linux-kernel - Re: [PATCH] mm: remove pte_lock

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Date:   Thu, 29 Nov 2018 09:39:03 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Keith Busch <keith.busch@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove pte_lock_deinit()

On Wed 28-11-18 16:55:25, Yu Zhao wrote:
> Pagetable page doesn't touch page->mapping or have any used field
> that overlaps with it. No need to clear mapping in dtor. In fact,
> doing so might mask problems that otherwise would be detected by
> bad_page().

yes the layour of the structure has changed since Hugh introduced the
pte lock split

> Signed-off-by: Yu Zhao <yuzhao@...gle.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  include/linux/mm.h | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5411de93a363..7c8f4fc9244e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1900,13 +1900,6 @@ static inline bool ptlock_init(struct page *page)
>  	return true;
>  }
>  
> -/* Reset page->mapping so free_pages_check won't complain. */
> -static inline void pte_lock_deinit(struct page *page)
> -{
> -	page->mapping = NULL;
> -	ptlock_free(page);
> -}
> -
>  #else	/* !USE_SPLIT_PTE_PTLOCKS */
>  /*
>   * We use mm->page_table_lock to guard all pagetable pages of the mm.
> @@ -1917,7 +1910,7 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
>  }
>  static inline void ptlock_cache_init(void) {}
>  static inline bool ptlock_init(struct page *page) { return true; }
> -static inline void pte_lock_deinit(struct page *page) {}
> +static inline void ptlock_free(struct page *page) {}
>  #endif /* USE_SPLIT_PTE_PTLOCKS */
>  
>  static inline void pgtable_init(void)
> @@ -1937,7 +1930,7 @@ static inline bool pgtable_page_ctor(struct page *page)
>  
>  static inline void pgtable_page_dtor(struct page *page)
>  {
> -	pte_lock_deinit(page);
> +	ptlock_free(page);
>  	__ClearPageTable(page);
>  	dec_zone_page_state(page, NR_PAGETABLE);
>  }
> -- 
> 2.20.0.rc1.387.gf8505762e3-goog
> 

-- 
Michal Hocko
SUSE Labs