[Devel] [PATCH rh7 3/3] tswap: exert equal pressure on tmem and lru pages

[Vladimir Davydov]

shrinker->seeks is supposed to be an estimate of the number of disk
seeks needed to recreate an object. shrink_slab will divide lru scan
ratio over ->seeks to scan objects that need more seeks to be brought
back less intensively.

For most shrinkers (e.g. dcache, icache) ->seeks equals 2 (aka
DEFAULT_SEEKS), because rereading an object requires random IO (you need
seek to the object and seek back), in contrast to page cache which can
benefit from read-ahead. Hence dcache experiences half pressure exerted
upon lru pages.

However, tmem is not like dcache - tmem pages are created from lru pages
so they should receive the same pressure. That said, let's set ->seeks
to 1 for tmem shrinkers.

Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 mm/tswap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/tswap.c b/mm/tswap.c
index dc1253f8e5b2..01953b4e111e 100644
--- a/mm/tswap.c
+++ b/mm/tswap.c
@@ -250,7 +250,7 @@ static unsigned long tswap_shrink_scan(struct shrinker *shrink,
 static struct shrinker tswap_shrinker = {
 	.count_objects = tswap_shrink_count,
 	.scan_objects = tswap_shrink_scan,
-	.seeks = DEFAULT_SEEKS,
+	.seeks = 1,
 	.flags = SHRINKER_NUMA_AWARE,
 };
 
-- 
2.1.4