[dm-devel] [PATCH] block: transfer source bio's cgroup tags to clone via bio_associate_blkcg() (was: Re: blkio cgroups controller doesn't work with LVM?)

[Nikolay Borisov]

On Wednesday, March 2, 2016, Vivek Goyal <vgoyal at redhat.com> wrote:

> On Wed, Mar 02, 2016 at 08:03:10PM +0200, Nikolay Borisov wrote:
> > Thanks for the patch I will likely have time to test this sometime next
> week.
> > But just to be sure - the expected behavior would be that processes
> > writing to dm-based devices would experience the fair-shair
> > scheduling of CFQ (provided that the physical devices that back those
> > DM devices use CFQ), correct?
>
> Nikolay,
>
> I am not sure how well it will work with CFQ of underlying device. It will
> get cgroup information right for buffered writes. But cgroup information


 Right, what's your definition of  buffered writes? My mental model is that
when a process submits a write request to a dm device , the bio is going to
be put on a devi e workqueue which would then  be serviced by a background
worker thread and later the submitter notified. Do you refer to this whole
gamut of operations as buffered writes?

for reads and direct writes will come from submitter's context and if dm
> layer gets in between, then many a times submitter might be a worker
> thread and IO will be attributed to that worker's cgroup (root cgroup).


Be that as it may, proivded that the worker thread is in the  'correct'
cgroup,  then the appropriate babdwidth policies should apply, no?

>
> Give it a try anyway.


Most certainly I will :)


>
> Thanks
> Vivek
>
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