Re: [PATCH RFC v2 5/6] blk-throttle: support to destroy throtl_data when blk-throttle is disabled
From: Yu Kuai
Date: Tue Apr 16 2024 - 21:40:05 EST
Hi,
在 2024/04/17 9:22, Tejun Heo 写道:
Hello,
On Wed, Apr 17, 2024 at 09:13:34AM +0800, Yu Kuai wrote:
Probably a better interface is for unloading to force blk-throtl to be
deactivated rather than asking the user to nuke all configs.
I was thinking that rmmod in this case should return busy, for example,
if bfq is currently used for some disk, rmmod bfq will return busy.
Is there any example that unloading will deactivate resources that users
are still using?
Hmm... yeah, I'm not sure. Pinning the module while in use is definitely
more conventional, so let's stick with that. It's usually achieved by
inc'ing the module's ref on each usage, so here, the module refs would be
counting the number of active rules, I guess.
Yes, aggred.
I'm not sure about modularization tho mostly because we've historically had
a lot of lifetime issues around block and blkcg data structures and the
supposed gain here is rather minimal. We only have a handful of these
policies and they aren't that big.
If hot path overhead when not being used is concern, lazy init solves most
of it, no?
For performance, yes. Another point is that we can reduce kernel size
this way, without losing support for blk-cgroup policies.
Yes, it's just blk-throttle is the most pain in the ass becasue it
exposed lots of implementations to block layer. Other rq_qos based
policy should be much easier.
I guess I'll do lazy init first, and then modularization for rq_qos,
and leave blk-throtl there for now. Perhaps add a new throtl model in
iocost can replace blk-throtl in the future.
BTW, currently during test of iocost, I found that iocost can already
achieve that, for example, by following configure:
echo "$dev enable=1 min=100 max=100" > qos
echo "$dev wbps=4096 wseqiops=1 wrandiops=1" > model
In the test, I found that wbps and iops is actually limited to the
set value.
Thanks,
Kuai
Thanks.