linux-kernel - Re: [PATCHv2 2/2] xtensa: use buddy allocator for PTE table

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Message-ID: <CAMo8Bf+oo4WCE366+bPoD5Y=Q3pCF0NVnfjXVqz8=nZ45_XY7Q@mail.gmail.com>
Date:	Mon, 14 Oct 2013 19:19:07 +0400
From:	Max Filippov <jcmvbkbc@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Chris Zankel <chris@...kel.net>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>
Subject: Re: [PATCHv2 2/2] xtensa: use buddy allocator for PTE table

On Mon, Oct 14, 2013 at 6:32 PM, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
> At the moment xtensa uses slab allocator for PTE table. It doesn't work
> with enabled split page table lock: slab uses page->slab_cache and
> page->first_page for its pages. These fields share stroage with
> page->ptl.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Chris Zankel <chris@...kel.net>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> ---
> v2:
>  - add missed return in pte_alloc_one_kernel;
>
>  arch/xtensa/include/asm/pgalloc.h | 20 ++++++++++++--------
>  arch/xtensa/include/asm/pgtable.h |  3 +--
>  arch/xtensa/mm/mmu.c              | 20 --------------------
>  3 files changed, 13 insertions(+), 30 deletions(-)
>
> diff --git a/arch/xtensa/include/asm/pgalloc.h b/arch/xtensa/include/asm/pgalloc.h
> index b8774f1e21..8507b32d6e 100644
> --- a/arch/xtensa/include/asm/pgalloc.h
> +++ b/arch/xtensa/include/asm/pgalloc.h
> @@ -38,14 +38,18 @@ static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
>         free_page((unsigned long)pgd);
>  }
>
> -/* Use a slab cache for the pte pages (see also sparc64 implementation) */
> -
> -extern struct kmem_cache *pgtable_cache;
> -
>  static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm,
>                                          unsigned long address)
>  {
> -       return kmem_cache_alloc(pgtable_cache, GFP_KERNEL|__GFP_REPEAT);
> +       pte_t *ptep;
> +       int i;
> +
> +       ptep = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_REPEAT);
> +       if (!ptep)
> +               return NULL;
> +       for (i = 0; i < 1024; i++, ptep++)
> +               pte_clear(NULL, 0, ptep);
> +       return ptep;

You're returning modified ptep, not the allocated one.

>  }
>
>  static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
> @@ -59,7 +63,7 @@ static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
>                 return NULL;
>         page = virt_to_page(pte);
>         if (!pgtable_page_ctor(page)) {
> -               kmem_cache_free(pgtable_cache, pte);
> +               __free_page(page);
>                 return NULL;
>         }
>         return page;
> @@ -67,13 +71,13 @@ static inline pgtable_t pte_alloc_one(struct mm_struct *mm,
>
>  static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
>  {
> -       kmem_cache_free(pgtable_cache, pte);
> +       free_page((unsigned long)pte);
>  }
>
>  static inline void pte_free(struct mm_struct *mm, pgtable_t pte)
>  {
>         pgtable_page_dtor(pte);
> -       kmem_cache_free(pgtable_cache, page_address(pte));
> +       __free_page(pte);
>  }
>  #define pmd_pgtable(pmd) pmd_page(pmd)
>
> diff --git a/arch/xtensa/include/asm/pgtable.h b/arch/xtensa/include/asm/pgtable.h
> index 0fdf5d043f..216446295a 100644
> --- a/arch/xtensa/include/asm/pgtable.h
> +++ b/arch/xtensa/include/asm/pgtable.h
> @@ -220,12 +220,11 @@ extern unsigned long empty_zero_page[1024];
>  #ifdef CONFIG_MMU
>  extern pgd_t swapper_pg_dir[PAGE_SIZE/sizeof(pgd_t)];
>  extern void paging_init(void);
> -extern void pgtable_cache_init(void);
>  #else
>  # define swapper_pg_dir NULL
>  static inline void paging_init(void) { }
> -static inline void pgtable_cache_init(void) { }
>  #endif
> +static inline void pgtable_cache_init(void) { }
>
>  /*
>   * The pmd contains the kernel virtual address of the pte page.
> diff --git a/arch/xtensa/mm/mmu.c b/arch/xtensa/mm/mmu.c
> index a1077570e3..c43771c974 100644
> --- a/arch/xtensa/mm/mmu.c
> +++ b/arch/xtensa/mm/mmu.c
> @@ -50,23 +50,3 @@ void __init init_mmu(void)
>          */
>         set_ptevaddr_register(PGTABLE_START);
>  }
> -
> -struct kmem_cache *pgtable_cache __read_mostly;
> -
> -static void pgd_ctor(void *addr)
> -{
> -       pte_t *ptep = (pte_t *)addr;
> -       int i;
> -
> -       for (i = 0; i < 1024; i++, ptep++)
> -               pte_clear(NULL, 0, ptep);
> -
> -}
> -
> -void __init pgtable_cache_init(void)
> -{
> -       pgtable_cache = kmem_cache_create("pgd",
> -                       PAGE_SIZE, PAGE_SIZE,
> -                       SLAB_HWCACHE_ALIGN,
> -                       pgd_ctor);
> -}
> --
> 1.8.4.rc3
>



-- 
Thanks.
-- Max
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