linux-kernel - Re: [RESEND RFC PATCH v2 1/1] mm/vmalloc.c: simplify /proc/vmallocinfo implementation

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Date:   Wed, 12 Oct 2016 11:25:18 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     zijun_hu <zijun_hu@...o.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, rientjes@...gle.com,
        tj@...nel.org, mingo@...nel.org, iamjoonsoo.kim@....com,
        mgorman@...hsingularity.net, sfr@...b.auug.org.au,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, zijun_hu@....com
Subject: Re: [RESEND RFC PATCH v2 1/1] mm/vmalloc.c: simplify
 /proc/vmallocinfo implementation

On Wed 12-10-16 16:23:01, zijun_hu wrote:
> From: zijun_hu <zijun_hu@....com>
> 
> many seq_file helpers exist for simplifying implementation of virtual files
> especially, for /proc nodes. however, the helpers for iteration over
> list_head are available but aren't adopted to implement /proc/vmallocinfo
> currently.
> 
> simplify /proc/vmallocinfo implementation by existing seq_file helpers

the simplification is nice and code duplication removal useful

> Signed-off-by: zijun_hu <zijun_hu@....com>

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

Thanks!

> ---
>  Changes in v2:
>   - the redundant type cast is removed as advised by rientjes@...gle.com
>   - commit messages are updated
> 
>  mm/vmalloc.c | 27 +++++----------------------
>  1 file changed, 5 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index f2481cb4e6b2..e73948afac70 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2574,32 +2574,13 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  static void *s_start(struct seq_file *m, loff_t *pos)
>  	__acquires(&vmap_area_lock)
>  {
> -	loff_t n = *pos;
> -	struct vmap_area *va;
> -
>  	spin_lock(&vmap_area_lock);
> -	va = list_first_entry(&vmap_area_list, typeof(*va), list);
> -	while (n > 0 && &va->list != &vmap_area_list) {
> -		n--;
> -		va = list_next_entry(va, list);
> -	}
> -	if (!n && &va->list != &vmap_area_list)
> -		return va;
> -
> -	return NULL;
> -
> +	return seq_list_start(&vmap_area_list, *pos);
>  }
>  
>  static void *s_next(struct seq_file *m, void *p, loff_t *pos)
>  {
> -	struct vmap_area *va = p, *next;
> -
> -	++*pos;
> -	next = list_next_entry(va, list);
> -	if (&next->list != &vmap_area_list)
> -		return next;
> -
> -	return NULL;
> +	return seq_list_next(p, &vmap_area_list, pos);
>  }
>  
>  static void s_stop(struct seq_file *m, void *p)
> @@ -2634,9 +2615,11 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
>  
>  static int s_show(struct seq_file *m, void *p)
>  {
> -	struct vmap_area *va = p;
> +	struct vmap_area *va;
>  	struct vm_struct *v;
>  
> +	va = list_entry(p, struct vmap_area, list);
> +
>  	/*
>  	 * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
>  	 * behalf of vmap area is being tear down or vm_map_ram allocation.
> -- 
> 1.9.1
> 
> --
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-- 
Michal Hocko
SUSE Labs