I see. Thanks. On 9/29/20 12:03 AM, Mike Snitzer wrote:
On Sun, Sep 27 2020 at 8:04am -0400, Jeffle Xu <[email protected]> wrote:Hi Mike, would you mind further expalin why bio processed by dm_wq_work() always gets a previous ->submit_bio. Considering the following call graph: ->submit_bio, that is, dm_submit_bio DMF_BLOCK_IO_FOR_SUSPEND set, thus queue_io() then worker thread dm_wq_work() dm_process_bio // at this point. the input bio is the original bio submitted to dm device Please let me know if I missed something. Thanks. JeffleIn general you have a valid point, that blk_queue_split() won't have been done for the suspended device case, but blk_queue_split() cannot be used if not in ->submit_bio -- IIUC you cannot just do it from a worker thread and hope to have proper submission order (depth first) as provided by __submit_bio_noacct(). Because this IO will be submitted from worker you could have multiple threads allocating from the q->bio_split mempool at the same time. All said, I'm not quite sure how to address this report. But I'll keep at it and see what I can come up with. Thanks, MikeOriginal commit log: dm_process_bio() can be called by dm_wq_work(), and if the currently processing bio is the very beginning bio submitted to the dm device, that is it has not been handled by previous ->submit_bio, then we also need to impose the queue_limits when it's in thread (dm_wq_work()). Fixes: cf9c37865557 ("dm: fix comment in dm_process_bio()") Fixes: 568c73a355e0 ("dm: update dm_process_bio() to split bio if in ->make_request_fn()") Signed-off-by: Jeffle Xu <[email protected]> --- drivers/md/dm.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 6ed05ca65a0f..54471c75ddef 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1744,17 +1744,13 @@ static blk_qc_t dm_process_bio(struct mapped_device *md, }/*- * If in ->submit_bio we need to use blk_queue_split(), otherwise - * queue_limits for abnormal requests (e.g. discard, writesame, etc) - * won't be imposed. - * If called from dm_wq_work() for deferred bio processing, bio - * was already handled by following code with previous ->submit_bio. + * Call blk_queue_split() so that queue_limits for abnormal requests + * (e.g. discard, writesame, etc) are ensured to be imposed, while + * it's not needed for regular IO, since regular IO will be split by + * following __split_and_process_bio. */ - if (current->bio_list) { - if (is_abnormal_io(bio)) - blk_queue_split(&bio); - /* regular IO is split by __split_and_process_bio */ - } + if (is_abnormal_io(bio)) + blk_queue_split(&bio);if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)return __process_bio(md, map, bio, ti); -- 2.27.0
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