Re: [PATCH v3 4/4] mm: Remove managed_page_count spinlock

[Michal Hocko]

On Thu 08-11-18 13:53:18, Arun KS wrote:
> Now totalram_pages and managed_pages are atomic varibles. No need
> of managed_page_count spinlock.

As explained earlier. Please add a motivation here. Feel free to reuse
wording from http://lkml.kernel.org/r/20181107103630.GF2453@xxxxxxxxxxxxxx

> 
> Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
> Reviewed-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  include/linux/mmzone.h | 6 ------
>  mm/page_alloc.c        | 5 -----
>  2 files changed, 11 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index e73dc31..c71b4d9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -428,12 +428,6 @@ struct zone {
>  	 * Write access to present_pages at runtime should be protected by
>  	 * mem_hotplug_begin/end(). Any reader who can't tolerant drift of
>  	 * present_pages should get_online_mems() to get a stable value.
> -	 *
> -	 * Read access to managed_pages should be safe because it's unsigned
> -	 * long. Write access to zone->managed_pages and totalram_pages are
> -	 * protected by managed_page_count_lock at runtime. Idealy only
> -	 * adjust_managed_page_count() should be used instead of directly
> -	 * touching zone->managed_pages and totalram_pages.
>  	 */
>  	atomic_long_t		managed_pages;
>  	unsigned long		spanned_pages;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f8b64cc..26c5e14 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -122,9 +122,6 @@
>  };
>  EXPORT_SYMBOL(node_states);
>  
> -/* Protect totalram_pages and zone->managed_pages */
> -static DEFINE_SPINLOCK(managed_page_count_lock);
> -
>  atomic_long_t _totalram_pages __read_mostly;
>  EXPORT_SYMBOL(_totalram_pages);
>  unsigned long totalreserve_pages __read_mostly;
> @@ -7065,14 +7062,12 @@ static int __init cmdline_parse_movablecore(char *p)
>  
>  void adjust_managed_page_count(struct page *page, long count)
>  {
> -	spin_lock(&managed_page_count_lock);
>  	atomic_long_add(count, &page_zone(page)->managed_pages);
>  	totalram_pages_add(count);
>  #ifdef CONFIG_HIGHMEM
>  	if (PageHighMem(page))
>  		totalhigh_pages_add(count);
>  #endif
> -	spin_unlock(&managed_page_count_lock);
>  }
>  EXPORT_SYMBOL(adjust_managed_page_count);
>  
> -- 
> 1.9.1

-- 
Michal Hocko
SUSE Labs