[PATCH -mm -v2 2/6] mm, swap: Add swap readahead hit statistics

Huang, Ying
2017-06-30T01:44:55Z

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: 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>
---
mm/swap_state.c | 30 ++++++++++++++++++++++++++++--
1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index a13bbf504e93..6739343a3695 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -74,6 +74,8 @@ unsigned long total_swapcache_pages(void)
}

static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
+static atomic_long_t swapin_readahead_hits_total = ATOMIC_INIT(0);
+static atomic_long_t swapin_readahead_total = ATOMIC_INIT(0);

void show_swap_cache_info(void)
{
@@ -305,8 +307,10 @@ 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);
+ atomic_long_inc(&swapin_readahead_hits_total);
+ }
}

INC_CACHE_INFO(find_total);
@@ -516,8 +520,11 @@ 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);
+ atomic_long_inc(&swapin_readahead_total);
+ }
put_page(page);
}
blk_finish_plug(&plug);
@@ -603,12 +610,31 @@ static ssize_t swap_cache_find_total_show(
static struct kobj_attribute swap_cache_find_total_attr =
__ATTR(cache_find_total, 0444, swap_cache_find_total_show, NULL);

+static ssize_t swap_readahead_hits_show(
+ struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%ld\n",
+ atomic_long_read(&swapin_readahead_hits_total));
+}
+static struct kobj_attribute swap_readahead_hits_attr =
+ __ATTR(ra_hits, 0444, swap_readahead_hits_show, NULL);
+
+static ssize_t swap_readahead_total_show(
+ struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%ld\n", atomic_long_read(&swapin_readahead_total));
+}
+static struct kobj_attribute swap_readahead_total_attr =
+ __ATTR(ra_total, 0444, swap_readahead_total_show, NULL);
+
static struct attribute *swap_attrs[] = {
&swap_cache_pages_attr.attr,
&swap_cache_add_attr.attr,
&swap_cache_del_attr.attr,
&swap_cache_find_success_attr.attr,
&swap_cache_find_total_attr.attr,
+ &swap_readahead_hits_attr.attr,
+ &swap_readahead_total_attr.attr,
NULL,
};

--
2.11.0