On Mon, 2013-05-27 at 15:25 -0700, Eric Dumazet wrote:
> On Mon, 2013-05-27 at 13:39 -0400, Rik van Riel wrote:
> > On 05/26/2013 04:19 PM, atom...@redhat.com wrote:
> > > Failed GFP_ATOMIC allocations by the network stack result in dropped
> > > packets, which will be received on a subsequent retransmit, and an
> > > unnecessary, noisy warning with a kernel backtrace.
>
> This claim is wrong, only some protocols deal with retransmits.
>
> > > These warnings are harmless, but they still cause users to panic and
> > > file bug reports over dropped packets. It would be better to hide the
> > > failed allocation warnings and backtraces, and let retransmits handle
> > > dropped packets quietly.
> >
> > Yes please. Getting memory management bug reports for
> > dropped network packets got old years ago. Lets get
> > rid of those messages.
>
> I am only wondering why this path has anything needing special
> attention, over thousands of kmalloc() like call sites in the kernel.
I don't think this site is particularly special.
> If mm allocation warnings are useless, just make __GFP_NOWARN the
> default, and save us thousand of patches (adding the __GFP_NOWARN
> everywhere)
>
> Truth is : some network drivers don't deal very well with allocation
> errors. mlx4 for example absolutely wants order-2 pages in RX path, with
> no fallback to order-0 pages.
>
> So I am not against this patch, but I can not really acknowledge it,
> sorry.
I think the __alloc_skb alloc failure message is ok,
but maybe there shouldn't be something "scary" like
a dump_stack.
Maybe this site should use a trivial debug error
message like below instead.
---
net/core/skbuff.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d629891..0154803 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -231,17 +231,24 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t
gfp_mask,
struct sk_buff *skb;
u8 *data;
bool pfmemalloc;
+ bool warn_no_skb = !(gfp_mask & __GFP_NOWARN);
cache = (flags & SKB_ALLOC_FCLONE)
? skbuff_fclone_cache : skbuff_head_cache;
if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
- gfp_mask |= __GFP_MEMALLOC;
+ gfp_mask |= __GFP_MEMALLOC | __GFP_NOWARN;
/* Get the HEAD */
skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
- if (!skb)
+ if (!skb) {
+ if (warn_no_skb)
+ printk_ratelimited(KERN_DEBUG "%s: OOM from %pF via
%pF\n",
+ __func__,
+ __builtin_return_address(0),
+ __builtin_return_address(1));
goto out;
+ }
prefetchw(skb);
/* We do our best to align skb_shared_info on a separate cache
--
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