Commit 424251a4 authored Dec 14, 2016 by Matthew Wilcox Committed by Linus Torvalds Dec 14, 2016

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@linuxonhyperv.com


Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 44430612

include/linux/idr.h

+4 −5

Original line number	Diff line number	Diff line
		@@ -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)