Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753763AbbERQ2p (ORCPT ); Mon, 18 May 2015 12:28:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43563 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751277AbbERQ2m (ORCPT ); Mon, 18 May 2015 12:28:42 -0400 Date: Mon, 18 May 2015 18:28:39 +0200 From: "Michael S. Tsirkin" To: Andrey Korolyov Cc: Eric Northup , Paolo Bonzini , Igor Mammedov , Linux Kernel Mailing List , KVM , netdev@vger.kernel.org Subject: Re: [PATCH] vhost: support upto 509 memory regions Message-ID: <20150518182723-mutt-send-email-mst@redhat.com> References: <1423842599-5174-1-git-send-email-imammedo@redhat.com> <20150217090242.GA20254@redhat.com> <54E31F24.1060705@redhat.com> <20150217123212.GA6362@redhat.com> <20150218042739.GA22891@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3400 Lines: 87 On Mon, May 18, 2015 at 07:22:34PM +0300, Andrey Korolyov wrote: > On Wed, Feb 18, 2015 at 7:27 AM, Michael S. Tsirkin wrote: > > On Tue, Feb 17, 2015 at 04:53:45PM -0800, Eric Northup wrote: > >> On Tue, Feb 17, 2015 at 4:32 AM, Michael S. Tsirkin wrote: > >> > On Tue, Feb 17, 2015 at 11:59:48AM +0100, Paolo Bonzini wrote: > >> >> > >> >> > >> >> On 17/02/2015 10:02, Michael S. Tsirkin wrote: > >> >> > > Increasing VHOST_MEMORY_MAX_NREGIONS from 65 to 509 > >> >> > > to match KVM_USER_MEM_SLOTS fixes issue for vhost-net. > >> >> > > > >> >> > > Signed-off-by: Igor Mammedov > >> >> > > >> >> > This scares me a bit: each region is 32byte, we are talking > >> >> > a 16K allocation that userspace can trigger. > >> >> > >> >> What's bad with a 16K allocation? > >> > > >> > It fails when memory is fragmented. > >> > > >> >> > How does kvm handle this issue? > >> >> > >> >> It doesn't. > >> >> > >> >> Paolo > >> > > >> > I'm guessing kvm doesn't do memory scans on data path, > >> > vhost does. > >> > > >> > qemu is just doing things that kernel didn't expect it to need. > >> > > >> > Instead, I suggest reducing number of GPA<->HVA mappings: > >> > > >> > you have GPA 1,5,7 > >> > map them at HVA 11,15,17 > >> > then you can have 1 slot: 1->11 > >> > > >> > To avoid libc reusing the memory holes, reserve them with MAP_NORESERVE > >> > or something like this. > >> > >> This works beautifully when host virtual address bits are more > >> plentiful than guest physical address bits. Not all architectures > >> have that property, though. > > > > AFAIK this is pretty much a requirement for both kvm and vhost, > > as we require each guest page to also be mapped in qemu memory. > > > >> > We can discuss smarter lookup algorithms but I'd rather > >> > userspace didn't do things that we then have to > >> > work around in kernel. > >> > > >> > > >> > -- > >> > MST > >> > -- > >> > To unsubscribe from this list: send the line "unsubscribe kvm" in > >> > the body of a message to majordomo@vger.kernel.org > >> > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > > To unsubscribe from this list: send the line "unsubscribe netdev" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > Hello, > > any chance of getting the proposed patch in the mainline? Though it > seems that most users will not suffer from relatively slot number > ceiling (they can decrease slot 'granularity' for larger VMs and > vice-versa), fine slot size, 256M or even 128M, with the large number > of slots can be useful for a certain kind of tasks for an > orchestration systems. I`ve made a backport series of all seemingly > interesting memslot-related improvements to a 3.10 branch, is it worth > to be tested with straighforward patch like one from above, with > simulated fragmentation of allocations in host? I'd rather people worked on the 1:1 mapping, it will also speed up lookups. I'm concerned if I merge this one, motivation for people to work on the right fix will disappear. -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/