netdev - Re: [PATCH] ipvs: A couple of fixes and cleanups

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Date:	Mon, 11 Aug 2008 10:19:09 +0200 (CEST)
From:	Sven Wegener <sven.wegener@...aler.net>
To:	Simon Horman <horms@...ge.net.au>
cc:	wensong@...ux-vs.org, ja@....bg, netdev@...r.kernel.org,
	lvs-devel@...r.kernel.org
Subject: Re: [PATCH] ipvs: A couple of fixes and cleanups

On Mon, 11 Aug 2008, Simon Horman wrote:

> On Mon, Aug 11, 2008 at 08:43:54AM +0200, Sven Wegener wrote:
> > On Mon, 11 Aug 2008, Simon Horman wrote:
> > 
> > > On Sun, Aug 10, 2008 at 08:35:48PM +0200, Sven Wegener wrote:
> > > > On Sun, 10 Aug 2008, sven.wegener@...aler.net wrote:
> > > > 
> > > > > Hi guys,
> > > > > 
> > > > > here come a couple of fixes and cleanups for IPVS. Worth mentioning are the two
> > > > > possible deadlock fixes. One introduced by my last sync daemon work, which
> > > > > hasn't hit any stable kernel yet. The other one is in the estimator code and
> > > > > goes back to at leat since we started working with git for the kernel. The
> > > > > latter I think qualifies for -stable.
> > > > > 
> > > > > I've pushed the changes (8123b42..2e45552) based on davem's net tree here
> > > > > 
> > > > > 	git://git.stealer.net/linux-2.6.git stealer/ipvs/for-davem
> > > > 
> > > > I've included the register_ip_vs_protocol() annotation. Changes are now 
> > > > 8123b42..7ead17b. Diffstat has changed slightly, but is probably not worth 
> > > > posting again.
> > > 
> > > Hi Sven,
> > > 
> > > all these changes seem fine to me.
> > > 
> > > Acked-by: Simon Horman <horms@...ge.net.au>
> > > 
> > > With regards to ip_vs_zero_stats(), it uses
> > > 
> > >    memset(stats, 0, (char *)&stats->lock - (char *)stats);
> > > 
> > > to clear stats and then calls ip_vs_zero_estimator(), which uses
> > > 
> > >    est->last_conns = 0;
> > >    est->last_inpkts = 0;
> > >    ...
> > > 
> > > to clear stats->est.
> > > 
> > > I wonder if it would be cleaner to either clear
> > > stats->... directly in ip_vs_zero_stats(), or use
> > > memset in ip_vs_zero_estimator()?
> > 
> > Yeah, I wondered about the same. memset is probably simpler, but direct 
> > assignment makes it more obvious what is changed. Thinking about it, I'd 
> > prefer direct assignment, when not setting a complete structure to zero 
> > and there are not more than a handful lines needed to do it with direct 
> > assignment. But I'm fine with either way here. If we prefer the memset 
> > way, we should add a comment to both structures, saying that nobody should 
> > add anything non-statistic before the member we use to get the size.
> 
> To be honest I prefer direct assignment too. I think it is less fragile
> as the structures can be re-ordered without effecting how clear works.
> I'll post a (trivial) patch shortly.
> 
> > Also the estimator and statistics structures can be optimized to avoid 
> > some padding. I'll include these changes and resend.
> 
> Great.

Sadly the layout of the stats structure is shared with user space, so this 
can't be changed easily without breaking ABI.

Sven
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