This is a note to let you know that I've just added the patch titled
zcache: Set SWIZ_BITS to 8 to reduce tmem bucket lock contention.
to the 3.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
zcache-set-swiz_bits-to-8-to-reduce-tmem-bucket-lock-contention.patch
and it can be found in the queue-3.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From e8b4553457e78bcff90f70a31212a40a8fd4f0db Mon Sep 17 00:00:00 2001
From: Dan Magenheimer <[email protected]>
Date: Mon, 23 Jan 2012 16:52:20 -0500
Subject: zcache: Set SWIZ_BITS to 8 to reduce tmem bucket lock contention.
From: Dan Magenheimer <[email protected]>
commit e8b4553457e78bcff90f70a31212a40a8fd4f0db upstream.
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 <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/staging/zcache/zcache-main.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1782,9 +1782,9 @@ 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)
Patches currently in stable-queue which might be from
[email protected] are
queue-3.2/zcache-set-swiz_bits-to-8-to-reduce-tmem-bucket-lock-contention.patch
queue-3.2/zcache-fix-deadlock-condition.patch
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