netdev - Re: [PATCH] net: use __GFP_NORETRY for high order allocations

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Message-ID: <alpine.DEB.2.02.1402061302020.9567@chino.kir.corp.google.com>
Date:	Thu, 6 Feb 2014 13:03:03 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Joe Perches <joe@...ches.com>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: use __GFP_NORETRY for high order allocations

On Thu, 6 Feb 2014, Joe Perches wrote:

> On Thu, 2014-02-06 at 10:42 -0800, Eric Dumazet wrote:
> > 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.
> []
> > 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
> []
> > diff --git 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;
> 
> Perhaps add __GFP_THISNODE too ?
> 

How does __GFP_THISNODE have anything to do with avoiding oom killing due 
to high-order fragmentation?  If they absolutely require local memory to 
currnet's cpu node then that would make sense, but the fallback still 
allocates order-0 memory remotely and with __GFP_THISNODE on this attempt 
we wouldn't even attempt remote reclaim.
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