linux-kernel - Re: [PATCH] igb: don't reuse pages with pfmemalloc flag

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Date:	Wed, 22 Oct 2014 08:45:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Roman Gushchin <klamm@...dex-team.ru>
Cc:	jeffrey.t.kirsher@...el.com, jesse.brandeburg@...el.com,
	bruce.w.allan@...el.com, carolyn.wyborny@...el.com,
	donald.c.skidmore@...el.com, gregory.v.rose@...el.com,
	peter.p.waskiewicz.jr@...el.com, alexander.h.duyck@...el.com,
	john.ronciak@...el.com, tushar.n.dave@...el.com,
	davem@...emloft.net, sassmann@...nic.de,
	gregkh@...uxfoundation.org, e1000-devel@...ts.sourceforge.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] igb: don't reuse pages with pfmemalloc flag

On Wed, 2014-10-22 at 17:50 +0400, Roman Gushchin wrote:
> Incoming packet is dropped silently by sk_filter(), if the skb was
> allocated from pfmemalloc reserves and the corresponding socket is
> not marked with the SOCK_MEMALLOC flag.
> 
> Igb driver allocates pages for DMA with __skb_alloc_page(), which
> calls alloc_pages_node() with the __GFP_MEMALLOC flag. So, in case
> of OOM condition, igb can get pages with pfmemalloc flag set.
> 
> If an incoming packet hits the pfmemalloc page and is large enough
> (small packets are copying into the memory, allocated with
> netdev_alloc_skb_ip_align(), so they are not affected), it will be
> dropped.
> 
> This behavior is ok under high memory pressure, but the problem is
> that the igb driver reuses these mapped pages. So, packets are still
> dropping even if all memory issues are gone and there is a plenty
> of free memory.
> 
> In my case, some TCP sessions hang on a small percentage (< 0.1%)
> of machines days after OOMs.
> 
> Fix this by avoiding reuse of such pages.
> 
> Signed-off-by: Roman Gushchin <klamm@...dex-team.ru>
> ---

Interesting...

It seems we also need to clear skb->pfmemalloc in napi_reuse_skb()



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