netdev - Re: [PATCH 10/14] netvm: Set PF_MEMALLOC as appropriate during SKB processing

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Message-ID: <20110609125642.GS5247@suse.de>
Date:	Thu, 9 Jun 2011 13:56:42 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Micha? Miros?aw <mirqus@...il.com>
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>
Subject: Re: [PATCH 10/14] netvm: Set PF_MEMALLOC as appropriate during SKB
 processing

On Thu, Jun 09, 2011 at 02:28:24PM +0200, Micha? Miros?aw wrote:
> 2011/6/9 Mel Gorman <mgorman@...e.de>:
> > On Thu, Jun 09, 2011 at 12:21:31PM +0200, Micha? Miros?aw wrote:
> >> 2011/6/9 Mel Gorman <mgorman@...e.de>:
> >> [...]
> >> > +/*
> >> > + * 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)
> >> > +{
> >> > +       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):
> >> > +               return true;
> >> > +       default:
> >> > +               return false;
> >> > +       }
> >> > +}
> >>
> >> This is not needed and wrong. Whatever list there will be, it's going
> >> to always miss some obscure setup (or not that obscure, like
> >> ATAoverEthernet).
> >>
> >
> > NBD is updated in the series to set the socket information
> > appropriately but the same cannot be said of AoE. The necessary
> > changes have been made IPv4 and IPv6 to handle pfmemalloc sockets
> > but the same cannot be necessarily said for the other protocols. Yes,
> > the check could be removed but leaving it there makes a clear statement
> > on what scenario can be reasonably expected to work.
> 
> Ok. Then the comment before skb_pfmemalloc_protocol() is misleading.
> It should say that this is a list of protocols which implement the
> required special handling of PFMEMALLOC skbs.
> 

That's a very reasonable suggestion. My thinking behind that comment
was a backwards because I only "expected" protocols that implemented
the special handling to be used for swap :/

Thanks.

-- 
Mel Gorman
SUSE Labs
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