From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 01EE86B03EB for ; Wed, 21 Jun 2017 08:56:20 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id g46so30286902wrd.3 for ; Wed, 21 Jun 2017 05:56:19 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id o90si15996897wrc.330.2017.06.21.05.56.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Jun 2017 05:56:18 -0700 (PDT) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v5LCt4xs049409 for ; Wed, 21 Jun 2017 08:56:17 -0400 Received: from e38.co.us.ibm.com (e38.co.us.ibm.com [32.97.110.159]) by mx0b-001b2d01.pphosted.com with ESMTP id 2b7r1mby4n-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 21 Jun 2017 08:56:16 -0400 Received: from localhost by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Jun 2017 06:56:15 -0600 Subject: Re: [PATCH v11 4/6] mm: function to offer a page block on the free list References: <1497004901-30593-1-git-send-email-wei.w.wang@intel.com> <1497004901-30593-5-git-send-email-wei.w.wang@intel.com> <1497977049.20270.100.camel@redhat.com> <7b626551-6d1b-c8d5-4ef7-e357399e78dc@redhat.com> From: Christian Borntraeger Date: Wed, 21 Jun 2017 14:56:03 +0200 MIME-Version: 1.0 In-Reply-To: <7b626551-6d1b-c8d5-4ef7-e357399e78dc@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-IE Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand , Rik van Riel , Dave Hansen , Wei Wang , linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com Cc: Nitesh Narayan Lal On 06/20/2017 06:49 PM, David Hildenbrand wrote: > On 20.06.2017 18:44, Rik van Riel wrote: >> On Mon, 2017-06-12 at 07:10 -0700, Dave Hansen wrote: >> >>> The hypervisor is going to throw away the contents of these pages, >>> right? As soon as the spinlock is released, someone can allocate a >>> page, and put good data in it. What keeps the hypervisor from >>> throwing >>> away good data? >> >> That looks like it may be the wrong API, then? >> >> We already have hooks called arch_free_page and >> arch_alloc_page in the VM, which are called when >> pages are freed, and allocated, respectively. >> >> Nitesh Lal (on the CC list) is working on a way >> to efficiently batch recently freed pages for >> free page hinting to the hypervisor. >> >> If that is done efficiently enough (eg. with >> MADV_FREE on the hypervisor side for lazy freeing, >> and lazy later re-use of the pages), do we still >> need the harder to use batch interface from this >> patch? >> > David's opinion incoming: > > No, I think proper free page hinting would be the optimum solution, if > done right. This would avoid the batch interface and even turn > virtio-balloon in some sense useless. > Two reasons why I disagree: - virtio-balloon is often used as memory hotplug. (e.g. libvirts current/max memory uses virtio ballon) - free page hinting will not allow to shrink the page cache of guests (like a ballooner does) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org