netdev - Re: [PATCH 10/17] netvm: Allow skb allocation to use PFMEMALLOC reserves

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Message-ID: <20120621163029.GB6045@breakpoint.cc>
Date:	Thu, 21 Jun 2012 18:30:29 +0200
From:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Christie <michaelc@...wisc.edu>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH 10/17] netvm: Allow skb allocation to use PFMEMALLOC
 reserves

> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 1d6ecc8..9a58dcc 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -167,14 +206,19 @@ static void skb_under_panic(struct sk_buff *skb, int sz, void *here)
>   *	%GFP_ATOMIC.
>   */
>  struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
> -			    int fclone, int node)
> +			    int flags, int node)
>  {
>  	struct kmem_cache *cache;
>  	struct skb_shared_info *shinfo;
>  	struct sk_buff *skb;
>  	u8 *data;
> +	bool pfmemalloc;
>  
> -	cache = fclone ? skbuff_fclone_cache : skbuff_head_cache;
> +	cache = (flags & SKB_ALLOC_FCLONE)
> +		? skbuff_fclone_cache : skbuff_head_cache;
> +
> +	if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
> +		gfp_mask |= __GFP_MEMALLOC;
>  
>  	/* Get the HEAD */
>  	skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);

This is mostly used by nic to refil their RX skb pool. You add the
__GFP_MEMALLOC to the allocation to rise the change of a successfull refill
for the swap case.
A few drivers use build_skb() to create the skb. __netdev_alloc_skb()
shouldn't be affected since the allocation happens with GFP_ATOMIC. Looking at
TG3 it uses build_skb() and get_pages() / kmalloc(). Shouldn't this be some
considered?

Sebastian
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