path: root/drivers/md/raid5-ppl.c

/*
 * Partial Parity Log for closing the RAID5 write hole
 * Copyright (c) 2017, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */

#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/crc32c.h>
#include <linux/flex_array.h>
#include <linux/async_tx.h>
#include <linux/raid/md_p.h>
#include "md.h"
#include "raid5.h"

/*
 * PPL consists of a 4KB header (struct ppl_header) and at least 128KB for
 * partial parity data. The header contains an array of entries
 * (struct ppl_header_entry) which describe the logged write requests.
 * Partial parity for the entries comes after the header, written in the same
 * sequence as the entries:
 *
 * Header
 *   entry0
 *   ...
 *   entryN
 * PP data
 *   PP for entry0
 *   ...
 *   PP for entryN
 *
 * An entry describes one or more consecutive stripe_heads, up to a full
 * stripe. The modifed raid data chunks form an m-by-n matrix, where m is the
 * number of stripe_heads in the entry and n is the number of modified data
 * disks. Every stripe_head in the entry must write to the same data disks.
 * An example of a valid case described by a single entry (writes to the first
 * stripe of a 4 disk array, 16k chunk size):
 *
 * sh->sector   dd0   dd1   dd2    ppl
 *            +-----+-----+-----+
 * 0          | --- | --- | --- | +----+
 * 8          | -W- | -W- | --- | | pp |   data_sector = 8
 * 16         | -W- | -W- | --- | | pp |   data_size = 3 * 2 * 4k
 * 24         | -W- | -W- | --- | | pp |   pp_size = 3 * 4k
 *            +-----+-----+-----+ +----+
 *
 * data_sector is the first raid sector of the modified data, data_size is the
 * total size of modified data and pp_size is the size of partial parity for
 * this entry. Entries for full stripe writes contain no partial parity
 * (pp_size = 0), they only mark the stripes for which parity should be
 * recalculated after an unclean shutdown. Every entry holds a checksum of its
 * partial parity, the header also has a checksum of the header itself.
 *
 * A write request is always logged to the PPL instance stored on the parity
 * disk of the corresponding stripe. For each member disk there is one ppl_log
 * used to handle logging for this disk, independently from others. They are
 * grouped in child_logs array in struct ppl_conf, which is assigned to
 * r5conf->log_private.
 *
 * ppl_io_unit represents a full PPL write, header_page contains the ppl_header.
 * PPL entries for logged stripes are added in ppl_log_stripe(). A stripe_head
 * can be appended to the last entry if it meets the conditions for a valid
 * entry described above, otherwise a new entry is added. Checksums of entries
 * are calculated incrementally as stripes containing partial parity are being
 * added. ppl_submit_iounit() calculates the checksum of the header and submits
 * a bio containing the header page and partial parity pages (sh->ppl_page) for
 * all stripes of the io_unit. When the PPL write completes, the stripes
 * associated with the io_unit are released and raid5d starts writing their data
 * and parity. When all stripes are written, the io_unit is freed and the next
 * can be submitted.
 *
 * An io_unit is used to gather stripes until it is submitted or becomes full
 * (if the maximum number of entries or size of PPL is reached). Another io_unit
 * can't be submitted until the previous has completed (PPL and stripe
 * data+parity is written). The log->io_list tracks all io_units of a log
 * (for a single member disk). New io_units are added to the end of the list
 * and the first io_unit is submitted, if it is not submitted already.
 * The current io_unit accepting new stripes is always at the end of the list.
 */

struct ppl_conf {
	struct mddev *mddev;

	/* array of child logs, one for each raid disk */
	struct ppl_log *child_logs;
	int count;

	int block_size;		/* the logical block size used for data_sector
				 * in ppl_header_entry */
	u32 signature;		/* raid array identifier */
	atomic64_t seq;		/* current log write sequence number */

	struct kmem_cache *io_kc;
	mempool_t *io_pool;
	struct bio_set *bs;
	mempool_t *meta_pool;

	/* used only for recovery */
	int recovered_entries;
	int mismatch_count;

	/* stripes to retry if failed to allocate io_unit */
	struct list_head no_mem_stripes;
	spinlock_t no_mem_stripes_lock;
};

struct ppl_log {
	struct ppl_conf *ppl_conf;	/* shared between all log instances */

	struct md_rdev *rdev;		/* array member disk associated with
					 * this log instance */
	struct mutex io_mutex;
	struct ppl_io_unit *current_io;	/* current io_unit accepting new data
					 * always at the end of io_list */
	spinlock_t io_list_lock;
	struct list_head io_list;	/* all io_units of this log */
};

#define PPL_IO_INLINE_BVECS 32

struct ppl_io_unit {
	struct ppl_log *log;

	struct page *header_page;	/* for ppl_header */

	unsigned int entries_count;	/* number of entries in ppl_header */
	unsigned int pp_size;		/* total size current of partial parity */

	u64 seq;			/* sequence number of this log write */
	struct list_head log_sibling;	/* log->io_list */

	struct list_head stripe_list;	/* stripes added to the io_unit */
	atomic_t pending_stripes;	/* how many stripes not written to raid */

	bool submitted;			/* true if write to log started */

	/* inline bio and its biovec for submitting the iounit */
	struct bio bio;
	struct bio_vec biovec[PPL_IO_INLINE_BVECS];
};

struct dma_async_tx_descriptor *
ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
		       struct dma_async_tx_descriptor *tx)
{
	int disks = sh->disks;
	struct page **xor_srcs = flex_array_get(percpu->scribble, 0);
	int count = 0, pd_idx = sh->