Re: [PATCH 07/25] Check in advance if the zonelist needs additional filtering

[KOSAKI Motohiro]

> Zonelist are filtered based on nodemasks for memory policies normally.
> It can be additionally filters on cpusets if they exist as well as
> noting when zones are full. These simple checks are expensive enough to
> be noticed in profiles. This patch checks in advance if zonelist
> filtering will ever be needed. If not, then the bulk of the checks are
> skipped.
> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> ---
>  include/linux/cpuset.h |    2 ++
>  mm/page_alloc.c        |   37 ++++++++++++++++++++++++++-----------
>  2 files changed, 28 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index a5740fc..978e2f1 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -97,6 +97,8 @@ static inline void set_mems_allowed(nodemask_t nodemask)
>  
>  #else /* !CONFIG_CPUSETS */
>  
> +#define number_of_cpusets (0)
> +
>  static inline int cpuset_init(void) { return 0; }
>  static inline void cpuset_init_smp(void) {}
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c8465d0..3613ba4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1137,7 +1137,11 @@ failed:
>  #define ALLOC_WMARK_HIGH	0x08 /* use pages_high watermark */
>  #define ALLOC_HARDER		0x10 /* try to alloc harder */
>  #define ALLOC_HIGH		0x20 /* __GFP_HIGH set */
> +#ifdef CONFIG_CPUSETS
>  #define ALLOC_CPUSET		0x40 /* check for correct cpuset */
> +#else
> +#define ALLOC_CPUSET		0x00
> +#endif /* CONFIG_CPUSETS */
>  
>  #ifdef CONFIG_FAIL_PAGE_ALLOC
>  
> @@ -1401,6 +1405,7 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
>  	nodemask_t *allowednodes = NULL;/* zonelist_cache approximation */
>  	int zlc_active = 0;		/* set if using zonelist_cache */
>  	int did_zlc_setup = 0;		/* just call zlc_setup() one time */
> +	int zonelist_filter = 0;
>  
>  	(void)first_zones_zonelist(zonelist, high_zoneidx, nodemask,
>  							&preferred_zone);
> @@ -1411,6 +1416,10 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
>  
>  	VM_BUG_ON(order >= MAX_ORDER);
>  
> +	/* Determine in advance if the zonelist needs filtering */
> +	if ((alloc_flags & ALLOC_CPUSET) && unlikely(number_of_cpusets > 1))
> +		zonelist_filter = 1;
> +
>  zonelist_scan:
>  	/*
>  	 * Scan zonelist, looking for a zone with enough free.
> @@ -1418,12 +1427,16 @@ zonelist_scan:
>  	 */
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>  						high_zoneidx, nodemask) {
> -		if (NUMA_BUILD && zlc_active &&
> -			!zlc_zone_worth_trying(zonelist, z, allowednodes))
> -				continue;
> -		if ((alloc_flags & ALLOC_CPUSET) &&
> -			!cpuset_zone_allowed_softwall(zone, gfp_mask))
> -				goto try_next_zone;
> +
> +		/* Ignore the additional zonelist filter checks if possible */
> +		if (zonelist_filter) {
> +			if (NUMA_BUILD && zlc_active &&
> +				!zlc_zone_worth_trying(zonelist, z, allowednodes))
> +					continue;
> +			if ((alloc_flags & ALLOC_CPUSET) &&
> +				!cpuset_zone_allowed_softwall(zone, gfp_mask))
> +					goto try_next_zone;
> +		}

if number_of_cpusets==1, old code call zlc_zone_worth_trying(). but your one never call.
it seems regression.


>  
>  		if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
>  			unsigned long mark;
> @@ -1445,13 +1458,15 @@ zonelist_scan:
>  		if (page)
>  			break;
>  this_zone_full:
> -		if (NUMA_BUILD)
> +		if (NUMA_BUILD && zonelist_filter)
>  			zlc_mark_zone_full(zonelist, z);
>  try_next_zone:
> -		if (NUMA_BUILD && !did_zlc_setup) {
> -			/* we do zlc_setup after the first zone is tried */
> -			allowednodes = zlc_setup(zonelist, alloc_flags);
> -			zlc_active = 1;
> +		if (NUMA_BUILD && zonelist_filter) {
> +			if (!did_zlc_setup) {
> +				/* do zlc_setup after the first zone is tried */
> +				allowednodes = zlc_setup(zonelist, alloc_flags);
> +				zlc_active = 1;
> +			}
>  			did_zlc_setup = 1;
>  		}
>  	}
> -- 
> 1.5.6.5
> 
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