kernel/linux.git/drivers/md/raid5-cache.c, branch v4.11.5

md/raid5-cache: exclude reclaiming stripes in reclaim check

2017-02-13T17:20:05+00:00

stripes which are being reclaimed are still accounted into cached stripes. The reclaim takes time. r5c_do_reclaim isn't aware of the stripes and does unnecessary stripe reclaim. In practice, I saw one stripe is reclaimed one time. This will cause bad IO pattern. Fixing this by excluding the reclaing stripes in the check. Cc: Song Liu Signed-off-by: Shaohua Li

md/raid5-cache: stripe reclaim only counts valid stripes

2017-02-13T17:20:02+00:00

When log space is tight, we try to reclaim stripes from log head. There are stripes which can't be reclaimed right now if some conditions are met. We skip such stripes but accidentally count them, which might cause no stripes are claimed. Fixing this by only counting valid stripes. Cc: Song Liu Signed-off-by: Shaohua Li

md/r5cache: improve journal device efficiency

2017-02-13T17:17:52+00:00

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

md/r5cache: enable chunk_aligned_read with write back cache

2017-02-13T17:17:51+00:00

Chunk aligned read significantly reduces CPU usage of raid456. However, it is not safe to fully bypass the write back cache. This patch enables chunk aligned read with write back cache. For chunk aligned read, we track stripes in write back cache at a bigger granularity, "big_stripe". Each chunk may contain more than one stripe (for example, a 256kB chunk contains 64 4kB-page, so this chunk contain 64 stripes). For chunk_aligned_read, these stripes are grouped into one big_stripe, so we only need one lookup for the whole chunk. For each big_stripe, struct big_stripe_info tracks how many stripes of this big_stripe are in the write back cache. We count how many stripes of this big_stripe are in the write back cache. These counters are tracked in a radix tree (big_stripe_tree). r5c_tree_index() is used to calculate keys for the radix tree. chunk_aligned_read() calls r5c_big_stripe_cached() to look up big_stripe of each chunk in the tree. If this big_stripe is in the tree, chunk_aligned_read() aborts. This look up is protected by rcu_read_lock(). It is necessary to remember whether a stripe is counted in big_stripe_tree. Instead of adding new flag, we reuses existing flags: STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE. If either of these two flags are set, the stripe is counted in big_stripe_tree. This requires moving set_bit(STRIPE_R5C_PARTIAL_STRIPE) to r5c_try_caching_write(); and moving clear_bit of STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE to r5c_finish_stripe_write_out(). Signed-off-by: Song Liu Reviewed-by: NeilBrown Signed-off-by: Shaohua Li

md/r5cache: disable write back for degraded array

2017-01-24T19:26:06+00:00

write-back cache in degraded mode introduces corner cases to the array. Although we try to cover all these corner cases, it is safer to just disable write-back cache when the array is in degraded mode. In this patch, we disable writeback cache for degraded mode: 1. On device failure, if the array enters degraded mode, raid5_error() will submit async job r5c_disable_writeback_async to disable writeback; 2. In r5c_journal_mode_store(), it is invalid to enable writeback in degraded mode; 3. In r5c_try_caching_write(), stripes with s->failed>0 will be handled in write-through mode. Signed-off-by: Song Liu Signed-off-by: Shaohua Li

md/r5cache: flush data only stripes in r5l_recovery_log()

2017-01-24T19:20:15+00:00

For safer operation, all arrays start in write-through mode, which has been better tested and is more mature. And actually the write-through/write-mode isn't persistent after array restarted, so we always start array in write-through mode. However, if recovery found data-only stripes before the shutdown (from previous write-back mode), it is not safe to start the array in write-through mode, as write-through mode can not handle stripes with data in write-back cache. To solve this problem, we flush all data-only stripes in r5l_recovery_log(). When r5l_recovery_log() returns, the array starts with empty cache in write-through mode. This logic is implemented in r5c_recovery_flush_data_only_stripes(): 1. enable write back cache 2. flush all stripes 3. wake up conf->mddev->thread 4. wait for all stripes get flushed (reuse wait_for_quiescent) 5. disable write back cache The wait in 4 will be waked up in release_inactive_stripe_list() when conf->active_stripes reaches 0. It is safe to wake up mddev->thread here because all the resource required for the thread has been initialized. Signed-off-by: Song Liu Signed-off-by: Shaohua Li

md/r5cache: read data into orig_page for prexor of cached data

2017-01-24T19:20:14+00:00

With write back cache, we use orig_page to do prexor. This patch makes sure we read data into orig_page for it. Flag R5_OrigPageUPTDODATE is added to show whether orig_page has the latest data from raid disk. We introduce a helper function uptodate_for_rmw() to simplify the a couple conditions in handle_stripe_dirtying(). Signed-off-by: Song Liu Signed-off-by: Shaohua Li

md/raid5-cache: delete meaningless code

2017-01-24T19:20:13+00:00

sector_t is unsigned long, it's never < 0 Reported-by: Julia Lawall Signed-off-by: Shaohua Li

md/r5cache: fix spelling mistake on "recoverying"

2017-01-05T19:44:39+00:00

Trivial fix to spelling mistake "recoverying" to "recovering" in pr_dbg message. Signed-off-by: Colin Ian King Signed-off-by: Shaohua Li

md/r5cache: assign conf->log before r5l_load_log()

2017-01-05T19:44:38+00:00

r5l_load_log() calls functions that requires a proper conf->log, for example, r5c_is_writeback(). Therefore, we should set conf->log before calling r5l_load_log(). If r5l_load_log() fails, conf->log is set back to NULL. Signed-off-by: Song Liu Signed-off-by: Shaohua Li