在 2024/6/25 18:34, Michal Koutný 写道:
Hello.
On Mon, Jun 24, 2024 at 09:09:40PM GMT, Li Lingfeng <lilingfeng@xxxxxxxxxxxxxxx> wrote:
From: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
When a process migrates to another cgroup and the original cgroup is deleted,
the restrictions of throttled bios cannot be removed. If the restrictions
are set too low, it will take a long time to complete these bios.
When pd_offline_fn is called because of disk going away, it makes sense
to cancel the bios. However, when pd_offline_fn is called due to cgroup
removal (with possibly surviving originating process), wouldn't bio
cancelling lead to loss of data?
Aha, it wouldn't -- the purpose of the function is to "flush" throttled
bios (in the original patch they'd immediately fail, here they the IO
operation may succeed).
Is that correct? (Wouldn't there be a more descriptive name than
tg_cancel_bios then?)
Thanks for your advice. It's indeed more appropriate to use "flush"
instead of "cancel" here, I will change it soon.
And if a user is allowed to remove cgroup and use this to bypass the
throttling, they also must have permissions to migrate away from the
cgroup (and consistent config would thus allow them to change the limit
too), therefore this doesn't allow bypassing the throttling limit. If
you agree, could you please add the explanation to commit message too?
I didn't quite get what you mean. Do you mean this patch will cause a
change in mechanics, and it is necessary to add an explanation?
(After deleting the original cgroup,
Before: the limit of the throttled bios can't be changed and the bios
will complete under this limit;
Now: the limit will be canceled and the throttled bios will be flushed
immediately.)
Thanks,
Michal
