[{"id":1772078,"web_url":"http://patchwork.ozlabs.org/comment/1772078/","msgid":"<54984f46-f50b-8306-2229-15ea96cea7d6@redhat.com>","list_archive_url":null,"date":"2017-09-20T17:13:05","subject":"Re: [Qemu-devel] [PATCH qemu v4 15/18] memory: Share special empty\n\tFlatView","submitter":{"id":2701,"url":"http://patchwork.ozlabs.org/api/people/2701/","name":"Paolo Bonzini","email":"pbonzini@redhat.com"},"content":"On 20/09/2017 13:46, Alexey Kardashevskiy wrote:\n> This shares an cached empty FlatView among address spaces. The empty\n> FV is used every time when a root MR renders into a FV without memory\n> sections which happens when MR or its children are not enabled or\n> zero-sized. The empty_view is not NULL to keep the rest of memory\n> API intact; it also has a dispatch tree for the same reason.\n> \n> On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves\n> the amount of FlatView's in use (557 -> 260) and dispatch tables\n> (~800000 -> ~370000), however the total memory footprint is pretty much\n> the same as RCU is holding all these temporary FVs which are created\n> (and then released) to make sure that they are empty and can be replaced\n> with @empty_view.\n> \n> Signed-off-by: Alexey Kardashevskiy \n> ---\n> memory.c | 14 ++++++++++++++\n> 1 file changed, 14 insertions(+)\n> \n> diff --git a/memory.c b/memory.c\n> index 4add0fd030..92b1304a20 100644\n> --- a/memory.c\n> +++ b/memory.c\n> @@ -48,6 +48,7 @@ static QTAILQ_HEAD(, AddressSpace) address_spaces\n> = QTAILQ_HEAD_INITIALIZER(address_spaces);\n> \n> static GHashTable *flat_views;\n> +static FlatView *empty_view;\n> \n> typedef struct AddrRange AddrRange;\n> \n> @@ -755,6 +756,19 @@ static FlatView *generate_memory_topology(MemoryRegion *mr)\n> }\n> flatview_simplify(view);\n> \n> + if (!view->nr) {\n> + flatview_unref(view);\n\nThis can be changed to flatview_destroy directly to avoid overloading\nRCU with all these temporary FlatViews.\n\nPaolo\n\n> + if (!empty_view) {\n> + empty_view = flatview_new(NULL);\n> + }\n> + view = empty_view;\n> + flatview_ref(view);\n> + }\n> +\n> + if (view->dispatch) {\n> + return view;\n> + }\n> +\n> view->dispatch = address_space_dispatch_new(view);\n> for (i = 0; i < view->nr; i++) {\n> MemoryRegionSection mrs =\n>","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@bilbo.ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=pass (mailfrom) smtp.mailfrom=nongnu.org\n\t(client-ip=2001:4830:134:3::11; helo=lists.gnu.org;\n\tenvelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n\treceiver=)","ext-mx01.extmail.prod.ext.phx2.redhat.com;\n\tdmarc=none (p=none dis=none) header.from=redhat.com","ext-mx01.extmail.prod.ext.phx2.redhat.com;\n\tspf=fail smtp.mailfrom=pbonzini@redhat.com"],"Received":["from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11])\n\t(using TLSv1 with cipher AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3xy5tX3cpHz9s0Z\n\tfor ;\n\tThu, 21 Sep 2017 03:13:39 +1000 (AEST)","from localhost ([::1]:49854 helo=lists.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.71) (envelope-from\n\t)\n\tid 1duiZ6-0006Z1-V4\n\tfor incoming@patchwork.ozlabs.org; Wed, 20 Sep 2017 13:13:36 -0400","from eggs.gnu.org ([2001:4830:134:3::10]:45958)\n\tby lists.gnu.org with esmtp (Exim 4.71)\n\t(envelope-from ) id 1duiYi-0006YL-Mb\n\tfor qemu-devel@nongnu.org; Wed, 20 Sep 2017 13:13:13 -0400","from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)\n\t(envelope-from ) id 1duiYg-0008A2-0D\n\tfor qemu-devel@nongnu.org; Wed, 20 Sep 2017 13:13:12 -0400","from mx1.redhat.com ([209.132.183.28]:54828)\n\tby eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32)\n\t(Exim 4.71) (envelope-from ) id 1duiYf-000891-Pd\n\tfor qemu-devel@nongnu.org; Wed, 20 Sep 2017 13:13:09 -0400","from smtp.corp.redhat.com\n\t(int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15])\n\t(using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby mx1.redhat.com (Postfix) with ESMTPS id 328E081E18;\n\tWed, 20 Sep 2017 17:13:08 +0000 (UTC)","from [10.36.117.211] (ovpn-117-211.ams2.redhat.com [10.36.117.211])\n\tby smtp.corp.redhat.com (Postfix) with ESMTPS id 88D285D75A;\n\tWed, 20 Sep 2017 17:13:07 +0000 (UTC)"],"DMARC-Filter":"OpenDMARC Filter v1.3.2 mx1.redhat.com 328E081E18","To":"Alexey Kardashevskiy , qemu-devel@nongnu.org","References":"<20170920114637.42004-1-aik@ozlabs.ru>\n\t<20170920114637.42004-16-aik@ozlabs.ru>","From":"Paolo Bonzini ","Message-ID":"<54984f46-f50b-8306-2229-15ea96cea7d6@redhat.com>","Date":"Wed, 20 Sep 2017 19:13:05 +0200","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101\n\tThunderbird/52.3.0","MIME-Version":"1.0","In-Reply-To":"<20170920114637.42004-16-aik@ozlabs.ru>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-US","Content-Transfer-Encoding":"7bit","X-Scanned-By":"MIMEDefang 2.79 on 10.5.11.15","X-Greylist":"Sender IP whitelisted, not delayed by milter-greylist-4.5.16\n\t(mx1.redhat.com [10.5.110.25]);\n\tWed, 20 Sep 2017 17:13:08 +0000 (UTC)","X-detected-operating-system":"by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic]\n\t[fuzzy]","X-Received-From":"209.132.183.28","Subject":"Re: [Qemu-devel] [PATCH qemu v4 15/18] memory: Share special empty\n\tFlatView","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.21","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"\"Qemu-devel\"\n\t"}},{"id":1772319,"web_url":"http://patchwork.ozlabs.org/comment/1772319/","msgid":"<7a46de37-95dd-d662-3a4c-05421f5e8f1a@ozlabs.ru>","list_archive_url":null,"date":"2017-09-20T23:48:10","subject":"Re: [Qemu-devel] [PATCH qemu v4 15/18] memory: Share special empty\n\tFlatView","submitter":{"id":7621,"url":"http://patchwork.ozlabs.org/api/people/7621/","name":"Alexey Kardashevskiy","email":"aik@ozlabs.ru"},"content":"On 21/09/17 03:13, Paolo Bonzini wrote:\n> On 20/09/2017 13:46, Alexey Kardashevskiy wrote:\n>> This shares an cached empty FlatView among address spaces. The empty\n>> FV is used every time when a root MR renders into a FV without memory\n>> sections which happens when MR or its children are not enabled or\n>> zero-sized. The empty_view is not NULL to keep the rest of memory\n>> API intact; it also has a dispatch tree for the same reason.\n>>\n>> On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves\n>> the amount of FlatView's in use (557 -> 260) and dispatch tables\n>> (~800000 -> ~370000), however the total memory footprint is pretty much\n>> the same as RCU is holding all these temporary FVs which are created\n>> (and then released) to make sure that they are empty and can be replaced\n>> with @empty_view.\n>>\n>> Signed-off-by: Alexey Kardashevskiy \n>> ---\n>> memory.c | 14 ++++++++++++++\n>> 1 file changed, 14 insertions(+)\n>>\n>> diff --git a/memory.c b/memory.c\n>> index 4add0fd030..92b1304a20 100644\n>> --- a/memory.c\n>> +++ b/memory.c\n>> @@ -48,6 +48,7 @@ static QTAILQ_HEAD(, AddressSpace) address_spaces\n>> = QTAILQ_HEAD_INITIALIZER(address_spaces);\n>> \n>> static GHashTable *flat_views;\n>> +static FlatView *empty_view;\n>> \n>> typedef struct AddrRange AddrRange;\n>> \n>> @@ -755,6 +756,19 @@ static FlatView *generate_memory_topology(MemoryRegion *mr)\n>> }\n>> flatview_simplify(view);\n>> \n>> + if (!view->nr) {\n>> + flatview_unref(view);\n> \n> This can be changed to flatview_destroy directly to avoid overloading\n> RCU with all these temporary FlatViews.\n\n\nYeah, this or just allocate every new FlatView on the stack first, I\nthought about this a second after I posted this.\n\n\n> \n> Paolo\n> \n>> + if (!empty_view) {\n>> + empty_view = flatview_new(NULL);\n>> + }\n>> + view = empty_view;\n>> + flatview_ref(view);\n>> + }\n>> +\n>> + if (view->dispatch) {\n>> + return view;\n>> + }\n>> +\n>> view->dispatch = address_space_dispatch_new(view);\n>> for (i = 0; i < view->nr; i++) {\n>> MemoryRegionSection mrs =\n>>\n>","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@bilbo.ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=pass (mailfrom) smtp.mailfrom=nongnu.org\n\t(client-ip=2001:4830:134:3::11; helo=lists.gnu.org;\n\tenvelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n\treceiver=)","ozlabs.org;\n\tdkim=fail reason=\"signature verification failed\" (2048-bit key;\n\tunprotected) header.d=ozlabs-ru.20150623.gappssmtp.com\n\theader.i=@ozlabs-ru.20150623.gappssmtp.com\n\theader.b=\"e5SJVKV+\"; dkim-atps=neutral"],"Received":["from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11])\n\t(using TLSv1 with cipher AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 3xyGfR1TGBz9s7g\n\tfor ;\n\tThu, 21 Sep 2017 09:48:45 +1000 (AEST)","from localhost ([::1]:51123 helo=lists.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.71) (envelope-from\n\t)\n\tid 1duojS-00088l-LL\n\tfor incoming@patchwork.ozlabs.org; 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\n\tWed, 20 Sep 2017 16:48:14 -0700 (PDT)","To":"Paolo Bonzini , qemu-devel@nongnu.org","References":"<20170920114637.42004-1-aik@ozlabs.ru>\n\t<20170920114637.42004-16-aik@ozlabs.ru>\n\t<54984f46-f50b-8306-2229-15ea96cea7d6@redhat.com>","From":"Alexey Kardashevskiy ","Message-ID":"<7a46de37-95dd-d662-3a4c-05421f5e8f1a@ozlabs.ru>","Date":"Thu, 21 Sep 2017 09:48:10 +1000","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101\n\tThunderbird/52.2.1","MIME-Version":"1.0","In-Reply-To":"<54984f46-f50b-8306-2229-15ea96cea7d6@redhat.com>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-AU","Content-Transfer-Encoding":"7bit","X-detected-operating-system":"by eggs.gnu.org: Genre and OS details not\n\trecognized.","X-Received-From":"2607:f8b0:400e:c05::242","Subject":"Re: [Qemu-devel] [PATCH qemu v4 15/18] memory: Share special empty\n\tFlatView","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.21","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"\"Qemu-devel\"\n\t"}}]