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Date: Wed, 9 Aug 2017 14:50:42 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan@kernel.org>,
        Rik van Riel <riel@redhat.com>, Shaohua Li <shli@kernel.org>,
        Hugh Dickins <hughd@google.com>, Fengguang Wu <fengguang.wu@intel.com>,
        Tim Chen <tim.c.chen@intel.com>, Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH -mm -v4 1/5] mm, swap: Add swap readahead hit statistics
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        <20170807054038.1843-2-ying.huang@intel.com>
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On Mon,  7 Aug 2017 13:40:34 +0800 "Huang, Ying" <ying.huang@intel.com> wrote:

> From: Huang Ying <ying.huang@intel.com>
> 
> The statistics for total readahead pages and total readahead hits are
> recorded and exported via the following sysfs interface.
> 
> /sys/kernel/mm/swap/ra_hits
> /sys/kernel/mm/swap/ra_total
> 
> With them, the efficiency of the swap readahead could be measured, so
> that the swap readahead algorithm and parameters could be tuned
> accordingly.
> 
> ...
>
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -106,6 +106,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  		VMACACHE_FIND_HITS,
>  		VMACACHE_FULL_FLUSHES,
>  #endif
> +		SWAP_RA,
> +		SWAP_RA_HIT,
>  		NR_VM_EVENT_ITEMS
>  };

swap_state.o isn't even compiled if CONFIG_SWAP=n so there doesn't seem
much point in displaying these?

--- a/include/linux/vm_event_item.h~mm-swap-add-swap-readahead-hit-statistics-fix
+++ a/include/linux/vm_event_item.h
@@ -106,8 +106,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
 		VMACACHE_FIND_HITS,
 		VMACACHE_FULL_FLUSHES,
 #endif
+#ifdef CONFIG_SWAP
 		SWAP_RA,
 		SWAP_RA_HIT,
+#endif
 		NR_VM_EVENT_ITEMS
 };
 
--- a/mm/vmstat.c~mm-swap-add-swap-readahead-hit-statistics-fix
+++ a/mm/vmstat.c
@@ -1098,9 +1098,10 @@ const char * const vmstat_text[] = {
 	"vmacache_find_hits",
 	"vmacache_full_flushes",
 #endif
-
+#ifdef CONFIG_SWAP
 	"swap_ra",
 	"swap_ra_hit",
+#endif
 #endif /* CONFIG_VM_EVENTS_COUNTERS */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */
_