cgroup writeback support

cgroup writeback support

[张本龙]

Hello Tejun & cgroup,

I encountered several questions playing with cgroup that I really hope
to get your answers.

I referred to this LWN article for writeback support
https://lwn.net/Articles/628631/ and did following steps:
- clone git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git
and checkout branch review-cgroup-writeback-20150106
- compile and boot with option cgroup__DEVEL__legacy_files_on_dfl
- umount all subsys then do mount -t cgroup -o __DEVEL__sane_behavior
cgroup /sys/fs/cgroup/
- found blkio memory already in cgroup.subtree_control as default
- created new group /sys/fs/cgroup/bash, and play with IO throttling
both with iops and wbps, both on my sda ext4 and sdb ext2
Then I found it's not working... I realized the article states only
ext2 was adapted but it's not working either : )

Then I turned to this page
https://kernelnewbies.org/Linux_4.2#head-8f54d7519fca6b2504f5f26290f46081d6cb6927
saying Linux-4.2 has writeback support. I did similar steps as above
except cloning from linux-stable.git, and it's not working either. I
noticed this code is largely different from the
review-cgroup-writeback-20150106 branch based on 3.19.0 (e.g.,
dirty_context).

However Linux-4.3.3 and Linux-4.10.0 really works, except that control
files have changed in 4.3.3 and we can directly use cgroup2 in 4.10.0.

Is it because I did something wrong or missed anything? As I find many
branches exist in kernel/git/tj/cgroup.tj, it would be great if you
could help explain the roles of the different branches and how the
repo works in general. Especially, I want to know the first repo
branch/linux release that has writeback support so it's easier to
learn how it's built up step by step from the commit log.

Thank you very much!
Benlong

Re: cgroup writeback support

[Tejun Heo]

Hello,

On Wed, Apr 19, 2017 at 05:58:56PM +0800, 张本龙 wrote:
> Is it because I did something wrong or missed anything? As I find many
> branches exist in kernel/git/tj/cgroup.tj, it would be great if you
> could help explain the roles of the different branches and how the

Heh, those are from a long time ago.  These are all work-in-progress
branches and trying to chase down which branch was for what won't be
easy.  They're mostly ad-hoc.

> repo works in general. Especially, I want to know the first repo
> branch/linux release that has writeback support so it's easier to
> learn how it's built up step by step from the commit log.

If it's for tracking down the commits to help understanding the code,
I'd recommend tracking down the history with git whatchanged on the
main files (fs/fs-writeback.c and mm/backing-dev.c and
mm/page-writeback.c) and then browse the commits from there.

Thanks.

-- 
tejun