--- /dev/null
+/*
+ * 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 <string.h>
+#include <glib.h>
+#include <assert.h>
+#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 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 from zero to non-zero.
+ */
+static inline bool hb_set_elem(unsigned long *elem, uint64_t start, uint64_t last)
+{
+ unsigned long mask;
+ bool changed;
+
+ 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));
+ changed = (*elem == 0);
+ *elem |= mask;
+ return changed;
+}
+
+/* The recursive workhorse (the depth is limited to HBITMAP_LEVELS)... */
+static void 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);
+ }
+}
+
+void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t count)
+{
+ /* Compute range in the last layer. */
+ uint64_t last = start + count - 1;
+
+ trace_hbitmap_set(hb, start, count,
+ start >> hb->granularity, last >> hb->granularity);
+
+ start >>= hb->granularity;
+ last >>= hb->granularity;
+ count = last - start + 1;
+
+ hb->count += count - hb_count_between(hb, start, last);
+ hb_set_between(hb, HBITMAP_LEVELS - 1, start, last);
+}
+
+/* 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)... */
+static void 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);
+ }
+}
+
+void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count)
+{
+ /* Compute range in the last layer. */
+ uint64_t last = start + count - 1;
+
+ trace_hbitmap_reset(hb, start, count,
+ start >> hb->granularity, last >> hb->granularity);
+
+ start >>= hb->granularity;
+ last >>= hb->granularity;
+
+ hb->count -= hb_count_between(hb, start, last);
+ hb_reset_between(hb, HBITMAP_LEVELS - 1, start, last);
+}
+
+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));
+
+ return (hb->levels[HBITMAP_LEVELS - 1][pos >> BITS_PER_LEVEL] & bit) != 0;
+}
+
+void hbitmap_free(HBitmap *hb)
+{
+ unsigned i;
+ 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 = QEMU_ALIGN_UP(num_elements, 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]));
+ }
+ }
+}
+
+
+/**
+ * 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;
+}
Code Review / kvmfornfv.git / blobdiff