linux-kernel - Re: [PATCH 4/4] mm: clarify mm_struct.mm

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Date:   Mon, 19 Dec 2016 14:15:56 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vegard Nossum <vegard.nossum@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] mm: clarify mm_struct.mm_{users,count} documentation

On Sun 18-12-16 13:32:29, Vegard Nossum wrote:
> Clarify documentation relating to mm_users and mm_count, and switch to
> kernel-doc syntax.

Looks good to me.
 
> Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>

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

> ---
>  include/linux/mm_types.h | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 08d947fc4c59..316c3e1fc226 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -407,8 +407,27 @@ struct mm_struct {
>  	unsigned long task_size;		/* size of task vm space */
>  	unsigned long highest_vm_end;		/* highest vma end address */
>  	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) */
> +
> +	/**
> +	 * @mm_users: The number of users including userspace.
> +	 *
> +	 * Use mmget()/mmget_not_zero()/mmput() to modify. When this drops
> +	 * to 0 (i.e. when the task exits and there are no other temporary
> +	 * reference holders), we also release a reference on @mm_count
> +	 * (which may then free the &struct mm_struct if @mm_count also
> +	 * drops to 0).
> +	 */
> +	atomic_t mm_users;
> +
> +	/**
> +	 * @mm_count: The number of references to &struct mm_struct
> +	 * (@mm_users count as 1).
> +	 *
> +	 * Use mmgrab()/mmdrop() to modify. When this drops to 0, the
> +	 * &struct mm_struct is freed.
> +	 */
> +	atomic_t mm_count;
> +
>  	atomic_long_t nr_ptes;			/* PTE page table pages */
>  #if CONFIG_PGTABLE_LEVELS > 2
>  	atomic_long_t nr_pmds;			/* PMD page table pages */
> -- 
> 2.11.0.1.gaa10c3f
> 

-- 
Michal Hocko
SUSE Labs