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Date:	Thu, 06 Feb 2014 18:03:23 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: use __GFP_NORETRY for high order allocations

Eric Dumazet <eric.dumazet@...il.com> writes:

> From: Eric Dumazet <edumazet@...gle.com>
>
> sock_alloc_send_pskb() & sk_page_frag_refill()
> have a loop trying high order allocations to prepare
> skb with low number of fragments as this increases performance.
>
> Problem is that under memory pressure/fragmentation, this can
> trigger OOM while the intent was only to try the high order
> allocations, then fallback to order-0 allocations.
>
> We had various reports from unexpected regressions.
>
> According to David, setting __GFP_NORETRY should be fine,
> as the asynchronous compaction is still enabled, and this
> will prevent OOM from kicking as in :
>
> CFSClientEventm invoked oom-killer: gfp_mask=0x42d0, order=3, oom_adj=0,
> oom_score_adj=0, oom_score_badness=2 (enabled),memcg_scoring=disabled
> CFSClientEventm 
>
> Call Trace:
>  [<ffffffff8043766c>] dump_header+0xe1/0x23e
>  [<ffffffff80437a02>] oom_kill_process+0x6a/0x323
>  [<ffffffff80438443>] out_of_memory+0x4b3/0x50d
>  [<ffffffff8043a4a6>] __alloc_pages_may_oom+0xa2/0xc7
>  [<ffffffff80236f42>] __alloc_pages_nodemask+0x1002/0x17f0
>  [<ffffffff8024bd23>] alloc_pages_current+0x103/0x2b0
>  [<ffffffff8028567f>] sk_page_frag_refill+0x8f/0x160
>  [<ffffffff80295fa0>] tcp_sendmsg+0x560/0xee0
>  [<ffffffff802a5037>] inet_sendmsg+0x67/0x100
>  [<ffffffff80283c9c>] __sock_sendmsg_nosec+0x6c/0x90
>  [<ffffffff80283e85>] sock_sendmsg+0xc5/0xf0
>  [<ffffffff802847b6>] __sys_sendmsg+0x136/0x430
>  [<ffffffff80284ec8>] sys_sendmsg+0x88/0x110
>  [<ffffffff80711472>] system_call_fastpath+0x16/0x1b
> Out of Memory: Kill process 2856 (bash) score 9999 or sacrifice child
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: David Rientjes <rientjes@...gle.com>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

I have seen similiar order 3 allocation failures as well and reached the
same conclusion that __GFP_NORETRY was the solution.

Eric
> ---
>  net/core/sock.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 0c127dcdf6a8..5b6a9431b017 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1775,7 +1775,9 @@ struct sk_buff *sock_alloc_send_pskb(struct sock *sk, unsigned long header_len,
>  			while (order) {
>  				if (npages >= 1 << order) {
>  					page = alloc_pages(sk->sk_allocation |
> -							   __GFP_COMP | __GFP_NOWARN,
> +							   __GFP_COMP |
> +							   __GFP_NOWARN |
> +							   __GFP_NORETRY,
>  							   order);
>  					if (page)
>  						goto fill_page;
> @@ -1845,7 +1847,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio)
>  		gfp_t gfp = prio;
>  
>  		if (order)
> -			gfp |= __GFP_COMP | __GFP_NOWARN;
> +			gfp |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY;
>  		pfrag->page = alloc_pages(gfp, order);
>  		if (likely(pfrag->page)) {
>  			pfrag->offset = 0;
>
>
> --
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