diff options
Diffstat (limited to 'drivers/md/raid5-cache.c')
| -rw-r--r-- | drivers/md/raid5-cache.c | 36 |
1 files changed, 25 insertions, 11 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)); } /* |