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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 9A75CC282C2 for ; Thu, 7 Feb 2019 19:02:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69D112086C for ; Thu, 7 Feb 2019 19:02:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726915AbfBGTCC (ORCPT ); Thu, 7 Feb 2019 14:02:02 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43104 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726319AbfBGTCB (ORCPT ); Thu, 7 Feb 2019 14:02:01 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 90D8010FA7; Thu, 7 Feb 2019 19:02:00 +0000 (UTC) Received: from redhat.com (ovpn-123-55.rdu2.redhat.com [10.10.123.55]) by smtp.corp.redhat.com (Postfix) with SMTP id EC60060BE0; Thu, 7 Feb 2019 19:01:43 +0000 (UTC) Date: Thu, 7 Feb 2019 14:01:43 -0500 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: Nitesh Narayan Lal , kvm list , LKML , Paolo Bonzini , lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, Yang Zhang , riel@surriel.com, david@redhat.com, dodgen@google.com, Konrad Rzeszutek Wilk , dhildenb@redhat.com, Andrea Arcangeli Subject: Re: [RFC][Patch v8 6/7] KVM: Enables the kernel to isolate and report free pages Message-ID: <20190207135511-mutt-send-email-mst@kernel.org> References: <20190204201854.2328-1-nitesh@redhat.com> <20190204201854.2328-7-nitesh@redhat.com> <20190205153607-mutt-send-email-mst@kernel.org> <20190205165514-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 07 Feb 2019 19:02:00 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 07, 2019 at 09:43:44AM -0800, Alexander Duyck wrote: > On Tue, Feb 5, 2019 at 3:21 PM Michael S. Tsirkin wrote: > > > > On Tue, Feb 05, 2019 at 04:54:03PM -0500, Nitesh Narayan Lal wrote: > > > > > > On 2/5/19 3:45 PM, Michael S. Tsirkin wrote: > > > > On Mon, Feb 04, 2019 at 03:18:53PM -0500, Nitesh Narayan Lal wrote: > > > >> This patch enables the kernel to scan the per cpu array and > > > >> compress it by removing the repetitive/re-allocated pages. > > > >> Once the per cpu array is completely filled with pages in the > > > >> buddy it wakes up the kernel per cpu thread which re-scans the > > > >> entire per cpu array by acquiring a zone lock corresponding to > > > >> the page which is being scanned. If the page is still free and > > > >> present in the buddy it tries to isolate the page and adds it > > > >> to another per cpu array. > > > >> > > > >> Once this scanning process is complete and if there are any > > > >> isolated pages added to the new per cpu array kernel thread > > > >> invokes hyperlist_ready(). > > > >> > > > >> In hyperlist_ready() a hypercall is made to report these pages to > > > >> the host using the virtio-balloon framework. In order to do so > > > >> another virtqueue 'hinting_vq' is added to the balloon framework. > > > >> As the host frees all the reported pages, the kernel thread returns > > > >> them back to the buddy. > > > >> > > > >> Signed-off-by: Nitesh Narayan Lal > > > > > > > > This looks kind of like what early iterations of Wei's patches did. > > > > > > > > But this has lots of issues, for example you might end up with > > > > a hypercall per a 4K page. > > > > So in the end, he switched over to just reporting only > > > > MAX_ORDER - 1 pages. > > > You mean that I should only capture/attempt to isolate pages with order > > > MAX_ORDER - 1? > > > > > > > > Would that be a good idea for you too? > > > Will it help if we have a threshold value based on the amount of memory > > > captured instead of the number of entries/pages in the array? > > > > This is what Wei's patches do at least. > > So in the solution I had posted I was looking more at > HUGETLB_PAGE_ORDER and above as the size of pages to provide the hints > on [1]. The advantage to doing that is that you can also avoid > fragmenting huge pages which in turn can cause what looks like a > memory leak as the memory subsystem attempts to reassemble huge > pages[2]. In my mind a 2MB page makes good sense in terms of the size > of things to be performing hints on as anything smaller than that is > going to just end up being a bunch of extra work and end up causing a > bunch of fragmentation. Yes MAX_ORDER-1 is 4M. So not a lot of difference on x86. The idea behind keying off MAX_ORDER is that CPU hugepages isn't the only reason to avoid fragmentation, there's other hardware that benefits from linear physical addresses. And there are weird platforms where HUGETLB_PAGE_ORDER exceeds MAX_ORDER - 1. So from that POV keying it off MAX_ORDER makes more sense. > The only issue with limiting things on an arbitrary boundary like that > is that you have to hook into the buddy allocator to catch the cases > where a page has been merged up into that range. > > [1] https://lkml.org/lkml/2019/2/4/903 > [2] https://blog.digitalocean.com/transparent-huge-pages-and-alternative-memory-allocators/