linux/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 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 */