Messages in this thread | | | Subject | Re: kernel 3.2.27 on arm: WARNING: at mm/page_alloc.c:2109 __alloc_pages_nodemask+0x1d4/0x68c() | From | Eric Dumazet <> | Date | Thu, 04 Oct 2012 18:29:31 +0200 |
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On Thu, 2012-10-04 at 18:02 +0200, Maxime Bizon wrote: > On Fri, 2012-08-31 at 19:21 -0700, Hugh Dickins wrote: > > Hi, > > > Francois is right that a GFP_ATOMIC allocation from pskb_expand_head() > > is failing, which can easily happen, and cause your "failed to reallocate > > TX buffer" errors; but it's well worth looking up what's actually on > > lines 2108 and 2109 of mm/page_alloc.c in 3.2.27: > > > > if (order >= MAX_ORDER) { > > WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)); > > > > That was probably not a sane allocation request, it has gone out of range: > > maybe the skb header is even corrupted. If you're lucky, it might be > > something that netdev will recognize as already fixed. > > I have the same problem on the exact same hardware and found the cause: > > Author: Eric Dumazet <eric.dumazet@gmail.com> > Date: Tue Apr 10 20:08:39 2012 +0000 > > net: allow pskb_expand_head() to get maximum tailroom > > [ Upstream commit 87151b8689d890dfb495081f7be9b9e257f7a2df ] > > > It turns out this change has a bad side effect on drivers that uses > skb_recycle(), in that case mv643xx_eth.c > > 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. > > 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) > > skb recycling gives a small speed boost, but does not get a lot of test > coverage since only 3 drivers uses it >
Thanks Maxime
Sure we can probably fix this issue, but its really not worth the pain.
I would get rid of it, its superseded by build_skb() to get cache hot skbs anyway, and more over, rx path now uses skb->head allocated from a page fragment for optimal GRO/TCP coalescing behavior.
skb_recycle() assumes skb allocation is slow, but its not per se.
Cache line misses are expensive, thats the real issue.
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