Re: [PATCH v1 3/3] mm/shuffle: remove dynamic reconfiguration

[Michal Hocko]

[Add Dan]

On Tue 16-06-20 13:52:13, David Hildenbrand wrote:
> Commit e900a918b098 ("mm: shuffle initial free memory to improve
> memory-side-cache utilization") promised "autodetection of a
> memory-side-cache (to be added in a follow-on patch)" over a year ago.
> 
> The original series included patches [1], however, they were dropped
> during review [2] to be followed-up later.
> 
> Let's simplify for now and re-add when really (ever?) needed.
> 
> [1] https://lkml.kernel.org/r/154510700291.1941238.817190985966612531.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> [2] https://lkml.kernel.org/r/154690326478.676627.103843791978176914.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

While I am not against removing this unused code I am really curious
what is the future of the auto detection. Has this just fall through
cracks or there are some more serious problem to make detection
possible/reliable?

> ---
>  mm/shuffle.c | 28 ++--------------------------
>  mm/shuffle.h | 17 -----------------
>  2 files changed, 2 insertions(+), 43 deletions(-)
> 
> diff --git a/mm/shuffle.c b/mm/shuffle.c
> index 609c26aa57db0..702c0d5cf276c 100644
> --- a/mm/shuffle.c
> +++ b/mm/shuffle.c
> @@ -10,33 +10,11 @@
>  #include "shuffle.h"
>  
>  DEFINE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
> -static unsigned long shuffle_state __ro_after_init;
> -
> -/*
> - * Depending on the architecture, module parameter parsing may run
> - * before, or after the cache detection. SHUFFLE_FORCE_DISABLE prevents,
> - * or reverts the enabling of the shuffle implementation. SHUFFLE_ENABLE
> - * attempts to turn on the implementation, but aborts if it finds
> - * SHUFFLE_FORCE_DISABLE already set.
> - */
> -__meminit void page_alloc_shuffle(enum mm_shuffle_ctl ctl)
> -{
> -	if (ctl == SHUFFLE_FORCE_DISABLE)
> -		set_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state);
> -
> -	if (test_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state)) {
> -		if (test_and_clear_bit(SHUFFLE_ENABLE, &shuffle_state))
> -			static_branch_disable(&page_alloc_shuffle_key);
> -	} else if (ctl == SHUFFLE_ENABLE
> -			&& !test_and_set_bit(SHUFFLE_ENABLE, &shuffle_state))
> -		static_branch_enable(&page_alloc_shuffle_key);
> -}
>  
>  static bool shuffle_param;
>  static int shuffle_show(char *buffer, const struct kernel_param *kp)
>  {
> -	return sprintf(buffer, "%c\n", test_bit(SHUFFLE_ENABLE, &shuffle_state)
> -			? 'Y' : 'N');
> +	return sprintf(buffer, "%c\n", shuffle_param ? 'Y' : 'N');
>  }
>  
>  static __meminit int shuffle_store(const char *val,
> @@ -47,9 +25,7 @@ static __meminit int shuffle_store(const char *val,
>  	if (rc < 0)
>  		return rc;
>  	if (shuffle_param)
> -		page_alloc_shuffle(SHUFFLE_ENABLE);
> -	else
> -		page_alloc_shuffle(SHUFFLE_FORCE_DISABLE);
> +		static_branch_enable(&page_alloc_shuffle_key);
>  	return 0;
>  }
>  module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
> diff --git a/mm/shuffle.h b/mm/shuffle.h
> index 657e2b9ec38dd..5574cbd4611e3 100644
> --- a/mm/shuffle.h
> +++ b/mm/shuffle.h
> @@ -4,23 +4,10 @@
>  #define _MM_SHUFFLE_H
>  #include <linux/jump_label.h>
>  
> -/*
> - * SHUFFLE_ENABLE is called from the command line enabling path, or by
> - * platform-firmware enabling that indicates the presence of a
> - * direct-mapped memory-side-cache. SHUFFLE_FORCE_DISABLE is called from
> - * the command line path and overrides any previous or future
> - * SHUFFLE_ENABLE.
> - */
> -enum mm_shuffle_ctl {
> -	SHUFFLE_ENABLE,
> -	SHUFFLE_FORCE_DISABLE,
> -};
> -
>  #define SHUFFLE_ORDER (MAX_ORDER-1)
>  
>  #ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR
>  DECLARE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
> -extern void page_alloc_shuffle(enum mm_shuffle_ctl ctl);
>  extern void __shuffle_free_memory(pg_data_t *pgdat);
>  extern bool shuffle_pick_tail(void);
>  static inline void shuffle_free_memory(pg_data_t *pgdat)
> @@ -46,10 +33,6 @@ static inline void shuffle_free_memory(pg_data_t *pgdat)
>  {
>  }
>  
> -static inline void page_alloc_shuffle(enum mm_shuffle_ctl ctl)
> -{
> -}
> -
>  static inline bool is_shuffle_order(int order)
>  {
>  	return false;
> -- 
> 2.26.2

-- 
Michal Hocko
SUSE Labs