md/r5cache: improve journal device efficiency (39b99586) · Commits · 戴 / test

drivers/md/raid5-cache.c

+25 −11

Original line number	Diff line number	Diff line
		@@ -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));
		}

		/*

drivers/md/raid5.c

+33 −9

Original line number	Diff line number	Diff line
		@@ -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,
		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) &&

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