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qcow2: add qcow2_cache_discard 

Whenever l2/refcount table clusters are discarded from the file we can
automatically drop unnecessary content of the cache tables. This reduces
the chance of eviction useful cache data and eliminates inconsistent data
in the cache with the data in the file.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20170918124230.8152-3-pbutsykin@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Pavel Butsykin 2017-09-18 15:42:28 +03:00 committed by Max Reitz
parent 4ffca8904a
commit f71c08ea8e
3 changed files with 47 additions and 2 deletions
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26
block/qcow2-cache.c
View File

@ -411,3 +411,29 @@ void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c,
assert(c->entries[i].offset != 0);
c->entries[i].dirty = true;
}
void *qcow2_cache_is_table_offset(BlockDriverState *bs, Qcow2Cache *c,
uint64_t offset)
{
int i;
for (i = 0; i < c->size; i++) {
if (c->entries[i].offset == offset) {
return qcow2_cache_get_table_addr(bs, c, i);
}
}
return NULL;
}
void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, void *table)
{
int i = qcow2_cache_get_table_idx(bs, c, table);
assert(c->entries[i].ref == 0);
c->entries[i].offset = 0;
c->entries[i].lru_counter = 0;
c->entries[i].dirty = false;
qcow2_cache_table_release(bs, c, i, 1);
}

20
block/qcow2-refcount.c
View File

@ -861,8 +861,24 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
}
s->set_refcount(refcount_block, block_index, refcount);
if (refcount == 0 && s->discard_passthrough[type]) {
update_refcount_discard(bs, cluster_offset, s->cluster_size);
if (refcount == 0) {
void *table;
table = qcow2_cache_is_table_offset(bs, s->refcount_block_cache,
offset);
if (table != NULL) {
qcow2_cache_put(bs, s->refcount_block_cache, &refcount_block);
qcow2_cache_discard(bs, s->refcount_block_cache, table);
}
table = qcow2_cache_is_table_offset(bs, s->l2_table_cache, offset);
if (table != NULL) {
qcow2_cache_discard(bs, s->l2_table_cache, table);
}
if (s->discard_passthrough[type]) {
update_refcount_discard(bs, cluster_offset, s->cluster_size);
}
}
}

3
block/qcow2.h
View File

@ -649,6 +649,9 @@ int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
void **table);
void qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table);
void *qcow2_cache_is_table_offset(BlockDriverState *bs, Qcow2Cache *c,
uint64_t offset);
void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, void *table);
/* qcow2-bitmap.c functions */
int qcow2_check_bitmaps_refcounts(BlockDriverState *bs, BdrvCheckResult *res,