From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753065AbeDRRt6 (ORCPT ); Wed, 18 Apr 2018 13:49:58 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60198 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751692AbeDRRt4 (ORCPT ); Wed, 18 Apr 2018 13:49:56 -0400 Date: Wed, 18 Apr 2018 13:49:54 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Eric Dumazet cc: "David S. Miller" , Eric Dumazet , Ben Hutchings , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org Subject: Re: [PATCH] net: don't use kvzalloc for DMA memory In-Reply-To: <5f4e1286-b79f-0b9f-9a30-47d7654f3889@gmail.com> Message-ID: References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <5f4e1286-b79f-0b9f-9a30-47d7654f3889@gmail.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 18 Apr 2018, Eric Dumazet wrote: > > > On 04/18/2018 09:44 AM, Mikulas Patocka wrote: > > > > > > On Wed, 18 Apr 2018, Eric Dumazet wrote: > > > >> > >> > >> On 04/18/2018 07:34 AM, Mikulas Patocka wrote: > >>> The patch 74d332c13b21 changes alloc_netdev_mqs to use vzalloc if kzalloc > >>> fails (later patches change it to kvzalloc). > >>> > >>> The problem with this is that if the vzalloc function is actually used, > >>> virtio_net doesn't work (because it expects that the extra memory should > >>> be accessible with DMA-API and memory allocated with vzalloc isn't). > >>> > >>> This patch changes it back to kzalloc and adds a warning if the allocated > >>> size is too large (the allocation is unreliable in this case). > >>> > >>> Signed-off-by: Mikulas Patocka > >>> Fixes: 74d332c13b21 ("net: extend net_device allocation to vmalloc()") > >>> > >>> --- > >>> net/core/dev.c | 3 ++- > >>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>> > >>> Index: linux-2.6/net/core/dev.c > >>> =================================================================== > >>> --- linux-2.6.orig/net/core/dev.c 2018-04-16 21:08:36.000000000 +0200 > >>> +++ linux-2.6/net/core/dev.c 2018-04-18 16:24:43.000000000 +0200 > >>> @@ -8366,7 +8366,8 @@ struct net_device *alloc_netdev_mqs(int > >>> /* ensure 32-byte alignment of whole construct */ > >>> alloc_size += NETDEV_ALIGN - 1; > >>> > >>> - p = kvzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL); > >>> + WARN_ON(alloc_size > PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER); > >>> + p = kzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL); > >>> if (!p) > >>> return NULL; > >>> > >>> > >> > >> Since when a net_device needs to be in DMA zone ??? > >> > >> I would rather fix virtio_net, this looks very suspect to me. > >> > >> Each virtio_net should probably allocate the exact amount of DMA-memory it wants, > >> instead of expecting core networking stack to have a huge chunk of DMA-memory for everything. > > > > The structure net_device is followed by arbitrary driver-specific data > > (accessible with the function netdev_priv). And for virtio-net, these > > driver-specific data must be in DMA memory. > > I get that, but how is the original xenvif problem will be solved ? > > Your patch would add a bug in some other driver(s) > > I suggest that virtio_net clearly identifies which part needs a specific allocation > and does its itself, instead of abusing the netdev_priv storage. > > Ie use a pointer to a block of memory, allocated by virtio_net, for virtio_net. There are drivers that need to do DMA to driver-specific area. And there are drivers that need driver-specific area larger than kmalloc limit. These are conflicting requirements and one of those drivers must be changed. I suggest to change the drivers that need large driver-specific area. That's why I added the WARN_ON, so that they can be identified. Mikulas