From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id 18C1F6B02C3 for ; Tue, 20 Jun 2017 14:26:24 -0400 (EDT) Received: by mail-qk0-f198.google.com with SMTP id a199so31862064qkb.9 for ; Tue, 20 Jun 2017 11:26:24 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id i20si755795qtf.145.2017.06.20.11.26.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Jun 2017 11:26:23 -0700 (PDT) Date: Tue, 20 Jun 2017 21:26:15 +0300 From: "Michael S. Tsirkin" Subject: Re: [PATCH v11 4/6] mm: function to offer a page block on the free list Message-ID: <20170620212107-mutt-send-email-mst@kernel.org> 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> <1497979740.20270.102.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1497979740.20270.102.camel@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: David Hildenbrand , 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, 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, Nitesh Narayan Lal On Tue, Jun 20, 2017 at 01:29:00PM -0400, Rik van Riel wrote: > On Tue, 2017-06-20 at 18:49 +0200, David Hildenbrand wrote: > > On 20.06.2017 18:44, Rik van Riel wrote: > > > > 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. > > I agree with that. Let me go into some more detail of > what Nitesh is implementing: > > 1) In arch_free_page, the being-freed page is added > to a per-cpu set of freed pages. > 2) Once that set is full, arch_free_pages goes into a > slow path, which: > 2a) Iterates over the set of freed pages, and > 2b) Checks whether they are still free, and > 2c) Adds the still free pages to a list that is > to be passed to the hypervisor, to be MADV_FREEd. > 2d) Makes that hypercall. > > Meanwhile all arch_alloc_pages has to do is make sure it > does not allocate a page while it is currently being > MADV_FREEd on the hypervisor side. > > The code Wei is working on looks like it could be > suitable for steps (2c) and (2d) above. Nitesh already > has code for steps 1 through 2b. > > -- > All rights reversed So my question is this: Wei posted these numbers for balloon inflation times: inflating 7GB of an 8GB idle guest: 1) allocating pages (6.5%) 2) sending PFNs to host (68.3%) 3) address translation (6.1%) 4) madvise (19%) It takes about 4126ms for the inflating process to complete. It seems that this is an excessive amount of time to stay under a lock. What are your estimates for Nitesh's work? -- MST -- 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