Re: [PATCH 1/1] mm: vmstat: introducing vm counter for slowpath

[Sergey Senozhatsky]

On (08/07/15 12:38), Pintu Kumar wrote:
> This patch add new counter slowpath_entered in /proc/vmstat to
> track how many times the system entered into slowpath after
> first allocation attempt is failed.
> This is useful to know the rate of allocation success within
> the slowpath.
> This patch is tested on ARM with 512MB RAM.
> A sample output is shown below after successful boot-up:
> shell> cat /proc/vmstat
> nr_free_pages 4712
> pgalloc_normal 1319432
> pgalloc_movable 0
> pageoutrun 379
> allocstall 0
> slowpath_entered 585
> compact_stall 0
> compact_fail 0
> compact_success 0
> 
> From the above output we can see that the system entered
> slowpath 585 times.

so what can you do with this number?

	-ss

> But the existing counter kswapd(pageoutrun), direct_reclaim(allocstall),
> direct_compact(compact_stall) does not tell this value.
> From the above value, it clearly indicates that the system have
> entered slowpath 585 times. Out of which 379 times allocation passed
> through kswapd, without performing direct reclaim/compaction.
> That means the remaining 206 times the allocation would have succeeded
> using the alloc_pages_high_priority.
> 
> Signed-off-by: Pintu Kumar <pintu.k@xxxxxxxxxxx>
> ---
>  include/linux/vm_event_item.h |    2 +-
>  mm/page_alloc.c               |    2 ++
>  mm/vmstat.c                   |    2 +-
>  3 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 2b1cef8..9825f294 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -37,7 +37,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  #endif
>  		PGINODESTEAL, SLABS_SCANNED, KSWAPD_INODESTEAL,
>  		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
> -		PAGEOUTRUN, ALLOCSTALL, PGROTATED,
> +		PAGEOUTRUN, ALLOCSTALL, SLOWPATH_ENTERED, PGROTATED,
>  		DROP_PAGECACHE, DROP_SLAB,
>  #ifdef CONFIG_NUMA_BALANCING
>  		NUMA_PTE_UPDATES,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2024d2e..4a5d487 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3029,6 +3029,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	if (IS_ENABLED(CONFIG_NUMA) && (gfp_mask & __GFP_THISNODE) && !wait)
>  		goto nopage;
>  
> +	count_vm_event(SLOWPATH_ENTERED);
> +
>  retry:
>  	if (!(gfp_mask & __GFP_NO_KSWAPD))
>  		wake_all_kswapds(order, ac);
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 1fd0886..1c54fdf 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -778,7 +778,7 @@ const char * const vmstat_text[] = {
>  	"kswapd_high_wmark_hit_quickly",
>  	"pageoutrun",
>  	"allocstall",
> -
> +	"slowpath_entered",
>  	"pgrotated",
>  
>  	"drop_pagecache",
> -- 
> 1.7.9.5
> 
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