| From | Matthew Wilcox <> | Subject | [PATCH v3 31/33] idr: Reduce the number of bits per level from 8 to 6 | Date | Mon, 28 Nov 2016 13:50:35 -0800 |
| |
From: Matthew Wilcox <willy@linux.intel.com>
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@linux.intel.com> --- 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
|