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[PATCH] LOG2: Implement a general integer log2 facility in the kernel

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This facility provides three entry points:

	ilog2()		Log base 2 of unsigned long
	ilog2_u32()	Log base 2 of u32
	ilog2_u64()	Log base 2 of u64

These facilities can either be used inside functions on dynamic data:

	int do_something(long q)
	{
		...;
		y = ilog2(x)
		...;
	}

Or can be used to statically initialise global variables with constant values:

	unsigned n = ilog2(27);

When performing static initialisation, the compiler will report "error:
initializer element is not constant" if asked to take a log of zero or of
something not reducible to a constant.  They treat negative numbers as
unsigned.

When not dealing with a constant, they fall back to using fls() which permits
them to use arch-specific log calculation instructions - such as BSR on
x86/x86_64 or SCAN on FRV - if available.

[akpm@osdl.org: MMC fix]
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David Howells <dhowells@redhat.com>
Cc: Wojtek Kaniewski <wojtekka@toxygen.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
David Howells 2006-12-08 02:37:49 -08:00 committed by Linus Torvalds
parent b3d7ae5f47
commit f0d1b0b30d
36 changed files with 384 additions and 28 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
arch/alpha/Kconfig
View file

@ -25,6 +25,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/arm/Kconfig
View file

@ -74,6 +74,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/arm26/Kconfig
View file

@ -41,6 +41,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/avr32/Kconfig
View file

@ -45,6 +45,14 @@ config GENERIC_TIME
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_BUST_SPINLOCK
bool

8
arch/cris/Kconfig
View file

@ -16,6 +16,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/frv/Kconfig
View file

@ -41,6 +41,14 @@ config TIME_LOW_RES
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default y
config ARCH_HAS_ILOG2_U64
bool
default y
mainmenu "Fujitsu FR-V Kernel Configuration"
source "init/Kconfig"

8
arch/h8300/Kconfig
View file

@ -29,6 +29,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/i386/Kconfig.cpu
View file

@ -248,6 +248,14 @@ config RWSEM_XCHGADD_ALGORITHM
depends on !M386
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_CALIBRATE_DELAY
bool
default y

8
arch/ia64/Kconfig
View file

@ -34,6 +34,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/m32r/Kconfig
View file

@ -214,6 +214,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/m68k/Kconfig
View file

@ -17,6 +17,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/m68knommu/Kconfig
View file

@ -25,6 +25,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default n
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/mips/Kconfig
View file

@ -819,6 +819,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/parisc/Kconfig
View file

@ -25,6 +25,14 @@ config RWSEM_GENERIC_SPINLOCK
config RWSEM_XCHGADD_ALGORITHM
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_FIND_NEXT_BIT
bool
default y

8
arch/powerpc/Kconfig
View file

@ -41,6 +41,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/ppc/Kconfig
View file

@ -19,6 +19,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default y
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/s390/Kconfig
View file

@ -22,6 +22,14 @@ config RWSEM_XCHGADD_ALGORITHM
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config GENERIC_HWEIGHT
bool
default y

8
arch/sh/Kconfig
View file

@ -59,6 +59,14 @@ config LOCKDEP_SUPPORT
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
source "init/Kconfig"
menu "System type"

8
arch/sh64/Kconfig
View file

@ -39,6 +39,14 @@ config RWSEM_XCHGADD_ALGORITHM
config GENERIC_ISA_DMA
bool
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
source init/Kconfig
menu "System type"

8
arch/sparc/Kconfig
View file

@ -166,6 +166,14 @@ config ARCH_MAY_HAVE_PC_FDC
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config SUN_PM
bool
default y

8
arch/sparc64/Kconfig
View file

@ -34,6 +34,14 @@ config ARCH_MAY_HAVE_PC_FDC
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
config AUDIT_ARCH
bool
default y

8
arch/v850/Kconfig
View file

@ -38,6 +38,14 @@ config TIME_LOW_RES
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
# Turn off some random 386 crap that can affect device config
config ISA
bool

8
arch/x86_64/Kconfig
View file

@ -101,6 +101,14 @@ config GENERIC_BUG
default y
depends on BUG
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
source "init/Kconfig"

8
arch/xtensa/Kconfig
View file

@ -34,6 +34,14 @@ config GENERIC_HARDIRQS
bool
default y
config ARCH_HAS_ILOG2_U32
bool
default n
config ARCH_HAS_ILOG2_U64
bool
default n
source "init/Kconfig"
menu "Processor type and features"

4
drivers/infiniband/hw/mthca/mthca_provider.c
View file

@ -124,7 +124,7 @@ static int mthca_query_device(struct ib_device *ibdev,
props->max_map_per_fmr = 255;
else
props->max_map_per_fmr =
(1 << (32 - long_log2(mdev->limits.num_mpts))) - 1;
(1 << (32 - ilog2(mdev->limits.num_mpts))) - 1;
err = 0;
out:
@ -816,7 +816,7 @@ static int mthca_resize_cq(struct ib_cq *ibcq, int entries, struct ib_udata *uda
lkey = ucmd.lkey;
}
ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, long_log2(entries), &status);
ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, ilog2(entries), &status);
if (status)
ret = -EINVAL;

4
drivers/infiniband/hw/mthca/mthca_qp.c
View file

@ -636,11 +636,11 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask,
if (mthca_is_memfree(dev)) {
if (qp->rq.max)
qp_context->rq_size_stride = long_log2(qp->rq.max) << 3;
qp_context->rq_size_stride = ilog2(qp->rq.max) << 3;
qp_context->rq_size_stride |= qp->rq.wqe_shift - 4;
if (qp->sq.max)
qp_context->sq_size_stride = long_log2(qp->sq.max) << 3;
qp_context->sq_size_stride = ilog2(qp->sq.max) << 3;
qp_context->sq_size_stride |= qp->sq.wqe_shift - 4;
}

4
drivers/infiniband/hw/mthca/mthca_srq.c
View file

@ -120,7 +120,7 @@ static void mthca_arbel_init_srq_context(struct mthca_dev *dev,
memset(context, 0, sizeof *context);
logsize = long_log2(srq->max);
logsize = ilog2(srq->max);
context->state_logsize_srqn = cpu_to_be32(logsize << 24 | srq->srqn);
context->lkey = cpu_to_be32(srq->mr.ibmr.lkey);
context->db_index = cpu_to_be32(srq->db_index);
@ -213,7 +213,7 @@ int mthca_alloc_srq(struct mthca_dev *dev, struct mthca_pd *pd,
if (!mthca_is_memfree(dev) && (ds > dev->limits.max_desc_sz))
return -EINVAL;
srq->wqe_shift = long_log2(ds);
srq->wqe_shift = ilog2(ds);
srq->srqn = mthca_alloc(&dev->srq_table.alloc);
if (srq->srqn == -1)

4
drivers/infiniband/ulp/iser/iser_memory.c
View file

@ -114,7 +114,7 @@ int iser_start_rdma_unaligned_sg(struct iscsi_iser_cmd_task *iser_ctask,
if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
mem = (void *)__get_free_pages(GFP_NOIO,
long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
ilog2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
else
mem = kmalloc(cmd_data_len, GFP_NOIO);
@ -211,7 +211,7 @@ void iser_finalize_rdma_unaligned_sg(struct iscsi_iser_cmd_task *iser_ctask,
if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
free_pages((unsigned long)mem_copy->copy_buf,
long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
ilog2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
else
kfree(mem_copy->copy_buf);

2
drivers/md/dm-crypt.c
View file

@ -220,7 +220,7 @@ static int crypt_iv_benbi_ctr(struct crypt_config *cc, struct dm_target *ti,
const char *opts)
{
unsigned int bs = crypto_blkcipher_blocksize(cc->tfm);
int log = long_log2(bs);
int log = ilog2(bs);
/* we need to calculate how far we must shift the sector count
* to get the cipher block count, we use this shift in _gen */

2
drivers/mmc/tifm_sd.c
View file

@ -387,7 +387,7 @@ static void tifm_sd_prepare_data(struct tifm_sd *card, struct mmc_command *cmd)
writel(TIFM_FIFO_INT_SETALL,
sock->addr + SOCK_DMA_FIFO_INT_ENABLE_CLEAR);
writel(long_log2(cmd->data->blksz) - 2,
writel(ilog2(cmd->data->blksz) - 2,
sock->addr + SOCK_FIFO_PAGE_SIZE);
writel(TIFM_FIFO_ENABLE, sock->addr + SOCK_FIFO_CONTROL);
writel(TIFM_FIFO_INTMASK, sock->addr + SOCK_DMA_FIFO_INT_ENABLE_SET);

6
fs/ext2/super.c
View file

@ -597,8 +597,6 @@ static int ext2_check_descriptors (struct super_block * sb)
return 1;
}
#define log2(n) ffz(~(n))
/*
* Maximal file size. There is a direct, and {,double-,triple-}indirect
* block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
@ -834,9 +832,9 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
sbi->s_sbh = bh;
sbi->s_mount_state = le16_to_cpu(es->s_state);
sbi->s_addr_per_block_bits =
log2 (EXT2_ADDR_PER_BLOCK(sb));
ilog2 (EXT2_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits =
log2 (EXT2_DESC_PER_BLOCK(sb));
ilog2 (EXT2_DESC_PER_BLOCK(sb));
if (sb->s_magic != EXT2_SUPER_MAGIC)
goto cantfind_ext2;

6
fs/ext3/super.c
View file

@ -1347,8 +1347,6 @@ static void ext3_orphan_cleanup (struct super_block * sb,
sb->s_flags = s_flags; /* Restore MS_RDONLY status */
}
#define log2(n) ffz(~(n))
/*
* Maximal file size. There is a direct, and {,double-,triple-}indirect
* block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
@ -1597,8 +1595,8 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
sbi->s_desc_per_block = blocksize / sizeof(struct ext3_group_desc);
sbi->s_sbh = bh;
sbi->s_mount_state = le16_to_cpu(es->s_state);
sbi->s_addr_per_block_bits = log2(EXT3_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits = log2(EXT3_DESC_PER_BLOCK(sb));
sbi->s_addr_per_block_bits = ilog2(EXT3_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits = ilog2(EXT3_DESC_PER_BLOCK(sb));
for (i=0; i < 4; i++)
sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
sbi->s_def_hash_version = es->s_def_hash_version;

44
include/asm-frv/bitops.h
View file

@ -256,6 +256,50 @@ int __ffs(unsigned long x)
return 31 - bit;
}
/*
* special slimline version of fls() for calculating ilog2_u32()
* - note: no protection against n == 0
*/
#define ARCH_HAS_ILOG2_U32
static inline __attribute__((const))
int __ilog2_u32(u32 n)
{
int bit;
asm("scan %1,gr0,%0" : "=r"(bit) : "r"(n));
return 31 - bit;
}
/*
* special slimline version of fls64() for calculating ilog2_u64()
* - note: no protection against n == 0
*/
#define ARCH_HAS_ILOG2_U64
static inline __attribute__((const))
int __ilog2_u64(u64 n)
{
union {
u64 ll;
struct { u32 h, l; };
} _;
int bit, x, y;
_.ll = n;
asm(" subcc %3,gr0,gr0,icc0 \n"
" ckeq icc0,cc4 \n"
" cscan.p %3,gr0,%0 ,cc4,0 \n"
" setlos #63,%1 \n"
" cscan.p %4,gr0,%0 ,cc4,1 \n"
" setlos #31,%2 \n"
" csub.p %1,%0,%0 ,cc4,0 \n"
" csub %2,%0,%0 ,cc4,1 \n"
: "=&r"(bit), "=r"(x), "=r"(y)
: "0r"(_.h), "r"(_.l)
: "icc0", "cc4"
);
return bit;
}
#include <asm-generic/bitops/sched.h>
#include <asm-generic/bitops/hweight.h>

9
include/linux/kernel.h
View file

@ -13,6 +13,7 @@
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/bitops.h>
#include <linux/log2.h>
#include <asm/byteorder.h>
#include <asm/bug.h>
@ -157,14 +158,6 @@ static inline int printk(const char *s, ...) { return 0; }
unsigned long int_sqrt(unsigned long);
static inline int __attribute_pure__ long_log2(unsigned long x)
{
int r = 0;
for (x >>= 1; x > 0; x >>= 1)
r++;
return r;
}
static inline unsigned long
__attribute_const__ roundup_pow_of_two(unsigned long x)
{

131
include/linux/log2.h Normal file
View file

@ -0,0 +1,131 @@
/* Integer base 2 logarithm calculation
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#ifndef _LINUX_LOG2_H
#define _LINUX_LOG2_H
#include <linux/types.h>
#include <linux/bitops.h>
/*
* deal with unrepresentable constant logarithms
*/
extern __attribute__((const, noreturn))
int ____ilog2_NaN(void);
/*
* non-constant log of base 2 calculators
* - the arch may override these in asm/bitops.h if they can be implemented
* more efficiently than using fls() and fls64()
* - the arch is not required to handle n==0 if implementing the fallback
*/
#ifndef CONFIG_ARCH_HAS_ILOG2_U32
static inline __attribute__((const))
int __ilog2_u32(u32 n)
{
return fls(n) - 1;
}
#endif
#ifndef CONFIG_ARCH_HAS_ILOG2_U64
static inline __attribute__((const))
int __ilog2_u64(u64 n)
{
return fls64(n) - 1;
}
#endif
/**
* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
* @n - parameter
*
* constant-capable log of base 2 calculation
* - this can be used to initialise global variables from constant data, hence
* the massive ternary operator construction
*
* selects the appropriately-sized optimised version depending on sizeof(n)
*/
#define ilog2(n) \
( \
__builtin_constant_p(n) ? ( \
(n) < 1 ? ____ilog2_NaN() : \
(n) & (1ULL << 63) ? 63 : \
(n) & (1ULL << 62) ? 62 : \
(n) & (1ULL << 61) ? 61 : \
(n) & (1ULL << 60) ? 60 : \
(n) & (1ULL << 59) ? 59 : \
(n) & (1ULL << 58) ? 58 : \
(n) & (1ULL << 57) ? 57 : \
(n) & (1ULL << 56) ? 56 : \
(n) & (1ULL << 55) ? 55 : \
(n) & (1ULL << 54) ? 54 : \
(n) & (1ULL << 53) ? 53 : \
(n) & (1ULL << 52) ? 52 : \
(n) & (1ULL << 51) ? 51 : \
(n) & (1ULL << 50) ? 50 : \
(n) & (1ULL << 49) ? 49 : \
(n) & (1ULL << 48) ? 48 : \
(n) & (1ULL << 47) ? 47 : \
(n) & (1ULL << 46) ? 46 : \
(n) & (1ULL << 45) ? 45 : \
(n) & (1ULL << 44) ? 44 : \
(n) & (1ULL << 43) ? 43 : \
(n) & (1ULL << 42) ? 42 : \
(n) & (1ULL << 41) ? 41 : \
(n) & (1ULL << 40) ? 40 : \
(n) & (1ULL << 39) ? 39 : \
(n) & (1ULL << 38) ? 38 : \
(n) & (1ULL << 37) ? 37 : \
(n) & (1ULL << 36) ? 36 : \
(n) & (1ULL << 35) ? 35 : \
(n) & (1ULL << 34) ? 34 : \
(n) & (1ULL << 33) ? 33 : \
(n) & (1ULL << 32) ? 32 : \
(n) & (1ULL << 31) ? 31 : \
(n) & (1ULL << 30) ? 30 : \
(n) & (1ULL << 29) ? 29 : \
(n) & (1ULL << 28) ? 28 : \
(n) & (1ULL << 27) ? 27 : \
(n) & (1ULL << 26) ? 26 : \
(n) & (1ULL << 25) ? 25 : \
(n) & (1ULL << 24) ? 24 : \
(n) & (1ULL << 23) ? 23 : \
(n) & (1ULL << 22) ? 22 : \
(n) & (1ULL << 21) ? 21 : \
(n) & (1ULL << 20) ? 20 : \
(n) & (1ULL << 19) ? 19 : \
(n) & (1ULL << 18) ? 18 : \
(n) & (1ULL << 17) ? 17 : \
(n) & (1ULL << 16) ? 16 : \
(n) & (1ULL << 15) ? 15 : \
(n) & (1ULL << 14) ? 14 : \
(n) & (1ULL << 13) ? 13 : \
(n) & (1ULL << 12) ? 12 : \
(n) & (1ULL << 11) ? 11 : \
(n) & (1ULL << 10) ? 10 : \
(n) & (1ULL << 9) ? 9 : \
(n) & (1ULL << 8) ? 8 : \
(n) & (1ULL << 7) ? 7 : \
(n) & (1ULL << 6) ? 6 : \
(n) & (1ULL << 5) ? 5 : \
(n) & (1ULL << 4) ? 4 : \
(n) & (1ULL << 3) ? 3 : \
(n) & (1ULL << 2) ? 2 : \
(n) & (1ULL << 1) ? 1 : \
(n) & (1ULL << 0) ? 0 : \
____ilog2_NaN() \
) : \
(sizeof(n) <= 4) ? \
__ilog2_u32(n) : \
__ilog2_u64(n) \
)
#endif /* _LINUX_LOG2_H */

4
mm/page_alloc.c
View file

@ -3244,7 +3244,7 @@ void *__init alloc_large_system_hash(const char *tablename,
if (numentries > max)
numentries = max;
log2qty = long_log2(numentries);
log2qty = ilog2(numentries);
do {
size = bucketsize << log2qty;
@ -3266,7 +3266,7 @@ void *__init alloc_large_system_hash(const char *tablename,
printk("%s hash table entries: %d (order: %d, %lu bytes)\n",
tablename,
(1U << log2qty),
long_log2(size) - PAGE_SHIFT,
ilog2(size) - PAGE_SHIFT,
size);
if (_hash_shift)