From 39b99586b321a9cbd4fe9abb5ea9346d2c4ca9c6 Mon Sep 17 00:00:00 2001 From: Song Liu Date: Tue, 24 Jan 2017 14:08:23 -0800 Subject: [PATCH] md/r5cache: improve journal device efficiency It is important to be able to flush all stripes in raid5-cache. Therefore, we need reserve some space on the journal device for these flushes. If flush operation includes pending writes to the stripe, we need to reserve (conf->raid_disk + 1) pages per stripe for the flush out. This reduces the efficiency of journal space. If we exclude these pending writes from flush operation, we only need (conf->max_degraded + 1) pages per stripe. With this patch, when log space is critical (R5C_LOG_CRITICAL=1), pending writes will be excluded from stripe flush out. Therefore, we can reduce reserved space for flush out and thus improve journal device efficiency. Signed-off-by: Song Liu Signed-off-by: Shaohua Li --- drivers/md/raid5-cache.c | 36 +++++++++++++++++++++++----------- drivers/md/raid5.c | 42 +++++++++++++++++++++++++++++++--------- 2 files changed, 58 insertions(+), 20 deletions(-) diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c index 76c0e5063f1b..caae85331a02 100644 --- a/drivers/md/raid5-cache.c +++ b/drivers/md/raid5-cache.c @@ -389,17 +389,30 @@ void r5c_check_cached_full_stripe(struct r5conf *conf) /* * Total log space (in sectors) needed to flush all data in cache * - * Currently, writing-out phase automatically includes all pending writes - * to the same sector. So the reclaim of each stripe takes up to - * (conf->raid_disks + 1) pages of log space. + * To avoid deadlock due to log space, it is necessary to reserve log + * space to flush critical stripes (stripes that occupying log space near + * last_checkpoint). This function helps check how much log space is + * required to flush all cached stripes. * - * To totally avoid deadlock due to log space, the code reserves - * (conf->raid_disks + 1) pages for each stripe in cache, which is not - * necessary in most cases. + * To reduce log space requirements, two mechanisms are used to give cache + * flush higher priorities: + * 1. In handle_stripe_dirtying() and schedule_reconstruction(), + * stripes ALREADY in journal can be flushed w/o pending writes; + * 2. In r5l_write_stripe() and r5c_cache_data(), stripes NOT in journal + * can be delayed (r5l_add_no_space_stripe). * - * To improve this, we will need writing-out phase to be able to NOT include - * pending writes, which will reduce the requirement to - * (conf->max_degraded + 1) pages per stripe in cache. + * In cache flush, the stripe goes through 1 and then 2. For a stripe that + * already passed 1, flushing it requires at most (conf->max_degraded + 1) + * pages of journal space. For stripes that has not passed 1, flushing it + * requires (conf->raid_disks + 1) pages of journal space. There are at + * most (conf->group_cnt + 1) stripe that passed 1. So total journal space + * required to flush all cached stripes (in pages) is: + * + * (stripe_in_journal_count - group_cnt - 1) * (max_degraded + 1) + + * (group_cnt + 1) * (raid_disks + 1) + * or + * (stripe_in_journal_count) * (max_degraded + 1) + + * (group_cnt + 1) * (raid_disks - max_degraded) */ static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf) { @@ -408,8 +421,9 @@ static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf) if (!r5c_is_writeback(log)) return 0; - return BLOCK_SECTORS * (conf->raid_disks + 1) * - atomic_read(&log->stripe_in_journal_count); + return BLOCK_SECTORS * + ((conf->max_degraded + 1) * atomic_read(&log->stripe_in_journal_count) + + (conf->raid_disks - conf->max_degraded) * (conf->group_cnt + 1)); } /* diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index b62f671a93ab..b0d1345c832c 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -2951,12 +2951,36 @@ sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous) * like to flush data in journal to RAID disks first, so complex rmw * is handled in the write patch (handle_stripe_dirtying). * + * 2. when journal space is critical (R5C_LOG_CRITICAL=1) + * + * It is important to be able to flush all stripes in raid5-cache. + * Therefore, we need reserve some space on the journal device for + * these flushes. If flush operation includes pending writes to the + * stripe, we need to reserve (conf->raid_disk + 1) pages per stripe + * for the flush out. If we exclude these pending writes from flush + * operation, we only need (conf->max_degraded + 1) pages per stripe. + * Therefore, excluding pending writes in these cases enables more + * efficient use of the journal device. + * + * Note: To make sure the stripe makes progress, we only delay + * towrite for stripes with data already in journal (injournal > 0). + * When LOG_CRITICAL, stripes with injournal == 0 will be sent to + * no_space_stripes list. + * */ -static inline bool delay_towrite(struct r5dev *dev, - struct stripe_head_state *s) +static inline bool delay_towrite(struct r5conf *conf, + struct r5dev *dev, + struct stripe_head_state *s) { - return !test_bit(R5_OVERWRITE, &dev->flags) && - !test_bit(R5_Insync, &dev->flags) && s->injournal; + /* case 1 above */ + if (!test_bit(R5_OVERWRITE, &dev->flags) && + !test_bit(R5_Insync, &dev->flags) && s->injournal) + return true; + /* case 2 above */ + if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) && + s->injournal > 0) + return true; + return false; } static void @@ -2979,7 +3003,7 @@ schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s, for (i = disks; i--; ) { struct r5dev *dev = &sh->dev[i]; - if (dev->towrite && !delay_towrite(dev, s)) { + if (dev->towrite && !delay_towrite(conf, dev, s)) { set_bit(R5_LOCKED, &dev->flags); set_bit(R5_Wantdrain, &dev->flags); if (!expand) @@ -3731,7 +3755,7 @@ static int handle_stripe_dirtying(struct r5conf *conf, } else for (i = disks; i--; ) { /* would I have to read this buffer for read_modify_write */ struct r5dev *dev = &sh->dev[i]; - if (((dev->towrite && !delay_towrite(dev, s)) || + if (((dev->towrite && !delay_towrite(conf, dev, s)) || i == sh->pd_idx || i == sh->qd_idx || test_bit(R5_InJournal, &dev->flags)) && !test_bit(R5_LOCKED, &dev->flags) && @@ -3755,8 +3779,8 @@ static int handle_stripe_dirtying(struct r5conf *conf, } } - pr_debug("for sector %llu, rmw=%d rcw=%d\n", - (unsigned long long)sh->sector, rmw, rcw); + pr_debug("for sector %llu state 0x%lx, rmw=%d rcw=%d\n", + (unsigned long long)sh->sector, sh->state, rmw, rcw); set_bit(STRIPE_HANDLE, &sh->state); if ((rmw < rcw || (rmw == rcw && conf->rmw_level == PARITY_PREFER_RMW)) && rmw > 0) { /* prefer read-modify-write, but need to get some data */ @@ -3796,7 +3820,7 @@ static int handle_stripe_dirtying(struct r5conf *conf, for (i = disks; i--; ) { struct r5dev *dev = &sh->dev[i]; - if (((dev->towrite && !delay_towrite(dev, s)) || + if (((dev->towrite && !delay_towrite(conf, dev, s)) || i == sh->pd_idx || i == sh->qd_idx || test_bit(R5_InJournal, &dev->flags)) && !test_bit(R5_LOCKED, &dev->flags) && -- GitLab