[PATCH 26/29] idr: Reduce the number of bits per level from 8 to 6

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>

In preparation for merging the IDR and radix tree, reduce the fanout at
each level from 256 to 64.  If this causes a performance problem then
a bisect will point to this commit, and we'll have a better idea about
what we might do to fix it.

Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
---
 include/linux/idr.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index 1eb755f..3c01b89 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -18,12 +18,11 @@
 #include <linux/rcupdate.h>
 
 /*
- * We want shallower trees and thus more bits covered at each layer.  8
- * bits gives us large enough first layer for most use cases and maximum
- * tree depth of 4.  Each idr_layer is slightly larger than 2k on 64bit and
- * 1k on 32bit.
+ * Using 6 bits at each layer allows us to allocate 7 layers out of each page.
+ * 8 bits only gave us 3 layers out of every pair of pages, which is less
+ * efficient except for trees with a largest element between 192-255 inclusive.
  */
-#define IDR_BITS 8
+#define IDR_BITS 6
 #define IDR_SIZE (1 << IDR_BITS)
 #define IDR_MASK ((1 << IDR_BITS)-1)
 
-- 
2.10.2

--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux