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 <songliubraving@xxxxxx>
---
drivers/md/raid5-cache.c | 15 +++------------
drivers/md/raid5.c | 42 ++++++++++++++++++++++++++++++++----------
2 files changed, 35 insertions(+), 22 deletions(-)
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index b31ae41..c027f1b 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -387,17 +387,8 @@ 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 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 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.
+ * To flush all stripes in cache, we need (conf->max_degraded + 1)
+ * pages per stripe in cache.
*/
static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf)
{
@@ -406,7 +397,7 @@ 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) *
+ return BLOCK_SECTORS * (conf->max_degraded + 1) *
atomic_read(&log->stripe_in_journal_count);
}
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 193acd3..55a6156 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2953,13 +2953,35 @@ 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. to be added
+ * 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 dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags) &&
- !test_bit(R5_Insync, &dev->flags) && s->injournal;
+ /* case 1 above */
+ if (dev->towrite && !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
@@ -2982,7 +3004,7 @@ 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)
@@ -3733,7 +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) &&
@@ -3757,8 +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 */
@@ -3798,7 +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) &&
--
2.9.3
--
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