From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD98CC282C4 for ; Thu, 7 Feb 2019 16:56:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9F6E321908 for ; Thu, 7 Feb 2019 16:56:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726941AbfBGQ4B (ORCPT ); Thu, 7 Feb 2019 11:56:01 -0500 Received: from mga18.intel.com ([134.134.136.126]:36635 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726319AbfBGQ4B (ORCPT ); Thu, 7 Feb 2019 11:56:01 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2019 08:56:00 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,344,1544515200"; d="scan'208";a="113169778" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga007.jf.intel.com with ESMTP; 07 Feb 2019 08:56:00 -0800 Message-ID: Subject: Re: [RFC PATCH 0/4] kvm: Report unused guest pages to host From: Alexander Duyck To: Nitesh Narayan Lal , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: rkrcmar@redhat.com, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, Luiz Capitulino , David Hildenbrand Date: Thu, 07 Feb 2019 08:56:00 -0800 In-Reply-To: References: <20190204181118.12095.38300.stgit@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-2.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2019-02-07 at 09:48 -0500, Nitesh Narayan Lal wrote: > On 2/4/19 1:15 PM, Alexander Duyck wrote: > > This patch set provides a mechanism by which guests can notify the host of > > pages that are not currently in use. Using this data a KVM host can more > > easily balance memory workloads between guests and improve overall system > > performance by avoiding unnecessary writing of unused pages to swap. > > > > In order to support this I have added a new hypercall to provided unused > > page hints and made use of mechanisms currently used by PowerPC and s390 > > architectures to provide those hints. To reduce the overhead of this call > > I am only using it per huge page instead of of doing a notification per 4K > > page. By doing this we can avoid the expense of fragmenting higher order > > pages, and reduce overall cost for the hypercall as it will only be > > performed once per huge page. > > > > Because we are limiting this to huge pages it was necessary to add a > > secondary location where we make the call as the buddy allocator can merge > > smaller pages into a higher order huge page. > > > > This approach is not usable in all cases. Specifically, when KVM direct > > device assignment is used, the memory for a guest is permanently assigned > > to physical pages in order to support DMA from the assigned device. In > > this case we cannot give the pages back, so the hypercall is disabled by > > the host. > > > > Another situation that can lead to issues is if the page were accessed > > immediately after free. For example, if page poisoning is enabled the > > guest will populate the page *after* freeing it. In this case it does not > > make sense to provide a hint about the page being freed so we do not > > perform the hypercalls from the guest if this functionality is enabled. > > Hi Alexander, > > Did you get a chance to look at my v8 posting of Guest Free Page Hinting > [1]? > Considering both the solutions are trying to solve the same problem. It > will be great if we can collaborate and come up with a unified solution. > > [1] https://lkml.org/lkml/2019/2/4/993 I haven't had a chance to review these yet. I'll try to take a look later today and provide review notes based on what I find. Thanks. - Alex