}
/*
- * Lookup a metadata block in the rbtree.
+ * Lookup a metadata block in the rbtree. If the block is found, increment
+ * its reference count.
*/
-static struct dmz_mblock *dmz_lookup_mblock(struct dmz_metadata *zmd,
- sector_t mblk_no)
+static struct dmz_mblock *dmz_get_mblock_fast(struct dmz_metadata *zmd,
+ sector_t mblk_no)
{
struct rb_root *root = &zmd->mblk_rbtree;
struct rb_node *node = root->rb_node;
while (node) {
mblk = container_of(node, struct dmz_mblock, node);
- if (mblk->no == mblk_no)
+ if (mblk->no == mblk_no) {
+ /*
+ * If this is the first reference to the block,
+ * remove it from the LRU list.
+ */
+ mblk->ref++;
+ if (mblk->ref == 1 &&
+ !test_bit(DMZ_META_DIRTY, &mblk->state))
+ list_del_init(&mblk->link);
return mblk;
+ }
node = (mblk->no < mblk_no) ? node->rb_left : node->rb_right;
}
}
/*
- * Read a metadata block from disk.
+ * Read an uncached metadata block from disk and add it to the cache.
*/
-static struct dmz_mblock *dmz_fetch_mblock(struct dmz_metadata *zmd,
- sector_t mblk_no)
+static struct dmz_mblock *dmz_get_mblock_slow(struct dmz_metadata *zmd,
+ sector_t mblk_no)
{
- struct dmz_mblock *mblk;
+ struct dmz_mblock *mblk, *m;
sector_t block = zmd->sb[zmd->mblk_primary].block + mblk_no;
struct bio *bio;
- /* Get block and insert it */
+ /* Get a new block and a BIO to read it */
mblk = dmz_alloc_mblock(zmd, mblk_no);
if (!mblk)
return NULL;
- spin_lock(&zmd->mblk_lock);
- mblk->ref++;
- set_bit(DMZ_META_READING, &mblk->state);
- dmz_insert_mblock(zmd, mblk);
- spin_unlock(&zmd->mblk_lock);
-
bio = bio_alloc(GFP_NOIO, 1);
if (!bio) {
dmz_free_mblock(zmd, mblk);
return NULL;
}
+ spin_lock(&zmd->mblk_lock);
+
+ /*
+ * Make sure that another context did not start reading
+ * the block already.
+ */
+ m = dmz_get_mblock_fast(zmd, mblk_no);
+ if (m) {
+ spin_unlock(&zmd->mblk_lock);
+ dmz_free_mblock(zmd, mblk);
+ bio_put(bio);
+ return m;
+ }
+
+ mblk->ref++;
+ set_bit(DMZ_META_READING, &mblk->state);
+ dmz_insert_mblock(zmd, mblk);
+
+ spin_unlock(&zmd->mblk_lock);
+
+ /* Submit read BIO */
bio->bi_iter.bi_sector = dmz_blk2sect(block);
bio_set_dev(bio, zmd->dev->bdev);
bio->bi_private = mblk;
/* Check rbtree */
spin_lock(&zmd->mblk_lock);
- mblk = dmz_lookup_mblock(zmd, mblk_no);
- if (mblk) {
- /* Cache hit: remove block from LRU list */
- mblk->ref++;
- if (mblk->ref == 1 &&
- !test_bit(DMZ_META_DIRTY, &mblk->state))
- list_del_init(&mblk->link);
- }
+ mblk = dmz_get_mblock_fast(zmd, mblk_no);
spin_unlock(&zmd->mblk_lock);
if (!mblk) {
/* Cache miss: read the block from disk */
- mblk = dmz_fetch_mblock(zmd, mblk_no);
+ mblk = dmz_get_mblock_slow(zmd, mblk_no);
if (!mblk)
return ERR_PTR(-ENOMEM);
}