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Fix bitmap_ffu() to work with 3+ levels.

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This commit is contained in:
Jason Evans 2017-03-27 01:52:20 -07:00
parent 735ad8210c
commit 6258176c87
2 changed files with 58 additions and 43 deletions
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74
include/jemalloc/internal/bitmap_inlines.h
View File

@ -83,52 +83,40 @@ bitmap_ffu(const bitmap_t *bitmap, const bitmap_info_t *binfo, size_t min_bit) {
assert(min_bit < binfo->nbits);
#ifdef BITMAP_USE_TREE
unsigned level = binfo->nlevels - 1;
size_t lg_bits_per_group = (LG_BITMAP_GROUP_NBITS * (level+1));
size_t bits_per_group = 1LU << lg_bits_per_group;
size_t bits_per_group_mask = bits_per_group - 1;
unsigned group_nmask = (min_bit & bits_per_group_mask) >> (level *
LG_BITMAP_GROUP_NBITS);
bitmap_t group_mask = ~((1LU << group_nmask) - 1);
bitmap_t group = bitmap[binfo->levels[level].group_offset] & group_mask;
if (group == 0LU) {
return binfo->nbits;
}
size_t bit = ffs_lu(group) - 1;
while (level > 0) {
level--;
lg_bits_per_group = (LG_BITMAP_GROUP_NBITS * (level+1));
bits_per_group = 1LU << lg_bits_per_group;
bits_per_group_mask = bits_per_group - 1;
group = bitmap[binfo->levels[level].group_offset + bit];
size_t cur_base = bit << lg_bits_per_group;
if (cur_base < min_bit) {
group_nmask = (min_bit & bits_per_group_mask) >> (level
* LG_BITMAP_GROUP_NBITS);
group_mask = ~((1LU << group_nmask) - 1);
group &= group_mask;
}
if (group == 0LU) {
/*
* If min_bit is not the first bit in its group, try
* again starting at the first bit of the next group.
* This will only recurse at most once, since on
* recursion, min_bit will be the first bit in its
* group.
*/
size_t ceil_min_bit = (min_bit +
BITMAP_GROUP_NBITS_MASK) & ~BITMAP_GROUP_NBITS_MASK;
if (ceil_min_bit != min_bit && ceil_min_bit <
binfo->nbits) {
return bitmap_ffu(bitmap, binfo, ceil_min_bit);
size_t bit = 0;
for (unsigned level = binfo->nlevels; level--;) {
size_t lg_bits_per_group = (LG_BITMAP_GROUP_NBITS * (level +
1));
bitmap_t group = bitmap[binfo->levels[level].group_offset + (bit
>> lg_bits_per_group)];
unsigned group_nmask = ((min_bit > bit) ? (min_bit - bit) : 0)
>> (lg_bits_per_group - LG_BITMAP_GROUP_NBITS);
assert(group_nmask <= BITMAP_GROUP_NBITS);
bitmap_t group_mask = ~((1LU << group_nmask) - 1);
bitmap_t group_masked = group & group_mask;
if (group_masked == 0LU) {
if (group == 0LU) {
return binfo->nbits;
}
return binfo->nbits;
/*
* min_bit was preceded by one or more unset bits in
* this group, but there are no other unset bits in this
* group. Try again starting at the first bit of the
* next sibling. This will recurse at most once per
* non-root level.
*/
size_t sib_base = bit + (1U << lg_bits_per_group);
assert(sib_base > min_bit);
assert(sib_base > bit);
if (sib_base >= binfo->nbits) {
return binfo->nbits;
}
return bitmap_ffu(bitmap, binfo, sib_base);
}
bit = (bit << LG_BITMAP_GROUP_NBITS) + (ffs_lu(group) - 1);
bit += (ffs_lu(group_masked) - 1) << (lg_bits_per_group -
LG_BITMAP_GROUP_NBITS);
}
assert(bit >= min_bit);
assert(bit < binfo->nbits);
return bit;
#else

27
test/unit/bitmap.c
View File

@ -372,6 +372,33 @@ test_bitmap_xfu_body(const bitmap_info_t *binfo, size_t nbits) {
}
}
/*
* Unset the last bit, bubble another unset bit through the bitmap, and
* verify that bitmap_ffu() finds the correct bit for all four min_bit
* cases.
*/
if (nbits >= 3) {
bitmap_unset(bitmap, binfo, nbits-1);
for (size_t i = 0; i < nbits-1; i++) {
bitmap_unset(bitmap, binfo, i);
if (i > 0) {
assert_zu_eq(bitmap_ffu(bitmap, binfo, i-1), i,
"Unexpected first unset bit");
}
assert_zu_eq(bitmap_ffu(bitmap, binfo, i), i,
"Unexpected first unset bit");
assert_zu_eq(bitmap_ffu(bitmap, binfo, i+1), nbits-1,
"Unexpected first unset bit");
assert_zu_eq(bitmap_ffu(bitmap, binfo, nbits-1),
nbits-1, "Unexpected first unset bit");
assert_zu_eq(bitmap_sfu(bitmap, binfo), i,
"Unexpected first unset bit");
}
assert_zu_eq(bitmap_sfu(bitmap, binfo), nbits-1,
"Unexpected first unset bit");
}
free(bitmap);
}