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

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Message-Id: <20071004103830.6A6A.Y-GOTO@jp.fujitsu.com>
Date:	Thu, 04 Oct 2007 11:00:12 +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 Wed, 3 Oct 2007, Yasunori Goto wrote:
> 
> > > 
> > > 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?
> 
> The slab for which you are trying to set the kmem_cache_node pointer to 
> NULL needs to be shrunk.
>  
> > 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.
> 
> Hmmm.. Ok for cpu hotplug you could simply disregard the per cpu 
> structure if the per cpu slab was flushed first.
> 
> However, the per node structure may hold slabs with no objects even after 
> all objects were removed on a node. These need to be flushed by calling
> kmem_cache_shrink() on the slab cache.
> 
> On the other hand: If you can guarantee that they will not be used and 
> that no objects are in them and that you can recover the pages used in 
> different ways then zapping the per node pointer like that is okay.

Thanks for your advise. I'll reconsider and fix my patches.

Bye.

-- 
Yasunori Goto 


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