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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 027A9C5CFEB for ; Wed, 11 Jul 2018 11:09:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A977D20B6F for ; Wed, 11 Jul 2018 11:09:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A977D20B6F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732570AbeGKLNl (ORCPT ); Wed, 11 Jul 2018 07:13:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:51460 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726641AbeGKLNl (ORCPT ); Wed, 11 Jul 2018 07:13:41 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BBB00AD9E; Wed, 11 Jul 2018 11:09:51 +0000 (UTC) Date: Wed, 11 Jul 2018 13:09:49 +0200 From: Michal Hocko To: Wei Wang Cc: Linus Torvalds , virtio-dev@lists.oasis-open.org, Linux Kernel Mailing List , virtualization , KVM list , linux-mm , "Michael S. Tsirkin" , Andrew Morton , Paolo Bonzini , liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com, Rik van Riel , peterx@redhat.com Subject: Re: [PATCH v35 1/5] mm: support to get hints of free page blocks Message-ID: <20180711110949.GJ20050@dhcp22.suse.cz> References: <1531215067-35472-1-git-send-email-wei.w.wang@intel.com> <1531215067-35472-2-git-send-email-wei.w.wang@intel.com> <5B455D50.90902@intel.com> <20180711092152.GE20050@dhcp22.suse.cz> <5B45E17D.2090205@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5B45E17D.2090205@intel.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 11-07-18 18:52:45, Wei Wang wrote: > On 07/11/2018 05:21 PM, Michal Hocko wrote: > > On Tue 10-07-18 18:44:34, Linus Torvalds wrote: > > [...] > > > That was what I tried to encourage with actually removing the pages > > > form the page list. That would be an _incremental_ interface. You can > > > remove MAX_ORDER-1 pages one by one (or a hundred at a time), and mark > > > them free for ballooning that way. And if you still feel you have tons > > > of free memory, just continue removing more pages from the free list. > > We already have an interface for that. alloc_pages(GFP_NOWAIT, MAX_ORDER -1). > > So why do we need any array based interface? > > Yes, I'm trying to get free pages directly via alloc_pages, so there will be > no new mm APIs. OK. The above was just a rough example. In fact you would need a more complex gfp mask. I assume you only want to balloon only memory directly usable by the kernel so it will be (GFP_KERNEL | __GFP_NOWARN) & ~__GFP_RECLAIM > I plan to let free page allocation stop when the remaining system free > memory becomes close to min_free_kbytes (prevent swapping). ~__GFP_RECLAIM will make sure you are allocate as long as there is any memory without reclaim. It will not even poke the kswapd to do the background work. So I do not think you would need much more than that. But let me note that I am not really convinced how this (or previous) approach will really work in most workloads. We tend to cache heavily so there is rarely any memory free. -- Michal Hocko SUSE Labs