[PATCH -mm -v4 1/5] mm, swap: Add swap readahead hit statistics

["Huang, Ying" <ying.huang@intel.com>]

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.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
---
 include/linux/vm_event_item.h | 2 ++
 mm/swap_state.c               | 9 +++++++--
 mm/vmstat.c                   | 3 +++
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index e02820fc2861..27e3339cfd65 100644
--- 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
 };
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index b68c93014f50..d1bdb31cab13 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -305,8 +305,10 @@ struct page * lookup_swap_cache(swp_entry_t entry)
 
 	if (page && likely(!PageTransCompound(page))) {
 		INC_CACHE_INFO(find_success);
-		if (TestClearPageReadahead(page))
+		if (TestClearPageReadahead(page)) {
 			atomic_inc(&swapin_readahead_hits);
+			count_vm_event(SWAP_RA_HIT);
+		}
 	}
 
 	INC_CACHE_INFO(find_total);
@@ -516,8 +518,11 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 						gfp_mask, vma, addr, false);
 		if (!page)
 			continue;
-		if (offset != entry_offset && likely(!PageTransCompound(page)))
+		if (offset != entry_offset &&
+		    likely(!PageTransCompound(page))) {
 			SetPageReadahead(page);
+			count_vm_event(SWAP_RA);
+		}
 		put_page(page);
 	}
 	blk_finish_plug(&plug);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index ba9b202e8500..4c2121a8b877 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1095,6 +1095,9 @@ const char * const vmstat_text[] = {
 	"vmacache_find_hits",
 	"vmacache_full_flushes",
 #endif
+
+	"swap_ra",
+	"swap_ra_hit",
 #endif /* CONFIG_VM_EVENTS_COUNTERS */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */
-- 
2.11.0

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