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

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Date:	Wed, 28 Mar 2007 15:26:56 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org,
	William Lee Irwin III <wli@...omorphy.com>,
	akpm@...ux-foundation.org, jeremy@...p.org, zach@...are.com
Subject: Re: [RFC] i386: Remove page sized slabs for pgds and pmds

* 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)

I must've glazed over something, I thought this was removal of slabs?

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.

> +static struct kmem_cache *pgd_cache;
> +
> +void __init pgtable_cache_init(void)
> +{
> +	pgd_cache = kmem_cache_create("pgd",
> +				PTRS_PER_PGD*sizeof(pgd_t),
> +				PTRS_PER_PGD*sizeof(pgd_t),
> +				SLAB_PANIC,
> +				NULL,
> +				NULL);
> +}
> +#else /* !CONFIG_HIGHMEM64G */
> +#define __pgd_alloc()		((pgd_t *)get_zeroed_page(GFP_KERNEL|__GFP_REPEAT))
> +#define __pgd_free(pgd)		free_page((unsigned long)(pgd))
> +#endif /* !CONFIG_HIGHMEM64G */
>  
>  pgd_t *pgd_alloc(struct mm_struct *mm)
>  {
>  	int i;
> -	pgd_t *pgd = kmem_cache_alloc(pgd_cache, GFP_KERNEL);
> +	pgd_t *pgd = __pgd_alloc();
>  
> -	if (PTRS_PER_PMD == 1 || !pgd)
> +	if (!pgd)
> +		return NULL;
> +	memcpy(&pgd[USER_PTRS_PER_PGD], &swapper_pg_dir[USER_PTRS_PER_PGD],
> +						KERNEL_PGD_PTRS*sizeof(pgd_t));

clone_pgd_range() for consistency?  and it seems we lost a paravirt_alloc_pd_clone()
in there somewhere.

> +	if (PTRS_PER_PMD == 1)
>  		return pgd;
-
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