netdev - Re: [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC reserves

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Message-ID: <20110428161933.1f1266e6@notabene.brown>
Date:	Thu, 28 Apr 2011 16:19:33 +1000
From:	NeilBrown <neilb@...e.de>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC
 reserves

On Wed, 27 Apr 2011 17:08:06 +0100 Mel Gorman <mgorman@...e.de> wrote:


> @@ -1578,7 +1589,7 @@ static inline struct sk_buff *netdev_alloc_skb_ip_align(struct net_device *dev,
>   */
>  static inline struct page *__netdev_alloc_page(struct net_device *dev, gfp_t gfp_mask)
>  {
> -	return alloc_pages_node(NUMA_NO_NODE, gfp_mask, 0);
> +	return alloc_pages_node(NUMA_NO_NODE, gfp_mask | __GFP_MEMALLOC, 0);
>  }
>  

I'm puzzling a bit over this change.
__netdev_alloc_page appears to be used to get pages to put in ring buffer
for a network card to DMA received packets into.  So it is OK to use
__GFP_MEMALLOC for these allocations providing we mark the resulting skb as
'pfmemalloc' if a reserved page was used.

However I don't see where that marking is done.
I think it should be in skb_fill_page_desc, something like:

  if (page->pfmemalloc)
	skb->pfmemalloc = true;

Is this covered somewhere else that I am missing?

Thanks,
NeilBrown

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