From 174364f6a8979655f71b04b6492657aec3762703 Mon Sep 17 00:00:00 2001 From: Damien Le Moal Date: Wed, 8 Jul 2020 09:20:22 +0900 Subject: [PATCH] dm zoned: Fix zone reclaim trigger 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 Signed-off-by: Damien Le Moal Reviewed-by: Hannes Reinecke Signed-off-by: Mike Snitzer --- drivers/md/dm-zoned-metadata.c | 9 ++++++++- drivers/md/dm-zoned-reclaim.c | 2 ++ drivers/md/dm-zoned-target.c | 10 +--------- 3 files changed, 11 insertions(+), 10 deletions(-) diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c index 5cf6f5f552e0..b298fefb022e 100644 --- a/drivers/md/dm-zoned-metadata.c +++ b/drivers/md/dm-zoned-metadata.c @@ -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; diff --git a/drivers/md/dm-zoned-reclaim.c b/drivers/md/dm-zoned-reclaim.c index 7e0cc2d732cf..9c0ecc9568a4 100644 --- a/drivers/md/dm-zoned-reclaim.c +++ b/drivers/md/dm-zoned-reclaim.c @@ -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; } diff --git a/drivers/md/dm-zoned-target.c b/drivers/md/dm-zoned-target.c index cf915009c306..42aa5139df7c 100644 --- a/drivers/md/dm-zoned-target.c +++ b/drivers/md/dm-zoned-target.c @@ -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); -- 2.39.5