On Tue, Apr 26, 2011 at 10:21:57PM +1000, NeilBrown wrote:
> On Tue, 26 Apr 2011 08:36:50 +0100 Mel Gorman <mgorman@xxxxxxx> 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.
>
Moving the check is neater but that check should be
if (skb_pfmemalloc(skb) && !skb_pfmemalloc_protocol(skb))
? It's only if the skb was allocated from emergency reserves that we
need to consider dropping it to make way for other packets to be
received.
--
Mel Gorman
SUSE Labs
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