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