From: Huang Ying <ying.hu...@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.hu...@intel.com>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Minchan Kim <minc...@kernel.org>
Cc: Rik van Riel <r...@redhat.com>
Cc: Shaohua Li <s...@kernel.org>
Cc: Hugh Dickins <hu...@google.com>
Cc: Fengguang Wu <fengguang...@intel.com>
Cc: Tim Chen <tim.c.c...@intel.com>
Cc: Dave Hansen <dave.han...@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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