tmem uses hash buckets each with their own rbtree and lock to quickly lookup tmem objects. tmem has TMEM_HASH_BUCKETS (256) buckets per pool. However, because of the way the tmem_oid is generated for frontswap pages, only 16 unique tmem_oids are being generated, resulting in only 16 of the 256 buckets being used. This cause high lock contention for the per bucket locks.
This patch changes SWIZ_BITS to include more bits of the offset. The result is that all 256 hash buckets are potentially used resulting in a 95% drop in hash bucket lock contention. Based on v3.1-rc7 Signed-off-by: Seth Jennings <[email protected]> Acked-by: Dan Magenheimer <[email protected]> --- drivers/staging/zcache/zcache-main.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c index 462fbc2..b4b692f 100644 --- a/drivers/staging/zcache/zcache-main.c +++ b/drivers/staging/zcache/zcache-main.c @@ -1798,8 +1798,10 @@ static int zcache_frontswap_poolid = -1; /* * Swizzling increases objects per swaptype, increasing tmem concurrency * for heavy swaploads. Later, larger nr_cpus -> larger SWIZ_BITS + * Setting SWIZ_BITS to 27 basically reconstructs the swap entry from + * frontswap_get_page() */ -#define SWIZ_BITS 4 +#define SWIZ_BITS 27 #define SWIZ_MASK ((1 << SWIZ_BITS) - 1) #define _oswiz(_type, _ind) ((_type << SWIZ_BITS) | (_ind & SWIZ_MASK)) #define iswiz(_ind) (_ind >> SWIZ_BITS) -- 1.7.4.1 _______________________________________________ devel mailing list [email protected] http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
