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qcow2: add qcow2_cache_discard

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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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20
block/qcow2-refcount.c
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@ -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);
}
}
}