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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>
hifive-unleashed-5.1
Matthew Wilcox 2016-12-14 15:09:22 -08:00 committed by Linus Torvalds
parent 444306129a
commit 424251a4a9
1 changed files with 4 additions and 5 deletions
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9
include/linux/idr.h
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@ -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)