic|mfill_zeropage: UFFDIO_COPY|UFFDIO_ZEROPAGE
 preparation
References: <1425575884-2574-1-git-send-email-aarcange@redhat.com> <1425575884-2574-15-git-send-email-aarcange@redhat.com>
In-Reply-To: <1425575884-2574-15-git-send-email-aarcange@redhat.com>
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
X-Originating-IP: [89.169.95.100]
X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To
 US-EXCH.sw.swsoft.com (10.255.249.47)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> +static int mcopy_atomic_pte(struct mm_struct *dst_mm,
> +			    pmd_t *dst_pmd,
> +			    struct vm_area_struct *dst_vma,
> +			    unsigned long dst_addr,
> +			    unsigned long src_addr)
> +{
> +	struct mem_cgroup *memcg;
> +	pte_t _dst_pte, *dst_pte;
> +	spinlock_t *ptl;
> +	struct page *page;
> +	void *page_kaddr;
> +	int ret;
> +
> +	ret = -ENOMEM;
> +	page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
> +	if (!page)
> +		goto out;

Not a fatal thing, but still quite inconvenient. If there are two tasks that
have anonymous private VMAs that are still not COW-ed from each other, then
it will be impossible to keep the pages shared with userfault. Thus if we do
post-copy memory migration for tasks, then these guys will have their
memory COW-ed.


Thanks,
Pavel