dm vdo: add the compressed block bin packer

When blocks do not deduplicate, vdo will attempt to compress them. Up to 14
compressed blocks may be packed into a single data block (this limitation
is imposed by the block map). The packer implements a simple best-fit
packing algorithm and also manages the formatting and writing of compressed
blocks when bins fill.
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/packer.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef VDO_PACKER_H
+#define VDO_PACKER_H
+
+#include <linux/list.h>
+
+#include "admin-state.h"
+#include "constants.h"
+#include "encodings.h"
+#include "statistics.h"
+#include "types.h"
+#include "wait-queue.h"
+
+enum {
+	DEFAULT_PACKER_BINS = 16,
+};
+
+/* The header of a compressed block. */
+struct compressed_block_header {
+	/* Unsigned 32-bit major and minor versions, little-endian */
+	struct packed_version_number version;
+
+	/* List of unsigned 16-bit compressed block sizes, little-endian */
+	__le16 sizes[VDO_MAX_COMPRESSION_SLOTS];
+} __packed;
+
+enum {
+	VDO_COMPRESSED_BLOCK_DATA_SIZE = VDO_BLOCK_SIZE - sizeof(struct compressed_block_header),
+
+	/*
+	 * A compressed block is only written if we can pack at least two fragments into it, so a
+	 * fragment which fills the entire data portion of a compressed block is too big.
+	 */
+	VDO_MAX_COMPRESSED_FRAGMENT_SIZE = VDO_COMPRESSED_BLOCK_DATA_SIZE - 1,
+};
+
+/* * The compressed block overlay. */
+struct compressed_block {
+	struct compressed_block_header header;
+	char data[VDO_COMPRESSED_BLOCK_DATA_SIZE];
+} __packed;
+
+/*
+ * Each packer_bin holds an incomplete batch of data_vios that only partially fill a compressed
+ * block. The bins are kept in a ring sorted by the amount of unused space so the first bin with
+ * enough space to hold a newly-compressed data_vio can easily be found. When the bin fills up or
+ * is flushed, the first uncanceled data_vio in the bin is selected to be the agent for that bin.
+ * Upon entering the packer, each data_vio already has its compressed data in the first slot of the
+ * data_vio's compressed_block (overlaid on the data_vio's scratch_block). So the agent's fragment
+ * is already in place. The fragments for the other uncanceled data_vios in the bin are packed into
+ * the agent's compressed block. The agent then writes out the compressed block. If the write is
+ * successful, the agent shares its pbn lock which each of the other data_vios in its compressed
+ * block and sends each on its way. Finally the agent itself continues on the write path as before.
+ *
+ * There is one special bin which is used to hold data_vios which have been canceled and removed
+ * from their bin by the packer. These data_vios need to wait for the canceller to rendezvous with
+ * them (VDO-2809) and so they sit in this special bin.
+ */
+struct packer_bin {
+	/* List links for packer.packer_bins */
+	struct list_head list;
+	/* The number of items in the bin */
+	slot_number_t slots_used;
+	/* The number of compressed block bytes remaining in the current batch */
+	size_t free_space;
+	/* The current partial batch of data_vios, waiting for more */
+	struct data_vio *incoming[];
+};
+
+struct packer {
+	/* The ID of the packer's callback thread */
+	thread_id_t thread_id;
+	/* The number of bins */
+	block_count_t size;
+	/* A list of all packer_bins, kept sorted by free_space */
+	struct list_head bins;
+	/*
+	 * A bin to hold data_vios which were canceled out of the packer and are waiting to
+	 * rendezvous with the canceling data_vio.
+	 */
+	struct packer_bin *canceled_bin;
+
+	/* The current flush generation */
+	sequence_number_t flush_generation;
+
+	/* The administrative state of the packer */
+	struct admin_state state;
+
+	/* Statistics are only updated on the packer thread, but are accessed from other threads */
+	struct packer_statistics statistics;
+};
+
+int vdo_get_compressed_block_fragment(enum block_mapping_state mapping_state,
+				      struct compressed_block *block,
+				      u16 *fragment_offset, u16 *fragment_size);
+
+int __must_check vdo_make_packer(struct vdo *vdo, block_count_t bin_count,
+				 struct packer **packer_ptr);
+
+void vdo_free_packer(struct packer *packer);
+
+struct packer_statistics __must_check vdo_get_packer_statistics(const struct packer *packer);
+
+void vdo_attempt_packing(struct data_vio *data_vio);
+
+void vdo_flush_packer(struct packer *packer);
+
+void vdo_remove_lock_holder_from_packer(struct vdo_completion *completion);
+
+void vdo_increment_packer_flush_generation(struct packer *packer);
+
+void vdo_drain_packer(struct packer *packer, struct vdo_completion *completion);
+
+void vdo_resume_packer(struct packer *packer, struct vdo_completion *parent);
+
+void vdo_dump_packer(const struct packer *packer);
+
+#endif /* VDO_PACKER_H */