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authorDan Magenheimer <dan.magenheimer@oracle.com>2012-01-23 16:52:20 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-02-08 14:14:12 -0800
commite8b4553457e78bcff90f70a31212a40a8fd4f0db (patch)
tree45b487b66aff49bd3c14b1d25866b0a6c519ae3c /drivers/staging/zcache
parent9256a4789be3dae37d00924c03546ba7958ea5a3 (diff)
zcache: Set SWIZ_BITS to 8 to reduce tmem bucket lock contention.
SWIZ_BITS > 8 results in a much larger number of "tmem_obj" allocations, likely one per page-placed-in-frontswap. The tmem_obj is not huge (roughly 100 bytes), but it is large enough to add a not-insignificant memory overhead to zcache. The SWIZ_BITS=8 will get roughly the same lock contention without the space wastage. The effect of SWIZ_BITS can be thought of as "2^SWIZ_BITS is the number of unique oids that be generated" (This concept is limited to frontswap's use of tmem). Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: stable <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/staging/zcache')
-rw-r--r--drivers/staging/zcache/zcache-main.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index ae0ed82dd3cb..ce07087750a6 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1781,9 +1781,9 @@ 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()
+ * frontswap_get_page(), but has side-effects. Hence using 8.
*/
-#define SWIZ_BITS 27
+#define SWIZ_BITS 8
#define SWIZ_MASK ((1 << SWIZ_BITS) - 1)
#define _oswiz(_type, _ind) ((_type << SWIZ_BITS) | (_ind & SWIZ_MASK))
#define iswiz(_ind) (_ind >> SWIZ_BITS)