netdev - Re: [PATCH] slub: fix slab_pad

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Message-ID: <20090903150139.GC6761@linux.vnet.ibm.com>
Date:	Thu, 3 Sep 2009 08:01:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Patrick McHardy <kaber@...sh.net>, Robin Holt <holt@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesper Dangaard Brouer <hawk@...x.dk>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Netfilter Developers <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH] slub: fix slab_pad_check()

On Thu, Sep 03, 2009 at 01:38:50PM -0500, Christoph Lameter wrote:
> On Thu, 3 Sep 2009, Eric Dumazet wrote:
> 
> > Christoph Lameter a ?crit :
> > > On Thu, 3 Sep 2009, Eric Dumazet wrote:
> > >
> > >> on a SLAB_DESTROY_BY_RCU cache, there is no need to try to optimize this
> > >> rcu_barrier() call, unless we want superfast reboot/halt sequences...
> > >
> > > I stilll think that the action to quiesce rcu is something that the caller
> > > of kmem_cache_destroy must take care of.
> >
> > Do you mean :
> >
> > if (kmem_cache_shrink(s) == 0) {
> > 	rcu_barrier();
> > 	kmem_cache_destroy_no_rcu_barrier(s);
> > } else {
> > 	kmem_cache_destroy_with_rcu_barrier_because_SLAB_DESTROY_BY_RCU_cache(s);
> > }
> >
> > What would be the point ?
> 
> The above is port of slub?
> 
> I mean that (in this case) the net subsystem would have to deal with RCU quietness
> before disposing of the slab cache. There may be multiple ways of dealing
> with RCU. The RCU barrier may be unnecessary for future uses. Typically
> one would expect that all deferred handling of structures must be complete
> for correctness before disposing of the whole cache.

Which is precisely the point of the rcu_barrier(), right?

							Thanx, Paul

> > [PATCH] slub: fix slab_pad_check()
> 
> Acked-by: Christoph Lameter <cl@...ux-foundation.org>
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