From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id D8A176B0003 for ; Wed, 11 Jul 2018 07:09:53 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id l1-v6so1858665edi.11 for ; Wed, 11 Jul 2018 04:09:53 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c4-v6si3154571edb.348.2018.07.11.04.09.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Jul 2018 04:09:52 -0700 (PDT) Date: Wed, 11 Jul 2018 13:09:49 +0200 From: Michal Hocko 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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