From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Bizon Subject: Re: kernel 3.2.27 on arm: WARNING: at mm/page_alloc.c:2109 __alloc_pages_nodemask+0x1d4/0x68c() Date: Thu, 04 Oct 2012 19:09:33 +0200 Message-ID: <1349370573.2532.25.camel@sakura.staff.proxad.net> References: <20120829002548.GA7063@aldebaran.gro-tsen.net> <1349366521.2532.12.camel@sakura.staff.proxad.net> <1349369406.16011.82.camel@edumazet-glaptop> Reply-To: mbizon@freebox.fr Mime-Version: 1.0 Content-Type: text/plain; charset="ANSI_X3.4-1968" Content-Transfer-Encoding: 7bit Cc: David Madore , Francois Romieu , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Hugh Dickins To: Eric Dumazet Return-path: In-Reply-To: <1349369406.16011.82.camel@edumazet-glaptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 2012-10-04 at 18:50 +0200, Eric Dumazet wrote: > > Since skb_recycle() resets skb->data using (skb->head + NET_SKB_PAD), a > > recycled skb going multiple times through a path that needs to expand > > skb head will get bigger and bigger each time, and you eventually end up > > with an allocation failure. > > > > Because there is not enough headroom ? yes, on ipv6 forward path the default NET_SKB_PAD is too small, so each packet forwarded has its headroom expanded, it is then recycled and gets its original default headroom back, then it gets forwarded, expanded, ... > > An idea to fix this would be to pass needed skb size to skb_resize() and > > set skb->data to MIN(NET_SKB_PAD, (skb->end - skb->head - skb_size) / 2) > > I am trying to decode this but I cant ;) > > What is skb_resize() ? > and what do you mean setting skb->data to MIN(NET_SKB_PAD, (skb->end - > skb->head - skb_size) / 2) > > Care to explain again your idea ? damn typo, I meant skb_recycle(), and my formula is probably wrong. skb_size is passed to skb_recycle_check() to ensure the skb is at least that big. The idea is it to pass the same value to skb_recycle(), allowing it to set skb->data somewhat at the middle of skb head space (after honoring NET_SKB_PAD), that way the recycled skb won't have its head expanded again if it takes the same path. -- Maxime