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HBitmap: Introduce "meta" bitmap to track bit changes 

Upon each bit toggle, the corresponding bit in the meta bitmap will be
set.

Signed-off-by: Fam Zheng <famz@redhat.com>
[Amended text inline. --js]
Reviewed-by: Max Reitz <mreitz@redhat.com>

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1476395910-8697-3-git-send-email-jsnow@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Fam Zheng 2016-10-13 17:58:22 -04:00 committed by Max Reitz
parent dc162c8e4f
commit 07ac4cdb57
2 changed files with 75 additions and 15 deletions
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21
include/qemu/hbitmap.h
View File

@ -178,6 +178,27 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first);
*/
unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
/* hbitmap_create_meta:
* Create a "meta" hbitmap to track dirtiness of the bits in this HBitmap.
* The caller owns the created bitmap and must call hbitmap_free_meta(hb) to
* free it.
*
* Currently, we only guarantee that if a bit in the hbitmap is changed it
* will be reflected in the meta bitmap, but we do not yet guarantee the
* opposite.
*
* @hb: The HBitmap to operate on.
* @chunk_size: How many bits in @hb does one bit in the meta track.
*/
HBitmap *hbitmap_create_meta(HBitmap *hb, int chunk_size);
/* hbitmap_free_meta:
* Free the meta bitmap of @hb.
*
* @hb: The HBitmap whose meta bitmap should be freed.
*/
void hbitmap_free_meta(HBitmap *hb);
/**
* hbitmap_iter_next:
* @hbi: HBitmapIter to operate on.

69
util/hbitmap.c
View File

@ -78,6 +78,9 @@ struct HBitmap {
*/
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
@ -209,25 +212,27 @@ static uint64_t hb_count_between(HBitmap *hb, uint64_t start, uint64_t last)
}
/* Setting starts at the last layer and propagates up if an element
* changes from zero to non-zero.
* changes.
*/
static inline bool hb_set_elem(unsigned long *elem, uint64_t start, uint64_t last)
{
unsigned long mask;
bool changed;
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));
changed = (*elem == 0);
old = *elem;
*elem |= mask;
return changed;
return old != *elem;
}
/* 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)
/* 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;
@ -256,23 +261,28 @@ static void hb_set_between(HBitmap *hb, int level, uint64_t start, uint64_t last
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);
start >>= hb->granularity;
first = start >> hb->granularity;
last >>= hb->granularity;
count = last - start + 1;
assert(last < hb->size);
n = last - first + 1;
hb->count += count - hb_count_between(hb, start, last);
hb_set_between(hb, HBITMAP_LEVELS - 1, start, last);
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
@ -293,8 +303,10 @@ static inline bool hb_reset_elem(unsigned long *elem, uint64_t start, uint64_t l
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)
/* 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;
@ -337,22 +349,29 @@ static void hb_reset_between(HBitmap *hb, int level, uint64_t start, uint64_t la
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);
start >>= hb->granularity;
first = start >> hb->granularity;
last >>= hb->granularity;
assert(last < hb->size);
hb->count -= hb_count_between(hb, start, last);
hb_reset_between(hb, HBITMAP_LEVELS - 1, start, last);
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)
@ -381,6 +400,7 @@ bool hbitmap_get(const HBitmap *hb, uint64_t item)
void hbitmap_free(HBitmap *hb)
{
unsigned i;
assert(!hb->meta);
for (i = HBITMAP_LEVELS; i-- > 0; ) {
g_free(hb->levels[i]);
}
@ -458,6 +478,9 @@ void hbitmap_truncate(HBitmap *hb, uint64_t size)
(size - old) * sizeof(*hb->levels[i]));
}
}
if (hb->meta) {
hbitmap_truncate(hb->meta, hb->size << hb->granularity);
}
}
@ -493,3 +516,19 @@ bool hbitmap_merge(HBitmap *a, const HBitmap *b)
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;
}