The patch titled
Subject: idr: reduce the number of bits per level from 8 to 6
has been added to the -mm tree. Its filename is
idr-reduce-the-number-of-bits-per-level-from-8-to-6.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/idr-reduce-the-number-of-bits-per-level-from-8-to-6.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/idr-reduce-the-number-of-bits-per-level-from-8-to-6.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Subject: idr: reduce the number of bits per level from 8 to 6
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.
Link: http://lkml.kernel.org/r/1480369871-5271-66-git-send-email-mawilcox@xxxxxxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Tested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/idr.h | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff -puN include/linux/idr.h~idr-reduce-the-number-of-bits-per-level-from-8-to-6 include/linux/idr.h
--- a/include/linux/idr.h~idr-reduce-the-number-of-bits-per-level-from-8-to-6
+++ a/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)
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxxxx are
tools-add-warn_on_once.patch
radix-tree-test-suite-allow-gfp_atomic-allocations-to-fail.patch
tools-add-more-bitmap-functions.patch
radix-tree-test-suite-use-common-find-bit-code.patch
radix-tree-fix-typo.patch
radix-tree-create-node_tag_set.patch
radix-tree-make-radix_tree_find_next_bit-more-useful.patch
radix-tree-add-radix_tree_join.patch
radix-tree-add-radix_tree_split.patch
radix-tree-add-radix_tree_split_preload.patch
idr-add-ida_is_empty.patch
idr-reduce-the-number-of-bits-per-level-from-8-to-6.patch
radix-tree-test-suite-add-some-more-functionality.patch
reimplement-idr-and-ida-using-the-radix-tree.patch
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