qemu/util/hbitmap.c
Max Reitz 6725f887ac hbitmap: Fix shifts of constants by granularity
An hbitmap's granularity may be anything from 0 to 63, so when shifting
constants by its value, they should not be plain ints.

Even having changed the types, hbitmap_serialization_granularity() still
tries to shift 64 to the right by the granularity. This operation is
undefined if the granularity is greater than 57. Adding an assertion is
fine for now, because serializing is done only in tests so far, but this
means that only bitmaps with a granularity below 58 can be serialized
and we should thus add a hbitmap_is_serializable() function later.

One of the two places touched in this patch uses
QEMU_ALIGN_UP(x, 1 << y). We can use ROUND_UP() there, since the second
parameter is obviously a power of two.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20161115224732.1334-1-mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
2016-11-29 17:46:36 +08:00

676 lines
20 KiB
C

/*
* Hierarchical Bitmap Data Type
*
* Copyright Red Hat, Inc., 2012
*
* Author: Paolo Bonzini <pbonzini@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or
* later. See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "qemu/hbitmap.h"
#include "qemu/host-utils.h"
#include "trace.h"
/* HBitmaps provides an array of bits. The bits are stored as usual in an
* array of unsigned longs, but HBitmap is also optimized to provide fast
* iteration over set bits; going from one bit to the next is O(logB n)
* worst case, with B = sizeof(long) * CHAR_BIT: the result is low enough
* that the number of levels is in fact fixed.
*
* In order to do this, it stacks multiple bitmaps with progressively coarser
* granularity; in all levels except the last, bit N is set iff the N-th
* unsigned long is nonzero in the immediately next level. When iteration
* completes on the last level it can examine the 2nd-last level to quickly
* skip entire words, and even do so recursively to skip blocks of 64 words or
* powers thereof (32 on 32-bit machines).
*
* Given an index in the bitmap, it can be split in group of bits like
* this (for the 64-bit case):
*
* bits 0-57 => word in the last bitmap | bits 58-63 => bit in the word
* bits 0-51 => word in the 2nd-last bitmap | bits 52-57 => bit in the word
* bits 0-45 => word in the 3rd-last bitmap | bits 46-51 => bit in the word
*
* So it is easy to move up simply by shifting the index right by
* log2(BITS_PER_LONG) bits. To move down, you shift the index left
* similarly, and add the word index within the group. Iteration uses
* ffs (find first set bit) to find the next word to examine; this
* operation can be done in constant time in most current architectures.
*
* Setting or clearing a range of m bits on all levels, the work to perform
* is O(m + m/W + m/W^2 + ...), which is O(m) like on a regular bitmap.
*
* When iterating on a bitmap, each bit (on any level) is only visited
* once. Hence, The total cost of visiting a bitmap with m bits in it is
* the number of bits that are set in all bitmaps. Unless the bitmap is
* extremely sparse, this is also O(m + m/W + m/W^2 + ...), so the amortized
* cost of advancing from one bit to the next is usually constant (worst case
* O(logB n) as in the non-amortized complexity).
*/
struct HBitmap {
/* Number of total bits in the bottom level. */
uint64_t size;
/* Number of set bits in the bottom level. */
uint64_t count;
/* A scaling factor. Given a granularity of G, each bit in the bitmap will
* will actually represent a group of 2^G elements. Each operation on a
* range of bits first rounds the bits to determine which group they land
* in, and then affect the entire page; iteration will only visit the first
* bit of each group. Here is an example of operations in a size-16,
* granularity-1 HBitmap:
*
* initial state 00000000
* set(start=0, count=9) 11111000 (iter: 0, 2, 4, 6, 8)
* reset(start=1, count=3) 00111000 (iter: 4, 6, 8)
* set(start=9, count=2) 00111100 (iter: 4, 6, 8, 10)
* reset(start=5, count=5) 00000000
*
* From an implementation point of view, when setting or resetting bits,
* the bitmap will scale bit numbers right by this amount of bits. When
* iterating, the bitmap will scale bit numbers left by this amount of
* bits.
*/
int granularity;
/* A meta dirty bitmap to track the dirtiness of bits in this HBitmap. */
HBitmap *meta;
/* A number of progressively less coarse bitmaps (i.e. level 0 is the
* coarsest). Each bit in level N represents a word in level N+1 that
* has a set bit, except the last level where each bit represents the
* actual bitmap.
*
* Note that all bitmaps have the same number of levels. Even a 1-bit
* bitmap will still allocate HBITMAP_LEVELS arrays.
*/
unsigned long *levels[HBITMAP_LEVELS];
/* The length of each levels[] array. */
uint64_t sizes[HBITMAP_LEVELS];
};
/* Advance hbi to the next nonzero word and return it. hbi->pos
* is updated. Returns zero if we reach the end of the bitmap.
*/
unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi)
{
size_t pos = hbi->pos;
const HBitmap *hb = hbi->hb;
unsigned i = HBITMAP_LEVELS - 1;
unsigned long cur;
do {
cur = hbi->cur[--i];
pos >>= BITS_PER_LEVEL;
} while (cur == 0);
/* Check for end of iteration. We always use fewer than BITS_PER_LONG
* bits in the level 0 bitmap; thus we can repurpose the most significant
* bit as a sentinel. The sentinel is set in hbitmap_alloc and ensures
* that the above loop ends even without an explicit check on i.
*/
if (i == 0 && cur == (1UL << (BITS_PER_LONG - 1))) {
return 0;
}
for (; i < HBITMAP_LEVELS - 1; i++) {
/* Shift back pos to the left, matching the right shifts above.
* The index of this word's least significant set bit provides
* the low-order bits.
*/
assert(cur);
pos = (pos << BITS_PER_LEVEL) + ctzl(cur);
hbi->cur[i] = cur & (cur - 1);
/* Set up next level for iteration. */
cur = hb->levels[i + 1][pos];
}
hbi->pos = pos;
trace_hbitmap_iter_skip_words(hbi->hb, hbi, pos, cur);
assert(cur);
return cur;
}
void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first)
{
unsigned i, bit;
uint64_t pos;
hbi->hb = hb;
pos = first >> hb->granularity;
assert(pos < hb->size);
hbi->pos = pos >> BITS_PER_LEVEL;
hbi->granularity = hb->granularity;
for (i = HBITMAP_LEVELS; i-- > 0; ) {
bit = pos & (BITS_PER_LONG - 1);
pos >>= BITS_PER_LEVEL;
/* Drop bits representing items before first. */
hbi->cur[i] = hb->levels[i][pos] & ~((1UL << bit) - 1);
/* We have already added level i+1, so the lowest set bit has
* been processed. Clear it.
*/
if (i != HBITMAP_LEVELS - 1) {
hbi->cur[i] &= ~(1UL << bit);
}
}
}
bool hbitmap_empty(const HBitmap *hb)
{
return hb->count == 0;
}
int hbitmap_granularity(const HBitmap *hb)
{
return hb->granularity;
}
uint64_t hbitmap_count(const HBitmap *hb)
{
return hb->count << hb->granularity;
}
/* Count the number of set bits between start and end, not accounting for
* the granularity. Also an example of how to use hbitmap_iter_next_word.
*/
static uint64_t hb_count_between(HBitmap *hb, uint64_t start, uint64_t last)
{
HBitmapIter hbi;
uint64_t count = 0;
uint64_t end = last + 1;
unsigned long cur;
size_t pos;
hbitmap_iter_init(&hbi, hb, start << hb->granularity);
for (;;) {
pos = hbitmap_iter_next_word(&hbi, &cur);
if (pos >= (end >> BITS_PER_LEVEL)) {
break;
}
count += ctpopl(cur);
}
if (pos == (end >> BITS_PER_LEVEL)) {
/* Drop bits representing the END-th and subsequent items. */
int bit = end & (BITS_PER_LONG - 1);
cur &= (1UL << bit) - 1;
count += ctpopl(cur);
}
return count;
}
/* Setting starts at the last layer and propagates up if an element
* changes.
*/
static inline bool hb_set_elem(unsigned long *elem, uint64_t start, uint64_t last)
{
unsigned long mask;
unsigned long old;
assert((last >> BITS_PER_LEVEL) == (start >> BITS_PER_LEVEL));
assert(start <= last);
mask = 2UL << (last & (BITS_PER_LONG - 1));
mask -= 1UL << (start & (BITS_PER_LONG - 1));
old = *elem;
*elem |= mask;
return old != *elem;
}
/* The recursive workhorse (the depth is limited to HBITMAP_LEVELS)...
* Returns true if at least one bit is changed. */
static bool hb_set_between(HBitmap *hb, int level, uint64_t start,
uint64_t last)
{
size_t pos = start >> BITS_PER_LEVEL;
size_t lastpos = last >> BITS_PER_LEVEL;
bool changed = false;
size_t i;
i = pos;
if (i < lastpos) {
uint64_t next = (start | (BITS_PER_LONG - 1)) + 1;
changed |= hb_set_elem(&hb->levels[level][i], start, next - 1);
for (;;) {
start = next;
next += BITS_PER_LONG;
if (++i == lastpos) {
break;
}
changed |= (hb->levels[level][i] == 0);
hb->levels[level][i] = ~0UL;
}
}
changed |= hb_set_elem(&hb->levels[level][i], start, last);
/* If there was any change in this layer, we may have to update
* the one above.
*/
if (level > 0 && changed) {
hb_set_between(hb, level - 1, pos, lastpos);
}
return changed;
}
void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t count)
{
/* Compute range in the last layer. */
uint64_t first, n;
uint64_t last = start + count - 1;
trace_hbitmap_set(hb, start, count,
start >> hb->granularity, last >> hb->granularity);
first = start >> hb->granularity;
last >>= hb->granularity;
assert(last < hb->size);
n = last - first + 1;
hb->count += n - hb_count_between(hb, first, last);
if (hb_set_between(hb, HBITMAP_LEVELS - 1, first, last) &&
hb->meta) {
hbitmap_set(hb->meta, start, count);
}
}
/* Resetting works the other way round: propagate up if the new
* value is zero.
*/
static inline bool hb_reset_elem(unsigned long *elem, uint64_t start, uint64_t last)
{
unsigned long mask;
bool blanked;
assert((last >> BITS_PER_LEVEL) == (start >> BITS_PER_LEVEL));
assert(start <= last);
mask = 2UL << (last & (BITS_PER_LONG - 1));
mask -= 1UL << (start & (BITS_PER_LONG - 1));
blanked = *elem != 0 && ((*elem & ~mask) == 0);
*elem &= ~mask;
return blanked;
}
/* The recursive workhorse (the depth is limited to HBITMAP_LEVELS)...
* Returns true if at least one bit is changed. */
static bool hb_reset_between(HBitmap *hb, int level, uint64_t start,
uint64_t last)
{
size_t pos = start >> BITS_PER_LEVEL;
size_t lastpos = last >> BITS_PER_LEVEL;
bool changed = false;
size_t i;
i = pos;
if (i < lastpos) {
uint64_t next = (start | (BITS_PER_LONG - 1)) + 1;
/* Here we need a more complex test than when setting bits. Even if
* something was changed, we must not blank bits in the upper level
* unless the lower-level word became entirely zero. So, remove pos
* from the upper-level range if bits remain set.
*/
if (hb_reset_elem(&hb->levels[level][i], start, next - 1)) {
changed = true;
} else {
pos++;
}
for (;;) {
start = next;
next += BITS_PER_LONG;
if (++i == lastpos) {
break;
}
changed |= (hb->levels[level][i] != 0);
hb->levels[level][i] = 0UL;
}
}
/* Same as above, this time for lastpos. */
if (hb_reset_elem(&hb->levels[level][i], start, last)) {
changed = true;
} else {
lastpos--;
}
if (level > 0 && changed) {
hb_reset_between(hb, level - 1, pos, lastpos);
}
return changed;
}
void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count)
{
/* Compute range in the last layer. */
uint64_t first;
uint64_t last = start + count - 1;
trace_hbitmap_reset(hb, start, count,
start >> hb->granularity, last >> hb->granularity);
first = start >> hb->granularity;
last >>= hb->granularity;
assert(last < hb->size);
hb->count -= hb_count_between(hb, first, last);
if (hb_reset_between(hb, HBITMAP_LEVELS - 1, first, last) &&
hb->meta) {
hbitmap_set(hb->meta, start, count);
}
}
void hbitmap_reset_all(HBitmap *hb)
{
unsigned int i;
/* Same as hbitmap_alloc() except for memset() instead of malloc() */
for (i = HBITMAP_LEVELS; --i >= 1; ) {
memset(hb->levels[i], 0, hb->sizes[i] * sizeof(unsigned long));
}
hb->levels[0][0] = 1UL << (BITS_PER_LONG - 1);
hb->count = 0;
}
bool hbitmap_get(const HBitmap *hb, uint64_t item)
{
/* Compute position and bit in the last layer. */
uint64_t pos = item >> hb->granularity;
unsigned long bit = 1UL << (pos & (BITS_PER_LONG - 1));
assert(pos < hb->size);
return (hb->levels[HBITMAP_LEVELS - 1][pos >> BITS_PER_LEVEL] & bit) != 0;
}
uint64_t hbitmap_serialization_granularity(const HBitmap *hb)
{
/* Must hold true so that the shift below is defined
* (ld(64) == 6, i.e. 1 << 6 == 64) */
assert(hb->granularity < 64 - 6);
/* Require at least 64 bit granularity to be safe on both 64 bit and 32 bit
* hosts. */
return UINT64_C(64) << hb->granularity;
}
/* Start should be aligned to serialization granularity, chunk size should be
* aligned to serialization granularity too, except for last chunk.
*/
static void serialization_chunk(const HBitmap *hb,
uint64_t start, uint64_t count,
unsigned long **first_el, uint64_t *el_count)
{
uint64_t last = start + count - 1;
uint64_t gran = hbitmap_serialization_granularity(hb);
assert((start & (gran - 1)) == 0);
assert((last >> hb->granularity) < hb->size);
if ((last >> hb->granularity) != hb->size - 1) {
assert((count & (gran - 1)) == 0);
}
start = (start >> hb->granularity) >> BITS_PER_LEVEL;
last = (last >> hb->granularity) >> BITS_PER_LEVEL;
*first_el = &hb->levels[HBITMAP_LEVELS - 1][start];
*el_count = last - start + 1;
}
uint64_t hbitmap_serialization_size(const HBitmap *hb,
uint64_t start, uint64_t count)
{
uint64_t el_count;
unsigned long *cur;
if (!count) {
return 0;
}
serialization_chunk(hb, start, count, &cur, &el_count);
return el_count * sizeof(unsigned long);
}
void hbitmap_serialize_part(const HBitmap *hb, uint8_t *buf,
uint64_t start, uint64_t count)
{
uint64_t el_count;
unsigned long *cur, *end;
if (!count) {
return;
}
serialization_chunk(hb, start, count, &cur, &el_count);
end = cur + el_count;
while (cur != end) {
unsigned long el =
(BITS_PER_LONG == 32 ? cpu_to_le32(*cur) : cpu_to_le64(*cur));
memcpy(buf, &el, sizeof(el));
buf += sizeof(el);
cur++;
}
}
void hbitmap_deserialize_part(HBitmap *hb, uint8_t *buf,
uint64_t start, uint64_t count,
bool finish)
{
uint64_t el_count;
unsigned long *cur, *end;
if (!count) {
return;
}
serialization_chunk(hb, start, count, &cur, &el_count);
end = cur + el_count;
while (cur != end) {
memcpy(cur, buf, sizeof(*cur));
if (BITS_PER_LONG == 32) {
le32_to_cpus((uint32_t *)cur);
} else {
le64_to_cpus((uint64_t *)cur);
}
buf += sizeof(unsigned long);
cur++;
}
if (finish) {
hbitmap_deserialize_finish(hb);
}
}
void hbitmap_deserialize_zeroes(HBitmap *hb, uint64_t start, uint64_t count,
bool finish)
{
uint64_t el_count;
unsigned long *first;
if (!count) {
return;
}
serialization_chunk(hb, start, count, &first, &el_count);
memset(first, 0, el_count * sizeof(unsigned long));
if (finish) {
hbitmap_deserialize_finish(hb);
}
}
void hbitmap_deserialize_finish(HBitmap *bitmap)
{
int64_t i, size, prev_size;
int lev;
/* restore levels starting from penultimate to zero level, assuming
* that the last level is ok */
size = MAX((bitmap->size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
for (lev = HBITMAP_LEVELS - 1; lev-- > 0; ) {
prev_size = size;
size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
memset(bitmap->levels[lev], 0, size * sizeof(unsigned long));
for (i = 0; i < prev_size; ++i) {
if (bitmap->levels[lev + 1][i]) {
bitmap->levels[lev][i >> BITS_PER_LEVEL] |=
1UL << (i & (BITS_PER_LONG - 1));
}
}
}
bitmap->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
}
void hbitmap_free(HBitmap *hb)
{
unsigned i;
assert(!hb->meta);
for (i = HBITMAP_LEVELS; i-- > 0; ) {
g_free(hb->levels[i]);
}
g_free(hb);
}
HBitmap *hbitmap_alloc(uint64_t size, int granularity)
{
HBitmap *hb = g_new0(struct HBitmap, 1);
unsigned i;
assert(granularity >= 0 && granularity < 64);
size = (size + (1ULL << granularity) - 1) >> granularity;
assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
hb->size = size;
hb->granularity = granularity;
for (i = HBITMAP_LEVELS; i-- > 0; ) {
size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
hb->sizes[i] = size;
hb->levels[i] = g_new0(unsigned long, size);
}
/* We necessarily have free bits in level 0 due to the definition
* of HBITMAP_LEVELS, so use one for a sentinel. This speeds up
* hbitmap_iter_skip_words.
*/
assert(size == 1);
hb->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
return hb;
}
void hbitmap_truncate(HBitmap *hb, uint64_t size)
{
bool shrink;
unsigned i;
uint64_t num_elements = size;
uint64_t old;
/* Size comes in as logical elements, adjust for granularity. */
size = (size + (1ULL << hb->granularity) - 1) >> hb->granularity;
assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
shrink = size < hb->size;
/* bit sizes are identical; nothing to do. */
if (size == hb->size) {
return;
}
/* If we're losing bits, let's clear those bits before we invalidate all of
* our invariants. This helps keep the bitcount consistent, and will prevent
* us from carrying around garbage bits beyond the end of the map.
*/
if (shrink) {
/* Don't clear partial granularity groups;
* start at the first full one. */
uint64_t start = ROUND_UP(num_elements, UINT64_C(1) << hb->granularity);
uint64_t fix_count = (hb->size << hb->granularity) - start;
assert(fix_count);
hbitmap_reset(hb, start, fix_count);
}
hb->size = size;
for (i = HBITMAP_LEVELS; i-- > 0; ) {
size = MAX(BITS_TO_LONGS(size), 1);
if (hb->sizes[i] == size) {
break;
}
old = hb->sizes[i];
hb->sizes[i] = size;
hb->levels[i] = g_realloc(hb->levels[i], size * sizeof(unsigned long));
if (!shrink) {
memset(&hb->levels[i][old], 0x00,
(size - old) * sizeof(*hb->levels[i]));
}
}
if (hb->meta) {
hbitmap_truncate(hb->meta, hb->size << hb->granularity);
}
}
/**
* Given HBitmaps A and B, let A := A (BITOR) B.
* Bitmap B will not be modified.
*
* @return true if the merge was successful,
* false if it was not attempted.
*/
bool hbitmap_merge(HBitmap *a, const HBitmap *b)
{
int i;
uint64_t j;
if ((a->size != b->size) || (a->granularity != b->granularity)) {
return false;
}
if (hbitmap_count(b) == 0) {
return true;
}
/* This merge is O(size), as BITS_PER_LONG and HBITMAP_LEVELS are constant.
* It may be possible to improve running times for sparsely populated maps
* by using hbitmap_iter_next, but this is suboptimal for dense maps.
*/
for (i = HBITMAP_LEVELS - 1; i >= 0; i--) {
for (j = 0; j < a->sizes[i]; j++) {
a->levels[i][j] |= b->levels[i][j];
}
}
return true;
}
HBitmap *hbitmap_create_meta(HBitmap *hb, int chunk_size)
{
assert(!(chunk_size & (chunk_size - 1)));
assert(!hb->meta);
hb->meta = hbitmap_alloc(hb->size << hb->granularity,
hb->granularity + ctz32(chunk_size));
return hb->meta;
}
void hbitmap_free_meta(HBitmap *hb)
{
assert(hb->meta);
hbitmap_free(hb->meta);
hb->meta = NULL;
}