netdev - Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash table

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Message-ID: <20130314123448.GA27559@order.stressinduktion.org>
Date:	Thu, 14 Mar 2013 13:34:48 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	yoshfuji@...ux-ipv6.org, brouer@...hat.com
Subject: Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash table

On Thu, Mar 14, 2013 at 09:47:24AM -0000, David Laight wrote:
> > On Wed, Mar 13, 2013 at 09:36:52PM -0700, Stephen Hemminger wrote:
> > > > +#define INET_FRAG_FIND_CHECK(val)                                      \
> > > > +       ({                                                              \
> > > > +               static const char ___mem[] =                            \
> > > > +                       KERN_ERR pr_fmt(                                \
> > > > +                               "inet_frag_find: No memory left."       \
> > > > +                               " Dropping fragment.\n");               \
> > > > +               static const char ___limit[] =                          \
> > > > +                       KERN_WARNING pr_fmt(                            \
> > > > +                               "inet_frag_find: Fragment hash bucket"  \
> > > > +                               " list length grew above limit "        \
> > > > +                               __stringify(INETFRAGS_MAXDEPTH)         \
> > > > +                               ". Dropping fragment.\n");              \
> > > > +               bool ___b = true;                                       \
> > > > +               if (IS_ERR_OR_NULL(val)) {                              \
> > > > +                       ___b = false;                                   \
> > > > +                       if (PTR_ERR(val) == -ENOBUFS)                   \
> > > > +                               LIMIT_NETDEBUG(___limit);               \
> > > > +                       else                                            \
> > > > +                               LIMIT_NETDEBUG(___mem);                 \
> > > > +               }                                                       \
> > > > +               ___b;                                                   \
> > > > +       })
> > > > +
> > >
> > > Big macros suck, write it as an inline function or better yet a real function.
> > 
> > I switched to the macro to have string expansion with pr_fmt. So it is visible
> > from the dmesg if IPv4, IPv6 or IPv6-nf did generate the message. This could
> > be done with a function, too, but would require a bit more string handling.
> 
> I'd guess it would be best to have the IS_ERR_OR_NULL() inline calling a
> real function on error.

I'll explore later on how to achieve this. My rational was to
not do dynamic string handling to build the error messages. Perhaps I
can achieve both at the same time. :)

> I'd also have thought that INETFRAGS_MAXDEPTH should be run-time tunable.

128 is actually a pretty high limit. Have you seen the patch I posted before
this one? I tried to come up with a solution to dynamically calculate
max_depth based on the max_thresh of the fragmentation cache. What do you
think about that solution?

Thanks!

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