linux-kernel - Re: [Patch / 002](memory hotplug) Callback function to create kmem_cache

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Message-Id: <20071003234201.B5F9.Y-GOTO@jp.fujitsu.com>
Date:	Wed, 03 Oct 2007 23:59:23 +0900
From:	Yasunori Goto <y-goto@...fujitsu.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...l.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [Patch / 002](memory hotplug) Callback function to create kmem_cache_node.

> On Tue, 2 Oct 2007, Yasunori Goto wrote:
> 
> > Do you mean that just nr_slabs should be checked like followings?
> > I'm not sure this is enough.
> > 
> >     :
> > if (s->node[nid]) {
> > 	n = get_node(s, nid);
> > 	if (!atomic_read(&n->nr_slabs)) {
> > 		s->node[nid] = NULL;
> > 		kmem_cache_free(kmalloc_caches, n);
> > 	}
> > }
> >     :
> >     :
> 
> That would work. But it would be better to shrink the cache first. The 
> first 2 slabs on a node may be empty and the shrinking will remove those. 
> If you do not shrink then the code may falsely assume that there are 
> objects on the node.

I'm sorry, but I don't think I understand what you mean... :-(
Could you explain more? 

Which slabs should be shrinked? kmem_cache_node and kmem_cache_cpu?

I think kmem_cache_cpu should be disabled by cpu hotplug,
not memory/node hotplug. Basically, cpu should be offlined before
memory offline on the node.

Sorry, I'm confusing now...

-- 
Yasunori Goto 


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