From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Li, Liang Z" Subject: RE: [virtio-dev] Re: [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process Date: Tue, 2 Aug 2016 00:28:19 +0000 Message-ID: References: <1469582616-5729-1-git-send-email-liang.z.li@intel.com> <1469582616-5729-5-git-send-email-liang.z.li@intel.com> <5798DB49.7030803@intel.com> <20160728044000-mutt-send-email-mst@kernel.org> <20160729003759-mutt-send-email-mst@kernel.org> <579BB30B.2040704@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <579BB30B.2040704@intel.com> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Hansen, Dave" , "Michael S. Tsirkin" Cc: "virtio-dev@lists.oasis-open.org" , "kvm@vger.kernel.org" , Amit Shah , "qemu-devel@nongnu.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Vlastimil Babka , Paolo Bonzini , Andrew Morton , "virtualization@lists.linux-foundation.org" , Mel Gorman , "dgilbert@redhat.com" List-Id: virtualization@lists.linuxfoundation.org > > It's only small because it makes you rescan the free list. > > So maybe you should do something else. > > I looked at it a bit. Instead of scanning the free list, how about > > scanning actual page structures? If page is unused, pass it to host. > > Solves the problem of rescanning multiple times, does it not? > > FWIW, I think the new data structure needs some work. > > Before, we had a potentially very long list of 4k areas. Now, we've just got a > very large bitmap. The bitmap might not even be very dense if we are > ballooning relatively few things. > > Can I suggest an alternate scheme? I think you actually need a hybrid > scheme that has bitmaps but also allows more flexibility in the pfn ranges. > The payload could be a number of records each containing 3 things: > > pfn, page order, length of bitmap (maybe in powers of 2) > > Each record is followed by the bitmap. Or, if the bitmap length is 0, > immediately followed by another record. A bitmap length of 0 implies a > bitmap with the least significant bit set. Page order specifies how many > pages each bit represents. > > This scheme could easily encode the new data structure you are proposing > by just setting pfn=0, order=0, and a very long bitmap length. But, it could > handle sparse bitmaps much better *and* represent large pages much more > efficiently. > > There's plenty of space to fit a whole record in 64 bits. I like your idea and it's more flexible, and it's very useful if we want to optimize the page allocating stage further. I believe the memory fragmentation will not be very serious, so the performance won't be too bad in the worst case. Thanks! Liang