md/r5cache: State machine for raid5-cache write back mode
This patch adds state machine for raid5-cache. With log device, the raid456 array could operate in two different modes (r5c_journal_mode): - write-back (R5C_MODE_WRITE_BACK) - write-through (R5C_MODE_WRITE_THROUGH) Existing code of raid5-cache only has write-through mode. For write-back cache, it is necessary to extend the state machine. With write-back cache, every stripe could operate in two different phases: - caching - writing-out In caching phase, the stripe handles writes as: - write to journal - return IO In writing-out phase, the stripe behaviors as a stripe in write through mode R5C_MODE_WRITE_THROUGH. STRIPE_R5C_CACHING is added to sh->state to differentiate caching and writing-out phase. Please note: this is a "no-op" patch for raid5-cache write-through mode. The following detailed explanation is copied from the raid5-cache.c: /* * raid5 cache state machine * * With rhe RAID cache, each stripe works in two phases: * - caching phase * - writing-out phase * * These two phases are controlled by bit STRIPE_R5C_CACHING: * if STRIPE_R5C_CACHING == 0, the stripe is in writing-out phase * if STRIPE_R5C_CACHING == 1, the stripe is in caching phase * * When there is no journal, or the journal is in write-through mode, * the stripe is always in writing-out phase. * * For write-back journal, the stripe is sent to caching phase on write * (r5c_handle_stripe_dirtying). r5c_make_stripe_write_out() kicks off * the write-out phase by clearing STRIPE_R5C_CACHING. * * Stripes in caching phase do not write the raid disks. Instead, all * writes are committed from the log device. Therefore, a stripe in * caching phase handles writes as: * - write to log device * - return IO * * Stripes in writing-out phase handle writes as: * - calculate parity * - write pending data and parity to journal * - write data and parity to raid disks * - return IO for pending writes */ Signed-off-by: Song Liu <songliubraving@fb.com> Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
Song Liu
Shaohua Li
parent
937621c36e
commit
2ded370373
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@ -40,6 +40,47 @@
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*/
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#define R5L_POOL_SIZE 4
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/*
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* r5c journal modes of the array: write-back or write-through.
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* write-through mode has identical behavior as existing log only
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* implementation.
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*/
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enum r5c_journal_mode {
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R5C_JOURNAL_MODE_WRITE_THROUGH = 0,
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R5C_JOURNAL_MODE_WRITE_BACK = 1,
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};
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/*
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* raid5 cache state machine
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*
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* With rhe RAID cache, each stripe works in two phases:
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* - caching phase
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* - writing-out phase
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*
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* These two phases are controlled by bit STRIPE_R5C_CACHING:
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* if STRIPE_R5C_CACHING == 0, the stripe is in writing-out phase
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* if STRIPE_R5C_CACHING == 1, the stripe is in caching phase
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*
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* When there is no journal, or the journal is in write-through mode,
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* the stripe is always in writing-out phase.
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*
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* For write-back journal, the stripe is sent to caching phase on write
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* (r5c_try_caching_write). r5c_make_stripe_write_out() kicks off
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* the write-out phase by clearing STRIPE_R5C_CACHING.
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*
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* Stripes in caching phase do not write the raid disks. Instead, all
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* writes are committed from the log device. Therefore, a stripe in
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* caching phase handles writes as:
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* - write to log device
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* - return IO
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*
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* Stripes in writing-out phase handle writes as:
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* - calculate parity
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* - write pending data and parity to journal
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* - write data and parity to raid disks
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* - return IO for pending writes
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*/
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struct r5l_log {
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struct md_rdev *rdev;
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@ -96,6 +137,9 @@ struct r5l_log {
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spinlock_t no_space_stripes_lock;
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bool need_cache_flush;
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/* for r5c_cache */
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enum r5c_journal_mode r5c_journal_mode;
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};
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/*
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@ -133,6 +177,12 @@ enum r5l_io_unit_state {
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IO_UNIT_STRIPE_END = 3, /* stripes data finished writing to raid */
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};
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bool r5c_is_writeback(struct r5l_log *log)
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{
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return (log != NULL &&
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log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_BACK);
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}
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static sector_t r5l_ring_add(struct r5l_log *log, sector_t start, sector_t inc)
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{
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start += inc;
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@ -168,12 +218,51 @@ static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
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io->state = state;
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}
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/*
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* Put the stripe into writing-out phase by clearing STRIPE_R5C_CACHING.
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* This function should only be called in write-back mode.
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*/
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static void r5c_make_stripe_write_out(struct stripe_head *sh)
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{
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struct r5conf *conf = sh->raid_conf;
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struct r5l_log *log = conf->log;
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BUG_ON(!r5c_is_writeback(log));
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WARN_ON(!test_bit(STRIPE_R5C_CACHING, &sh->state));
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clear_bit(STRIPE_R5C_CACHING, &sh->state);
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}
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/*
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* Setting proper flags after writing (or flushing) data and/or parity to the
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* log device. This is called from r5l_log_endio() or r5l_log_flush_endio().
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*/
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static void r5c_finish_cache_stripe(struct stripe_head *sh)
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{
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struct r5l_log *log = sh->raid_conf->log;
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if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH) {
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BUG_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
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/*
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* Set R5_InJournal for parity dev[pd_idx]. This means
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* all data AND parity in the journal. For RAID 6, it is
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* NOT necessary to set the flag for dev[qd_idx], as the
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* two parities are written out together.
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*/
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set_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);
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} else
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BUG(); /* write-back logic in next patch */
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}
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static void r5l_io_run_stripes(struct r5l_io_unit *io)
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{
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struct stripe_head *sh, *next;
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list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
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list_del_init(&sh->log_list);
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r5c_finish_cache_stripe(sh);
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set_bit(STRIPE_HANDLE, &sh->state);
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raid5_release_stripe(sh);
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}
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@ -412,18 +501,19 @@ static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
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r5l_append_payload_page(log, sh->dev[i].page);
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}
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if (sh->qd_idx >= 0) {
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if (parity_pages == 2) {
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r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
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sh->sector, sh->dev[sh->pd_idx].log_checksum,
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sh->dev[sh->qd_idx].log_checksum, true);
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r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
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r5l_append_payload_page(log, sh->dev[sh->qd_idx].page);
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} else {
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} else if (parity_pages == 1) {
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r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
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sh->sector, sh->dev[sh->pd_idx].log_checksum,
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0, false);
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r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
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}
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} else /* Just writing data, not parity, in caching phase */
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BUG_ON(parity_pages != 0);
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list_add_tail(&sh->log_list, &io->stripe_list);
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atomic_inc(&io->pending_stripe);
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@ -455,6 +545,8 @@ int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
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return -EAGAIN;
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}
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WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
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for (i = 0; i < sh->disks; i++) {
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void *addr;
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@ -1112,6 +1204,49 @@ static void r5l_write_super(struct r5l_log *log, sector_t cp)
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set_bit(MD_CHANGE_DEVS, &mddev->flags);
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}
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/*
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* Try handle write operation in caching phase. This function should only
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* be called in write-back mode.
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*
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* If all outstanding writes can be handled in caching phase, returns 0
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* If writes requires write-out phase, call r5c_make_stripe_write_out()
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* and returns -EAGAIN
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*/
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int r5c_try_caching_write(struct r5conf *conf,
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struct stripe_head *sh,
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struct stripe_head_state *s,
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int disks)
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{
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struct r5l_log *log = conf->log;
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BUG_ON(!r5c_is_writeback(log));
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/* more write-back logic in next patches */
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r5c_make_stripe_write_out(sh);
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return -EAGAIN;
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}
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/*
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* clean up the stripe (clear R5_InJournal for dev[pd_idx] etc.) after the
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* stripe is committed to RAID disks.
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*/
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void r5c_finish_stripe_write_out(struct r5conf *conf,
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struct stripe_head *sh,
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struct stripe_head_state *s)
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{
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if (!conf->log ||
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!test_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags))
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return;
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WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
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clear_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);
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if (conf->log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
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return;
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BUG(); /* write-back logic in following patches */
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}
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static int r5l_load_log(struct r5l_log *log)
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{
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struct md_rdev *rdev = log->rdev;
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@ -1249,6 +1384,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
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INIT_LIST_HEAD(&log->no_space_stripes);
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spin_lock_init(&log->no_space_stripes_lock);
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log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
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if (r5l_load_log(log))
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goto error;
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@ -4107,6 +4107,9 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
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if (rdev && !test_bit(Faulty, &rdev->flags))
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do_recovery = 1;
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}
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if (test_bit(R5_InJournal, &dev->flags))
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s->injournal++;
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}
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if (test_bit(STRIPE_SYNCING, &sh->state)) {
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/* If there is a failed device being replaced,
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@ -4386,14 +4389,47 @@ static void handle_stripe(struct stripe_head *sh)
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|| s.expanding)
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handle_stripe_fill(sh, &s, disks);
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/* Now to consider new write requests and what else, if anything
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* should be read. We do not handle new writes when:
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/*
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* When the stripe finishes full journal write cycle (write to journal
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* and raid disk), this is the clean up procedure so it is ready for
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* next operation.
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*/
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r5c_finish_stripe_write_out(conf, sh, &s);
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/*
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* Now to consider new write requests, cache write back and what else,
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* if anything should be read. We do not handle new writes when:
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* 1/ A 'write' operation (copy+xor) is already in flight.
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* 2/ A 'check' operation is in flight, as it may clobber the parity
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* block.
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* 3/ A r5c cache log write is in flight.
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*/
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if (s.to_write && !sh->reconstruct_state && !sh->check_state)
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handle_stripe_dirtying(conf, sh, &s, disks);
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if (!sh->reconstruct_state && !sh->check_state && !sh->log_io) {
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if (!r5c_is_writeback(conf->log)) {
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if (s.to_write)
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handle_stripe_dirtying(conf, sh, &s, disks);
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} else { /* write back cache */
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int ret = 0;
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/* First, try handle writes in caching phase */
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if (s.to_write)
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ret = r5c_try_caching_write(conf, sh, &s,
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disks);
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/*
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* If caching phase failed: ret == -EAGAIN
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* OR
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* stripe under reclaim: !caching && injournal
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*
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* fall back to handle_stripe_dirtying()
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*/
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if (ret == -EAGAIN ||
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/* stripe under reclaim: !caching && injournal */
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(!test_bit(STRIPE_R5C_CACHING, &sh->state) &&
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s.injournal > 0))
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handle_stripe_dirtying(conf, sh, &s, disks);
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}
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}
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/* maybe we need to check and possibly fix the parity for this stripe
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* Any reads will already have been scheduled, so we just see if enough
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@ -5110,6 +5146,7 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
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* data on failed drives.
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*/
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if (rw == READ && mddev->degraded == 0 &&
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!r5c_is_writeback(conf->log) &&
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mddev->reshape_position == MaxSector) {
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bi = chunk_aligned_read(mddev, bi);
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if (!bi)
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@ -264,6 +264,7 @@ struct stripe_head_state {
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int syncing, expanding, expanded, replacing;
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int locked, uptodate, to_read, to_write, failed, written;
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int to_fill, compute, req_compute, non_overwrite;
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int injournal;
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int failed_num[2];
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int p_failed, q_failed;
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int dec_preread_active;
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@ -313,6 +314,11 @@ enum r5dev_flags {
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*/
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R5_Discard, /* Discard the stripe */
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R5_SkipCopy, /* Don't copy data from bio to stripe cache */
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R5_InJournal, /* data being written is in the journal device.
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* if R5_InJournal is set for parity pd_idx, all the
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* data and parity being written are in the journal
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* device
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*/
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};
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/*
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@ -345,7 +351,23 @@ enum {
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STRIPE_BITMAP_PENDING, /* Being added to bitmap, don't add
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* to batch yet.
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*/
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STRIPE_LOG_TRAPPED, /* trapped into log */
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STRIPE_LOG_TRAPPED, /* trapped into log (see raid5-cache.c)
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* this bit is used in two scenarios:
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*
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* 1. write-out phase
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* set in first entry of r5l_write_stripe
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* clear in second entry of r5l_write_stripe
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* used to bypass logic in handle_stripe
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*
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* 2. caching phase
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* set in r5c_try_caching_write()
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* clear when journal write is done
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* used to initiate r5c_cache_data()
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* also used to bypass logic in handle_stripe
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*/
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STRIPE_R5C_CACHING, /* the stripe is in caching phase
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* see more detail in the raid5-cache.c
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*/
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};
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#define STRIPE_EXPAND_SYNC_FLAGS \
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@ -710,4 +732,11 @@ extern void r5l_stripe_write_finished(struct stripe_head *sh);
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extern int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio);
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extern void r5l_quiesce(struct r5l_log *log, int state);
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extern bool r5l_log_disk_error(struct r5conf *conf);
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extern bool r5c_is_writeback(struct r5l_log *log);
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extern int
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r5c_try_caching_write(struct r5conf *conf, struct stripe_head *sh,
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struct stripe_head_state *s, int disks);
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extern void
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r5c_finish_stripe_write_out(struct r5conf *conf, struct stripe_head *sh,
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struct stripe_head_state *s);
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#endif
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