Re: [PATCHv4 02/10] mm: convert mm->nr_ptes to atomic_t

[Cody P Schafer <cody@linux.vnet.ibm.com>]

On 09/27/2013 06:16 AM, Kirill A. Shutemov wrote:
> With split page table lock for PMD level we can't hold
> mm->page_table_lock while updating nr_ptes.
>
> Let's convert it to atomic_t to avoid races.
>

> ---

> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 84e0c56e1e..99f19e850d 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -339,6 +339,7 @@ struct mm_struct {
>   	pgd_t * pgd;
>   	atomic_t mm_users;			/* How many users with user space? */
>   	atomic_t mm_count;			/* How many references to "struct mm_struct" (users count as 1) */
> +	atomic_t nr_ptes;			/* Page table pages */
>   	int map_count;				/* number of VMAs */
>
>   	spinlock_t page_table_lock;		/* Protects page tables and some counters */
> @@ -360,7 +361,6 @@ struct mm_struct {
>   	unsigned long exec_vm;		/* VM_EXEC & ~VM_WRITE */
>   	unsigned long stack_vm;		/* VM_GROWSUP/DOWN */
>   	unsigned long def_flags;
> -	unsigned long nr_ptes;		/* Page table pages */
>   	unsigned long start_code, end_code, start_data, end_data;
>   	unsigned long start_brk, brk, start_stack;
>   	unsigned long arg_start, arg_end, env_start, env_end;

Will 32bits always be enough here? Should atomic_long_t be used instead?