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>

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 1d25147392a5a0818a8a773c8f5d995e68e5bb93..75746a7f43a7cecd97285aaa620abca7feddd833 100644 (file)
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -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);
+}

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 168fc32e7b31936b413e99b0adf5b678ccce59a2..8c17c0e3aaf3457565323e32c5cb2cfb9b802370 100644 (file)
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -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);
+            }
         }
     }
 

diff --git a/block/qcow2.h b/block/qcow2.h
index 96a8d43c1721197ff567cb0b293b26aeccca9311..52c374e9ed6c66eb161869da31b09c5786ce2d6e 100644 (file)
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -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,