[Qemu-devel] [PATCH RFC v2 22/22] block/pcache: drop used pcache node

[Pavel Butsykin]

The pcache is directed to certain situations to sequential reads.
This concept allows to drop parts of the cache that were already used, which
will reduce the size of cache and the number of displaced nodes.

Signed-off-by: Pavel Butsykin <address@hidden>
---
 block/pcache.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/block/pcache.c b/block/pcache.c
index 2b2edf5..3fad4ca 100644
--- a/block/pcache.c
+++ b/block/pcache.c
@@ -88,6 +88,7 @@ typedef struct PCNode {
     uint32_t                 status;
     uint32_t                 ref;
     uint8_t                  *data;
+    uint32_t                 rdcnt;
     CoMutex                  lock;
 } PCNode;
 
@@ -342,6 +343,7 @@ static inline void *pcache_node_alloc(RbNodeKey* key)
     node->cm.nb_sectors = key->size;
     node->ref = 0;
     node->status = NODE_WAIT_STATUS;
+    node->rdcnt = 0;
     qemu_co_mutex_init(&node->lock);
     node->data = g_malloc(node->cm.nb_sectors << BDRV_SECTOR_BITS);
     node->wait.cnt = 0;
@@ -560,11 +562,23 @@ static void pcache_node_rw_buf(PrefCacheAIOCB *acb, 
PCNode* node, uint32_t type)
                                node->cm.sector_num, node->cm.nb_sectors)
            << BDRV_SECTOR_BITS;
 
-    qemu_co_mutex_lock(&node->lock); /* XXX: use rw lock */
-    copy = type & NODE_READ_BUF ?
-        qemu_iovec_from_buf(acb->qiov, qiov_offs, node->data + node_offs, size)
-        : qemu_iovec_to_buf(acb->qiov, qiov_offs, node->data + node_offs, 
size);
-    qemu_co_mutex_unlock(&node->lock);
+    if (type & NODE_READ_BUF) {
+        qemu_co_mutex_lock(&node->lock); /* XXX: use rw lock */
+        copy = qemu_iovec_from_buf(acb->qiov, qiov_offs,
+                                   node->data + node_offs, size);
+        qemu_co_mutex_unlock(&node->lock);
+
+        /* pcache node is no longer needed, when it was all read */
+        atomic_add(&node->rdcnt, size >> BDRV_SECTOR_BITS);
+        if (node->rdcnt >= node->cm.nb_sectors) {
+            pcache_node_drop(acb->s, node);
+        }
+    } else {
+        qemu_co_mutex_lock(&node->lock); /* XXX: use rw lock */
+        copy = qemu_iovec_to_buf(acb->qiov, qiov_offs,
+                                 node->data + node_offs, size);
+        qemu_co_mutex_unlock(&node->lock);
+    }
     assert(copy == size);
 }
 
-- 
2.8.3