From: Seth Jennings <sjenning@linux.vnet.ibm.com>
To: greg@kroah.com
Cc: gregkh@suse.de, cascardo@holoscopio.com,
dan.magenheimer@oracle.com, rdunlap@xenotime.net,
devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org,
brking@linux.vnet.ibm.com, rcj@linux.vnet.ibm.com,
Seth Jennings <sjenning@linux.vnet.ibm.com>
Subject: [PATCH] staging: zcache: reduce tmem bucket lock contention
Date: Tue, 4 Oct 2011 08:21:32 -0500 [thread overview]
Message-ID: <1317734492-22165-1-git-send-email-sjenning@linux.vnet.ibm.com> (raw)
In-Reply-To: <20111003230632.GA12719@kroah.com>
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 <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
---
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
prev parent reply other threads:[~2011-10-04 13:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-29 14:32 [PATCH] staging: zcache: reduce tmem bucket lock contention Seth Jennings
2011-10-03 18:51 ` Dan Magenheimer
2011-10-03 23:06 ` Greg KH
2011-10-04 13:21 ` Seth Jennings [this message]
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