dm zoned: Fix zone reclaim trigger (174364f6) · Commits · 戴 / test

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>

drivers/md/dm-zoned-metadata.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -2217,8 +2217,15 @@ struct dm_zone dmz_alloc_zone(struct dmz_metadata zmd, unsigned int dev_idx,
		{
		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;

drivers/md/dm-zoned-reclaim.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -456,6 +456,8 @@ static unsigned int dmz_reclaim_percentage(struct dmz_reclaim *zrc)
		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;
		}

drivers/md/dm-zoned-target.c

+1 −9

Original line number	Diff line number	Diff line
		@@ -400,15 +400,7 @@ static void dmz_handle_bio(struct dmz_target dmz, struct dm_chunk_work cw,
		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);

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