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blk-mq: prealloc tags when increase tagset nr_hw_queues
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Just like blk_mq_alloc_tag_set(), it's better to prepare all tags before
using to map to queue ctxs in blk_mq_map_swqueue(), which now have to
consider empty set->tags[].

The good point is that we can fallback easily if increasing nr_hw_queues
fail, instead of just mapping to hctx[0] when fail in blk_mq_map_swqueue().

And the fallback path already has tags free & clean handling, so all
is good.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230821095602.70742-3-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Chengming Zhou authored and Jens Axboe committed Aug 22, 2023
1 parent 2bc4d7a commit 7222657
Showing 1 changed file with 10 additions and 0 deletions.
10 changes: 10 additions & 0 deletions block/blk-mq.c
Original file line number Diff line number Diff line change
Expand Up @@ -4397,6 +4397,16 @@ static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
sizeof(*set->tags));
kfree(set->tags);
set->tags = new_tags;

for (i = set->nr_hw_queues; i < new_nr_hw_queues; i++) {
if (!__blk_mq_alloc_map_and_rqs(set, i)) {
while (--i >= set->nr_hw_queues)
__blk_mq_free_map_and_rqs(set, i);
return -ENOMEM;
}
cond_resched();
}

done:
set->nr_hw_queues = new_nr_hw_queues;
return 0;
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