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[PATCH] bitmap: region restructuring 

Restructure the bitmap_*_region() operations, to avoid code duplication.

Also reduces binary text size by about 100 bytes (ia64 arch).  The original
Bottomley bitmap_*_region patch added about 1000 bytes of compiled kernel text
(ia64).  The Mundt multiword extension added another 600 bytes, and this
restructuring patch gets back about 100 bytes.

But the real motivation was the reduced amount of duplicated code.

Tested by Paul Mundt using <= BITS_PER_LONG as well as power of
2 aligned multiword spanning allocations.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Paul Jackson 2006-03-24 03:15:46 -08:00 committed by Linus Torvalds
parent 74373c6acc
commit 3cf64b933c
1 changed files with 103 additions and 98 deletions
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201
lib/bitmap.c
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@ -676,138 +676,143 @@ int bitmap_bitremap(int oldbit, const unsigned long *old,
}
EXPORT_SYMBOL(bitmap_bitremap);
/*
* Common code for bitmap_*_region() routines.
* bitmap: array of unsigned longs corresponding to the bitmap
* pos: the beginning of the region
* order: region size (log base 2 of number of bits)
* reg_op: operation(s) to perform on that region of bitmap
*
* Can set, verify and/or release a region of bits in a bitmap,
* depending on which combination of REG_OP_* flag bits is set.
*
* A region of a bitmap is a sequence of bits in the bitmap, of
* some size '1 << order' (a power of two), aligned to that same
* '1 << order' power of two.
*
* Returns 1 if REG_OP_ISFREE succeeds (region is all zero bits).
* Returns 0 in all other cases and reg_ops.
*/
enum {
REG_OP_ISFREE, /* true if region is all zero bits */
REG_OP_ALLOC, /* set all bits in region */
REG_OP_RELEASE, /* clear all bits in region */
};
static int __reg_op(unsigned long *bitmap, int pos, int order, int reg_op)
{
int nbits_reg; /* number of bits in region */
int index; /* index first long of region in bitmap */
int offset; /* bit offset region in bitmap[index] */
int nlongs_reg; /* num longs spanned by region in bitmap */
int nbitsinlong; /* num bits of region in each spanned long */
unsigned long mask; /* bitmask for one long of region */
int i; /* scans bitmap by longs */
int ret = 0; /* return value */
/*
* Either nlongs_reg == 1 (for small orders that fit in one long)
* or (offset == 0 && mask == ~0UL) (for larger multiword orders.)
*/
nbits_reg = 1 << order;
index = pos / BITS_PER_LONG;
offset = pos - (index * BITS_PER_LONG);
nlongs_reg = BITS_TO_LONGS(nbits_reg);
nbitsinlong = min(nbits_reg, BITS_PER_LONG);
/*
* Can't do "mask = (1UL << nbitsinlong) - 1", as that
* overflows if nbitsinlong == BITS_PER_LONG.
*/
mask = (1UL << (nbitsinlong - 1));
mask += mask - 1;
mask <<= offset;
switch (reg_op) {
case REG_OP_ISFREE:
for (i = 0; i < nlongs_reg; i++) {
if (bitmap[index + i] & mask)
goto done;
}
ret = 1; /* all bits in region free (zero) */
break;
case REG_OP_ALLOC:
for (i = 0; i < nlongs_reg; i++)
bitmap[index + i] |= mask;
break;
case REG_OP_RELEASE:
for (i = 0; i < nlongs_reg; i++)
bitmap[index + i] &= ~mask;
break;
}
done:
return ret;
}
/**
* bitmap_find_free_region - find a contiguous aligned mem region
* @bitmap: an array of unsigned longs corresponding to the bitmap
* @bitmap: array of unsigned longs corresponding to the bitmap
* @bits: number of bits in the bitmap
* @order: region size to find (size is actually 1<<order)
* @order: region size (log base 2 of number of bits) to find
*
* Find a sequence of free (zero) bits in a bitmap and allocate
* them (set them to one). Only consider sequences of length a
* power ('order') of two, aligned to that power of two, which
* Find a region of free (zero) bits in a @bitmap of @bits bits and
* allocate them (set them to one). Only consider regions of length
* a power (@order) of two, aligned to that power of two, which
* makes the search algorithm much faster.
*
* Return the bit offset in bitmap of the allocated sequence,
* Return the bit offset in bitmap of the allocated region,
* or -errno on failure.
*/
int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
{
int nbits; /* number of bits in region */
int nlongs; /* num longs spanned by region in bitmap */
int nbitsinlong; /* num bits of region in each spanned long */
unsigned long mask; /* bitmask of bits [0 .. nbitsinlong-1] */
int i; /* scans bitmap by longs */
int pos; /* scans bitmap by regions of size order */
nbits = 1 << order;
nlongs = (nbits + (BITS_PER_LONG - 1)) / BITS_PER_LONG;
nbitsinlong = nbits;
if (nbitsinlong > BITS_PER_LONG)
nbitsinlong = BITS_PER_LONG;
/* make a mask of the order */
mask = (1UL << (nbitsinlong - 1));
mask += mask - 1;
/* run up the bitmap nbitsinlong at a time */
for (i = 0; i < bits; i += nbitsinlong) {
int index = i / BITS_PER_LONG;
int offset = i - (index * BITS_PER_LONG);
int j, space = 1;
/* find space in the bitmap */
for (j = 0; j < nlongs; j++)
if ((bitmap[index + j] & (mask << offset))) {
space = 0;
break;
}
/* keep looking */
if (unlikely(!space))
continue;
for (j = 0; j < nlongs; j++)
/* set region in bitmap */
bitmap[index + j] |= (mask << offset);
return i;
}
return -ENOMEM;
for (pos = 0; pos < bits; pos += (1 << order))
if (__reg_op(bitmap, pos, order, REG_OP_ISFREE))
break;
if (pos == bits)
return -ENOMEM;
__reg_op(bitmap, pos, order, REG_OP_ALLOC);
return pos;
}
EXPORT_SYMBOL(bitmap_find_free_region);
/**
* bitmap_release_region - release allocated bitmap region
* @bitmap: a pointer to the bitmap
* @pos: the beginning of the region
* @order: the order of the bits to release (number is 1<<order)
* @bitmap: array of unsigned longs corresponding to the bitmap
* @pos: beginning of bit region to release
* @order: region size (log base 2 of number of bits) to release
*
* This is the complement to __bitmap_find_free_region and releases
* the found region (by clearing it in the bitmap).
*
* No return value.
*/
void bitmap_release_region(unsigned long *bitmap, int pos, int order)
{
int nbits; /* number of bits in region */
int nlongs; /* num longs spanned by region in bitmap */
int index; /* index first long of region in bitmap */
int offset; /* bit offset region in bitmap[index] */
int nbitsinlong; /* num bits of region in each spanned long */
unsigned long mask; /* bitmask of bits [0 .. nbitsinlong-1] */
int i; /* scans bitmap by longs */
nbits = 1 << order;
nlongs = (nbits + (BITS_PER_LONG - 1)) / BITS_PER_LONG;
index = pos / BITS_PER_LONG;
offset = pos - (index * BITS_PER_LONG);
nbitsinlong = nbits;
if (nbitsinlong > BITS_PER_LONG)
nbitsinlong = BITS_PER_LONG;
mask = (1UL << (nbitsinlong - 1));
mask += mask - 1;
for (i = 0; i < nlongs; i++)
bitmap[index + i] &= ~(mask << offset);
__reg_op(bitmap, pos, order, REG_OP_RELEASE);
}
EXPORT_SYMBOL(bitmap_release_region);
/**
* bitmap_allocate_region - allocate bitmap region
* @bitmap: a pointer to the bitmap
* @pos: the beginning of the region
* @order: the order of the bits to allocate (number is 1<<order)
* @bitmap: array of unsigned longs corresponding to the bitmap
* @pos: beginning of bit region to allocate
* @order: region size (log base 2 of number of bits) to allocate
*
* Allocate (set bits in) a specified region of a bitmap.
*
* Return 0 on success, or -EBUSY if specified region wasn't
* free (not all bits were zero).
*/
int bitmap_allocate_region(unsigned long *bitmap, int pos, int order)
{
int nbits; /* number of bits in region */
int nlongs; /* num longs spanned by region in bitmap */
int index; /* index first long of region in bitmap */
int offset; /* bit offset region in bitmap[index] */
int nbitsinlong; /* num bits of region in each spanned long */
unsigned long mask; /* bitmask of bits [0 .. nbitsinlong-1] */
int i; /* scans bitmap by longs */
nbits = 1 << order;
nlongs = (nbits + (BITS_PER_LONG - 1)) / BITS_PER_LONG;
index = pos / BITS_PER_LONG;
offset = pos - (index * BITS_PER_LONG);
nbitsinlong = nbits;
if (nbitsinlong > BITS_PER_LONG)
nbitsinlong = BITS_PER_LONG;
mask = (1UL << (nbitsinlong - 1));
mask += mask - 1;
for (i = 0; i < nlongs; i++)
if (bitmap[index + i] & (mask << offset))
return -EBUSY;
for (i = 0; i < nlongs; i++)
bitmap[index + i] |= (mask << offset);
if (!__reg_op(bitmap, pos, order, REG_OP_ISFREE))
return -EBUSY;
__reg_op(bitmap, pos, order, REG_OP_ALLOC);
return 0;
}
EXPORT_SYMBOL(bitmap_allocate_region);