[Devel] [PATCH rh7 2/3] tcache: 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/tcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/tcache.c b/mm/tcache.c
index e8ffa91190e6..b8757cf354a9 100644
--- a/mm/tcache.c
+++ b/mm/tcache.c
@@ -817,7 +817,7 @@ static unsigned long tcache_shrink_scan(struct shrinker *shrink,
 struct shrinker tcache_shrinker = {
 	.count_objects		= tcache_shrink_count,
 	.scan_objects		= tcache_shrink_scan,
-	.seeks			= DEFAULT_SEEKS,
+	.seeks			= 1,
 	.flags			= SHRINKER_NUMA_AWARE,
 };
 
-- 
2.1.4