Only triggering reclaim based on the percentage of unmapped cache
zones can fail to detect cases where reclaim is needed, e.g. if the
target has only 2 or 3 cache zones and only one unmapped cache zone,
the percentage of free cache zones is higher than
DMZ_RECLAIM_LOW_UNMAP_ZONES (30%) and reclaim does not trigger.
This problem, combined with the fact that dmz_schedule_reclaim() is
called from dmz_handle_bio() without the map lock held, leads to a
race between zone allocation and dmz_should_reclaim() result.
Depending on the workload applied, this race can lead to the write
path waiting forever for a free zone without reclaim being triggered.
Fix this by moving dmz_schedule_reclaim() inside dmz_alloc_zone()
under the map lock. This results in checking the need for zone reclaim
whenever a new data or buffer zone needs to be allocated.
Also fix dmz_reclaim_percentage() to always return 0 if the number of
unmapped cache (or random) zones is less than or equal to 1.
Suggested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
{
struct list_head *list;
struct dm_zone *zone;
- int i = 0;
+ int i;
+
+ /* Schedule reclaim to ensure free zones are available */
+ if (!(flags & DMZ_ALLOC_RECLAIM)) {
+ for (i = 0; i < zmd->nr_devs; i++)
+ dmz_schedule_reclaim(zmd->dev[i].reclaim);
+ }
+ i = 0;
again:
if (flags & DMZ_ALLOC_CACHE)
list = &zmd->unmap_cache_list;
nr_zones = dmz_nr_rnd_zones(zmd, zrc->dev_idx);
nr_unmap = dmz_nr_unmap_rnd_zones(zmd, zrc->dev_idx);
}
+ if (nr_unmap <= 1)
+ return 0;
return nr_unmap * 100 / nr_zones;
}
dm_per_bio_data(bio, sizeof(struct dmz_bioctx));
struct dmz_metadata *zmd = dmz->metadata;
struct dm_zone *zone;
- int i, ret;
-
- /*
- * Write may trigger a zone allocation. So make sure the
- * allocation can succeed.
- */
- if (bio_op(bio) == REQ_OP_WRITE)
- for (i = 0; i < dmz->nr_ddevs; i++)
- dmz_schedule_reclaim(dmz->dev[i].reclaim);
+ int ret;
dmz_lock_metadata(zmd);