linux-kernel - Re: [PATCH] Containment measures for slab objects on scatter gather lists

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Message-ID: <Pine.LNX.4.64.0706282119330.11676@schroedinger.engr.sgi.com>
Date:	Thu, 28 Jun 2007 21:22:22 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	David Miller <davem@...emloft.net>
cc:	hugh@...itas.com, James.Bottomley@...eleye.com,
	rmk+lkml@....linux.org.uk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Containment measures for slab objects on scatter gather
 lists

On Thu, 28 Jun 2007, David Miller wrote:

> > Still a better solution would be to not use the slab allocator at all for 
> > the objects that are used to send commands to the devices. These are not 
> > permanent and grabbing a page from the pcp lists and putting it back is 
> > likely as fast as performing a kmalloc.
> 
> Jens Axboe wants to get references to the page structs behind
> kmalloc() allocated pages in his networking splice work.

You can get such a reference and then the slab page will be in limbo if 
all objects are freed until that reference is given up. The reference 
method is also use by kmem_cache_vacate() (but that is slab internal).

> We could make a special allocator in the networking that carves
> chunks out of pages but I'm sure you'll find that about as stupid
> and wasteful as I do :-)

Well then I guess this containment patch is as good as we can get.
It makes sure that things do not get out of hand.

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