dm vdo: implement the block map page cache

The set of leaf pages of the block map tree is too large to fit in memory,
so each block map zone maintains a cache of leaf pages. This patch adds the
implementation of that cache.
Co-developed-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: J. corwin Coburn <corwin@hurlbutnet.net>
Co-developed-by: Michael Sclafani <dm-devel@lists.linux.dev>
Signed-off-by: Michael Sclafani <dm-devel@lists.linux.dev>
Co-developed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-vdo/block-map.h

@@ -30,6 +30,140 @@ typedef u32 vdo_page_generation;
 
 extern const struct block_map_entry UNMAPPED_BLOCK_MAP_ENTRY;
 
+/* The VDO Page Cache abstraction. */
+struct vdo_page_cache {
+	/* the VDO which owns this cache */
+	struct vdo *vdo;
+	/* number of pages in cache */
+	page_count_t page_count;
+	/* number of pages to write in the current batch */
+	page_count_t pages_in_batch;
+	/* Whether the VDO is doing a read-only rebuild */
+	bool rebuilding;
+
+	/* array of page information entries */
+	struct page_info *infos;
+	/* raw memory for pages */
+	char *pages;
+	/* cache last found page info */
+	struct page_info *last_found;
+	/* map of page number to info */
+	struct int_map *page_map;
+	/* main LRU list (all infos) */
+	struct list_head lru_list;
+	/* free page list (oldest first) */
+	struct list_head free_list;
+	/* outgoing page list */
+	struct list_head outgoing_list;
+	/* number of read I/O operations pending */
+	page_count_t outstanding_reads;
+	/* number of write I/O operations pending */
+	page_count_t outstanding_writes;
+	/* number of pages covered by the current flush */
+	page_count_t pages_in_flush;
+	/* number of pages waiting to be included in the next flush */
+	page_count_t pages_to_flush;
+	/* number of discards in progress */
+	unsigned int discard_count;
+	/* how many VPCs waiting for free page */
+	unsigned int waiter_count;
+	/* queue of waiters who want a free page */
+	struct wait_queue free_waiters;
+	/*
+	 * Statistics are only updated on the logical zone thread, but are accessed from other
+	 * threads.
+	 */
+	struct block_map_statistics stats;
+	/* counter for pressure reports */
+	u32 pressure_report;
+	/* the block map zone to which this cache belongs */
+	struct block_map_zone *zone;
+};
+
+/*
+ * The state of a page buffer. If the page buffer is free no particular page is bound to it,
+ * otherwise the page buffer is bound to particular page whose absolute pbn is in the pbn field. If
+ * the page is resident or dirty the page data is stable and may be accessed. Otherwise the page is
+ * in flight (incoming or outgoing) and its data should not be accessed.
+ *
+ * @note Update the static data in get_page_state_name() if you change this enumeration.
+ */
+enum vdo_page_buffer_state {
+	/* this page buffer is not being used */
+	PS_FREE,
+	/* this page is being read from store */
+	PS_INCOMING,
+	/* attempt to load this page failed */
+	PS_FAILED,
+	/* this page is valid and un-modified */
+	PS_RESIDENT,
+	/* this page is valid and modified */
+	PS_DIRTY,
+	/* this page is being written and should not be used */
+	PS_OUTGOING,
+	/* not a state */
+	PAGE_STATE_COUNT,
+} __packed;
+
+/*
+ * The write status of page
+ */
+enum vdo_page_write_status {
+	WRITE_STATUS_NORMAL,
+	WRITE_STATUS_DISCARD,
+	WRITE_STATUS_DEFERRED,
+} __packed;
+
+/* Per-page-slot information. */
+struct page_info {
+	/* Preallocated page struct vio */
+	struct vio *vio;
+	/* back-link for references */
+	struct vdo_page_cache *cache;
+	/* the pbn of the page */
+	physical_block_number_t pbn;
+	/* page is busy (temporarily locked) */
+	u16 busy;
+	/* the write status the page */
+	enum vdo_page_write_status write_status;
+	/* page state */
+	enum vdo_page_buffer_state state;
+	/* queue of completions awaiting this item */
+	struct wait_queue waiting;
+	/* state linked list entry */
+	struct list_head state_entry;
+	/* LRU entry */
+	struct list_head lru_entry;
+	/*
+	 * The earliest recovery journal block containing uncommitted updates to the block map page
+	 * associated with this page_info. A reference (lock) is held on that block to prevent it
+	 * from being reaped. When this value changes, the reference on the old value must be
+	 * released and a reference on the new value must be acquired.
+	 */
+	sequence_number_t recovery_lock;
+};
+
+/*
+ * A completion awaiting a specific page. Also a live reference into the page once completed, until
+ * freed.
+ */
+struct vdo_page_completion {
+	/* The generic completion */
+	struct vdo_completion completion;
+	/* The cache involved */
+	struct vdo_page_cache *cache;
+	/* The waiter for the pending list */
+	struct waiter waiter;
+	/* The absolute physical block number of the page on disk */
+	physical_block_number_t pbn;
+	/* Whether the page may be modified */
+	bool writable;
+	/* Whether the page is available */
+	bool ready;
+	/* The info structure for the page, only valid when ready */
+	struct page_info *info;
+};
+
 struct forest;
 
 struct tree_page {
@@ -141,6 +275,26 @@ struct block_map {
 typedef int (*vdo_entry_callback_fn)(physical_block_number_t pbn,
 				     struct vdo_completion *completion);
 
+static inline struct vdo_page_completion *as_vdo_page_completion(struct vdo_completion *completion)
+{
+	vdo_assert_completion_type(completion, VDO_PAGE_COMPLETION);
+	return container_of(completion, struct vdo_page_completion, completion);
+}
+
+void vdo_release_page_completion(struct vdo_completion *completion);
+
+void vdo_get_page(struct vdo_page_completion *page_completion,
+		  struct block_map_zone *zone, physical_block_number_t pbn,
+		  bool writable, void *parent, vdo_action_fn callback,
+		  vdo_action_fn error_handler, bool requeue);
+
+void vdo_request_page_write(struct vdo_completion *completion);
+
+int __must_check vdo_get_cached_page(struct vdo_completion *completion,
+				     struct block_map_page **page_ptr);
+
+int __must_check vdo_invalidate_page_cache(struct vdo_page_cache *cache);
+
 static inline struct block_map_page * __must_check
 vdo_as_block_map_page(struct tree_page *tree_page)
 {