linux-kernel - Re: [PATCH 1/1] mm/vmalloc: convert vmap_lazy_nr to atomic_long

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Message-ID: <20190201124528.GN11599@dhcp22.suse.cz>
Date:   Fri, 1 Feb 2019 13:45:28 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/1] mm/vmalloc: convert vmap_lazy_nr to atomic_long_t

On Thu 31-01-19 17:24:52, Uladzislau Rezki (Sony) wrote:
> vmap_lazy_nr variable has atomic_t type that is 4 bytes integer
> value on both 32 and 64 bit systems. lazy_max_pages() deals with
> "unsigned long" that is 8 bytes on 64 bit system, thus vmap_lazy_nr
> should be 8 bytes on 64 bit as well.

But do we really need 64b number of _pages_? I have hard time imagine
that we would have that many lazy pages to accumulate.

> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index abe83f885069..755b02983d8d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -632,7 +632,7 @@ static unsigned long lazy_max_pages(void)
>  	return log * (32UL * 1024 * 1024 / PAGE_SIZE);
>  }
>  
> -static atomic_t vmap_lazy_nr = ATOMIC_INIT(0);
> +static atomic_long_t vmap_lazy_nr = ATOMIC_LONG_INIT(0);
>  
>  /*
>   * Serialize vmap purging.  There is no actual criticial section protected
> @@ -650,7 +650,7 @@ static void purge_fragmented_blocks_allcpus(void);
>   */
>  void set_iounmap_nonlazy(void)
>  {
> -	atomic_set(&vmap_lazy_nr, lazy_max_pages()+1);
> +	atomic_long_set(&vmap_lazy_nr, lazy_max_pages()+1);
>  }
>  
>  /*
> @@ -658,10 +658,10 @@ void set_iounmap_nonlazy(void)
>   */
>  static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
>  {
> +	unsigned long resched_threshold;
>  	struct llist_node *valist;
>  	struct vmap_area *va;
>  	struct vmap_area *n_va;
> -	int resched_threshold;
>  
>  	lockdep_assert_held(&vmap_purge_lock);
>  
> @@ -681,16 +681,16 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
>  	}
>  
>  	flush_tlb_kernel_range(start, end);
> -	resched_threshold = (int) lazy_max_pages() << 1;
> +	resched_threshold = lazy_max_pages() << 1;
>  
>  	spin_lock(&vmap_area_lock);
>  	llist_for_each_entry_safe(va, n_va, valist, purge_list) {
> -		int nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
> +		unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
>  
>  		__free_vmap_area(va);
> -		atomic_sub(nr, &vmap_lazy_nr);
> +		atomic_long_sub(nr, &vmap_lazy_nr);
>  
> -		if (atomic_read(&vmap_lazy_nr) < resched_threshold)
> +		if (atomic_long_read(&vmap_lazy_nr) < resched_threshold)
>  			cond_resched_lock(&vmap_area_lock);
>  	}
>  	spin_unlock(&vmap_area_lock);
> @@ -727,10 +727,10 @@ static void purge_vmap_area_lazy(void)
>   */
>  static void free_vmap_area_noflush(struct vmap_area *va)
>  {
> -	int nr_lazy;
> +	unsigned long nr_lazy;
>  
> -	nr_lazy = atomic_add_return((va->va_end - va->va_start) >> PAGE_SHIFT,
> -				    &vmap_lazy_nr);
> +	nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
> +				PAGE_SHIFT, &vmap_lazy_nr);
>  
>  	/* After this point, we may free va at any time */
>  	llist_add(&va->purge_list, &vmap_purge_list);
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs