netdev - Re: [PATCH 09/13] netvm: Set PF_MEMALLOC as appropriate during SKB processing

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Date:	Tue, 26 Apr 2011 22:21:57 +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 09/13] netvm: Set PF_MEMALLOC as appropriate during SKB
 processing

On Tue, 26 Apr 2011 08:36:50 +0100 Mel Gorman <mgorman@...e.de> wrote:

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 3871bf6..2d79a20 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3095,6 +3095,27 @@ static void vlan_on_bond_hook(struct sk_buff *skb)
>  	}
>  }
>  
> +/*
> + * Limit which protocols can use the PFMEMALLOC reserves to those that are
> + * expected to be used for communication with swap.
> + */
> +static bool skb_pfmemalloc_protocol(struct sk_buff *skb)
> +{
> +	if (skb_pfmemalloc(skb))
> +		switch (skb->protocol) {
> +		case __constant_htons(ETH_P_ARP):
> +		case __constant_htons(ETH_P_IP):
> +		case __constant_htons(ETH_P_IPV6):
> +		case __constant_htons(ETH_P_8021Q):
> +			break;
> +
> +		default:
> +			return false;
> +		}
> +
> +	return true;
> +}

This sort of thing really bugs me :-)
Neither the comment nor the function name actually describe what the function
is doing.  The function is checking *2* things.
   is_pfmemalloc_skb_or_pfmemalloc_protocol()
might be a more correct name, but is too verbose.

I would prefer the skb_pfmemalloc test were removed from here and ....

> +	if (!skb_pfmemalloc_protocol(skb))
> +		goto drop;
> +

...added here so this becomes:

      if (!skb_pfmemalloc(skb) && !skb_pfmemalloc_protocol(skb))
                goto drop;

which actually makes sense.

Thanks,
NeilBrown

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