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Subject[patch] ipv4: don't warn about skb ack allocation failures
On Tue, 16 Jun 2009, Justin Piszcz wrote:

> [6042655.794633] nfsd: page allocation failure. order:0, mode:0x20

That's a GFP_ATOMIC allocation.

> [6042655.794637] Pid: 7093, comm: nfsd Not tainted 2.6.29.1 #4
> [6042655.794638] Call Trace:
> [6042655.794640] <IRQ> [<ffffffff802850fd>] __alloc_pages_internal+0x3dd/0x4e0
> [6042655.794649] [<ffffffff802a738b>] cache_alloc_refill+0x2fb/0x570
> [6042655.794652] [<ffffffff802a7085>] kmem_cache_alloc+0x95/0xa0

Attempting to allocate new slab with GFP_ATOMIC, so no reclaim is
possible.

> [6042655.794655] [<ffffffff8059a969>] __alloc_skb+0x49/0x150
> [6042655.794658] [<ffffffff805dee06>] tcp_send_ack+0x26/0x120

If alloc_skb() cannot allocate a new skbuff_head_cache buffer atomically,
tcp_send_ack() easily recovers, so perhaps this should be annotated with
__GFP_NOWARN (as in the following patch).

> [6042655.794660] [<ffffffff805dcbd2>] tcp_rcv_established+0x7a2/0x920
> [6042655.794663] [<ffffffff805e417d>] tcp_v4_do_rcv+0xdd/0x210
> [6042655.794665] [<ffffffff805e4926>] tcp_v4_rcv+0x676/0x710
> [6042655.794668] [<ffffffff805c6a5c>] ip_local_deliver_finish+0x8c/0x160
> [6042655.794670] [<ffffffff805c6551>] ip_rcv_finish+0x191/0x330
> [6042655.794672] [<ffffffff805c6936>] ip_rcv+0x246/0x2e0
> [6042655.794676] [<ffffffff804d8e74>] e1000_clean_rx_irq+0x114/0x3a0
> [6042655.794678] [<ffffffff804dad70>] e1000_clean+0x180/0x2d0
> [6042655.794681] [<ffffffff8059f5a7>] net_rx_action+0x87/0x130
> [6042655.794683] [<ffffffff80259cd3>] __do_softirq+0x93/0x160
> [6042655.794687] [<ffffffff8022c9fc>] call_softirq+0x1c/0x30
> [6042655.794689] [<ffffffff8022e455>] do_softirq+0x35/0x80
> [6042655.794691] [<ffffffff8022e523>] do_IRQ+0x83/0x110
> [6042655.794693] [<ffffffff8022c2d3>] ret_from_intr+0x0/0xa
> [6042655.794694] <EOI> [<ffffffff80632190>] _spin_lock+0x10/0x20
> [6042655.794700] [<ffffffff802bb2fc>] d_find_alias+0x1c/0x40
> [6042655.794703] [<ffffffff802bd96d>] d_obtain_alias+0x4d/0x140
> [6042655.794706] [<ffffffff8033ffd3>] exportfs_decode_fh+0x63/0x2a0
> [6042655.794708] [<ffffffff80343970>] nfsd_acceptable+0x0/0x110
> [6042655.794711] [<ffffffff8061e74a>] cache_check+0x4a/0x4d0
> [6042655.794714] [<ffffffff80349437>] exp_find_key+0x57/0xe0
> [6042655.794717] [<ffffffff80592a35>] sock_recvmsg+0xd5/0x110
> [6042655.794719] [<ffffffff80349552>] exp_find+0x92/0xa0
> [6042655.794721] [<ffffffff80343e59>] fh_verify+0x369/0x680
> [6042655.794724] [<ffffffff8024add9>] check_preempt_wakeup+0xf9/0x120
> [6042655.794726] [<ffffffff803460be>] nfsd_open+0x2e/0x180
> [6042655.794728] [<ffffffff80346574>] nfsd_write+0xc4/0x120
> [6042655.794730] [<ffffffff8034dac0>] nfsd3_proc_write+0xb0/0x150
> [6042655.794732] [<ffffffff8034040a>] nfsd_dispatch+0xba/0x270
> [6042655.794736] [<ffffffff80615a1e>] svc_process+0x49e/0x800
> [6042655.794738] [<ffffffff8024dc80>] default_wake_function+0x0/0x10
> [6042655.794740] [<ffffffff80631fd7>] __down_read+0x17/0xae
> [6042655.794742] [<ffffffff80340b79>] nfsd+0x199/0x2b0
> [6042655.794743] [<ffffffff803409e0>] nfsd+0x0/0x2b0
> [6042655.794747] [<ffffffff802691d7>] kthread+0x47/0x90
> [6042655.794749] [<ffffffff8022c8fa>] child_rip+0xa/0x20
> [6042655.794751] [<ffffffff80269190>] kthread+0x0/0x90
> [6042655.794753] [<ffffffff8022c8f0>] child_rip+0x0/0x20
> [6042655.794754] Mem-Info:
...
> [6042655.794776] Active_anon:108072 active_file:103321 inactive_anon:31621
> [6042655.794777] inactive_file:984722 unevictable:0 dirty:71104 writeback:0
> unstable:0
> [6042655.794778] free:8659 slab:746182 mapped:8842 pagetables:5374 bounce:0
> [6042655.794780] DMA free:9736kB min:16kB low:20kB high:24kB active_anon:0kB
> inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB
> present:8744kB pages_scanned:0 all_unreclaimable? yes
> [6042655.794783] lowmem_reserve[]: 0 3246 7980 7980

ZONE_DMA is inaccessible because of lowmem_reserve, assuming you have 4K
pages: 9736K free < (16K min + (7980 pages * 4K /page)).

> [6042655.794787] DMA32 free:21420kB min:6656kB low:8320kB high:9984kB
> active_anon:52420kB inactive_anon:38552kB active_file:146252kB
> inactive_file:1651512kB unevictable:0kB present:3324312kB pages_scanned:0
> all_unreclaimable? no
> [6042655.794789] lowmem_reserve[]: 0 0 4734 4734

Likewise for ZONE_DMA32: 21420K free < (6656K min + (4734 pages *
4K/page)).

> [6042655.794793] Normal free:3480kB min:9708kB low:12132kB high:14560kB
> active_anon:379868kB inactive_anon:87932kB active_file:267032kB
> inactive_file:2287376kB unevictable:0kB present:4848000kB pages_scanned:0
> all_unreclaimable? no
> [6042655.794795] lowmem_reserve[]: 0 0 0 0

And ZONE_NORMAL is oom: 3480K free < 9708K min.


ipv4: don't warn about skb ack allocation failures

tcp_send_ack() will recover from alloc_skb() allocation failures, so avoid
emitting warnings.

Signed-off-by: David Rientjes <rientjes@google.com>
---
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2442,7 +2442,7 @@ void tcp_send_ack(struct sock *sk)
* tcp_transmit_skb() will set the ownership to this
* sock.
*/
- buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
+ buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC | __GFP_NOWARN);
if (buff == NULL) {
inet_csk_schedule_ack(sk);
inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;

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