From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 2ED7D6B0269 for ; Wed, 11 Jul 2018 09:56:02 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id u18-v6so16305437pfh.21 for ; Wed, 11 Jul 2018 06:56:02 -0700 (PDT) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTPS id z28-v6si17275469pfa.161.2018.07.11.06.56.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Jul 2018 06:56:01 -0700 (PDT) From: "Wang, Wei W" Subject: RE: [PATCH v35 1/5] mm: support to get hints of free page blocks Date: Wed, 11 Jul 2018 13:55:15 +0000 Message-ID: <286AC319A985734F985F78AFA26841F7396EEFD8@SHSMSX101.ccr.corp.intel.com> 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> <20180711110949.GJ20050@dhcp22.suse.cz> In-Reply-To: <20180711110949.GJ20050@dhcp22.suse.cz> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko 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 Wednesday, July 11, 2018 7:10 PM, Michal Hocko wrote: > 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. >=20 > 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 Sounds good to me, thanks. >=20 > > I plan to let free page allocation stop when the remaining system free > > memory becomes close to min_free_kbytes (prevent swapping). >=20 > ~__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. "close to min_free_kbytes" - I meant when doing the allocations, we intenti= onally reserve some small amount of memory, e.g. 2 free page blocks of "MAX= _ORDER - 1". So when other applications happen to do some allocation, they = may easily get some from the reserved memory left on the free list. Without= that reserved memory, other allocation may cause the system free memory be= low the WMARK[MIN], and kswapd would start to do swapping. This is actually= just a small optimization to reduce the probability of causing swapping (n= ice to have, but not mandatary because we will allocate free page blocks on= e by one). > 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. With less free memory, the improvement becomes less, but should be nicer th= an no optimization. For example, the Linux build workload would cause 4~5 G= B (out of 8GB) memory to be used as page cache at the final stage, there is= still ~44% live migration time reduction. Since we have many cloud customers interested in this feature, I think we c= an let them test the usefulness. Best, Wei