linux-kernel - Re: [RFC] i386: Remove page sized slabs for pgds and pmds

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Date:	Wed, 28 Mar 2007 15:45:39 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	Chris Wright <chrisw@...s-sol.org>,
	Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jeremy@...p.org, zach@...are.com
Subject: Re: [RFC] i386: Remove page sized slabs for pgds and pmds

* William Lee Irwin III (wli@...omorphy.com) wrote:
> * Christoph Lameter (clameter@....com) wrote:
> >> +#ifdef CONFIG_HIGHMEM64G
> >> +#define __pgd_alloc()		kmem_cache_alloc(pgd_cache, GFP_KERNEL|__GFP_REPEAT)
> >> +#define __pgd_free(pgd)		kmem_cache_free(pgd_cache, pgd)
> 
> On Wed, Mar 28, 2007 at 03:26:56PM -0700, Chris Wright wrote:
> > I must've glazed over something, I thought this was removal of slabs?
> 
> The pgd slab is not fully removable in the PAE case because a dedicated
> slab is the only way to enforce alignment for allocations as small as
> PAE PGD's.

Heh, yeah "page sized" is the part i glazed over, my fault.

> On Wed, Mar 28, 2007 at 03:26:56PM -0700, Chris Wright wrote:
> > BTW, this will interact shared_kernel_pmd patch that Jeremy's posted a
> > few times (I know at least wli has looked over that one).  We need to
> > make sure that PAE under at least Xen hypervisor has a page-sized pgd,
> > although the mmlist chaining looks nice to me.
> 
> That, not to mention the total lack of verification of the pageattr.c
> code, are among the reasons I didn't want it posted.
> 
> 
> * Christoph Lameter (clameter@....com) wrote:
> >> +	memcpy(&pgd[USER_PTRS_PER_PGD], &swapper_pg_dir[USER_PTRS_PER_PGD],
> >> +						KERNEL_PGD_PTRS*sizeof(pgd_t));
> 
> On Wed, Mar 28, 2007 at 03:26:56PM -0700, Chris Wright wrote:
> > clone_pgd_range() for consistency?  and it seems we lost a
> > paravirt_alloc_pd_clone() in there somewhere.
> 
> Yes, another reason why it shouldn't have been posted as-is. It was not
> intended to for anything more than comparative benchmarking on systems
> without graphics running on the bare metal as opposed to Xen/etc. guests.

OK, all good here.  Just wanted to make sure things didn't collide
too badly.

thanks,
-chris
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