Hi Mike,

On 17/11/21 05:02, Mike Snitzer wrote:

On Sun, Nov 19, 2017 at 9:00 PM, Joseph Qi [off-list ref] wrote:

quoted

From: Joseph Qi <redacted>

dm device set QUEUE_FLAG_NONROT in resume, which is after register
queue. That is to mean, the previous initialization in
blk_throtl_register_queue is wrong in this case.
Fix it by checking and then updating the info during root tg
initialization as we don't have a better choice.

Given DM motivated this change, curious why you didn't send this to dm-devel?

Since this is io.low specifically, I don't want the change in device
mapper layer. But I do agree with you that I have to cc dm-devel as
well. Sorry for missing that.

In any case, not sure why you need to reference "resume".  Very few
people will appreciate that detail.

Better to just say: DM device sets QUEUE_FLAG_NONROT after the queue
is registered.

Thanks for your advice. I will update and resend it.

Thanks,
Joseph

quoted

Signed-off-by: Joseph Qi <redacted>
---
 block/blk-throttle.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index bf52035..6d6b220 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c

@@ -541,6 +541,23 @@ static void throtl_pd_init(struct blkg_policy_data *pd)
        if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
                sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
        tg->td = td;
+
+       /*
+        * dm device set QUEUE_FLAG_NONROT in resume, which is after resister
+        * queue, so the previous initialization is wrong in this case. Check
+        * and update it here.
+        */

typo: s/resister/register/
But again, best to say:
DM device sets QUEUE_FLAG_NONROT after the queue is registered, ...

Also, an alternative to your patch would be to have DM's
dm_table_set_restrictions() call a blk-throttle function to setup
blk-throttle after it is done setting queue flags?
Saves all other drivers from having to run this 2 stage initialization
code.. just a thought.

Mike