PCACHE_CACHE_SUBTREE_SIZE
u32 max_bvecs = (PCACHE_CACHE_SUBTREE_SIZE >> PAGE_SHIFT) + 1;
n_subtrees = DIV_ROUND_UP(cache->dev_size << SECTOR_SHIFT, PCACHE_CACHE_SUBTREE_SIZE);
if (key->len > PCACHE_CACHE_SUBTREE_SIZE - (key->off & PCACHE_CACHE_SUBTREE_SIZE_MASK))
key->len = PCACHE_CACHE_SUBTREE_SIZE - (key->off & PCACHE_CACHE_SUBTREE_SIZE_MASK);
if (key->len > PCACHE_CACHE_SUBTREE_SIZE - (key->off & PCACHE_CACHE_SUBTREE_SIZE_MASK))
key->len = PCACHE_CACHE_SUBTREE_SIZE - (key->off & PCACHE_CACHE_SUBTREE_SIZE_MASK);