linux-kernel - Re: [PATCHSET 1/3 v2 block/for-4.1/core] writeback: cgroup writeback support

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Date:	Wed, 25 Mar 2015 11:40:22 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, jack@...e.cz,
	hch@...radead.org, hannes@...xchg.org,
	linux-fsdevel@...r.kernel.org, lizefan@...wei.com,
	cgroups@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.cz,
	clm@...com, fengguang.wu@...el.com, david@...morbit.com,
	gthelen@...gle.com
Subject: Re: [PATCHSET 1/3 v2 block/for-4.1/core] writeback: cgroup writeback
 support

On Mon, Mar 23, 2015 at 12:54:11AM -0400, Tejun Heo wrote:
> 
> 
> How to test
> -----------
> 
> * Boot with kernel option "cgroup__DEVEL__legacy_files_on_dfl".
> 
> * umount /sys/fs/cgroup/memory
>   umount /sys/fs/cgroup/blkio
>   mkdir /sys/fs/cgroup/unified
>   mount -t cgroup -o __DEVEL__sane_behavior cgroup /sys/fs/cgroup/unified
>   echo +blkio > /sys/fs/cgroup/unified/cgroup.subtree_control
> 
> * Build the cgroup hierarchy (don't forget to enable blkio using
>   subtree_control) and put processes in cgroups and run tests on ext2
>   filesystems and blkio.throttle.* knobs.
> 

[..]
> This patchset is on top of
> 
>   block/for-4.1/core bfd343aa1718 ("blk-mq: don't wait in blk_mq_queue_enter() if __GFP_WAIT isn't set")
> + [1] [PATCH] writeback: fix possible underflow in write bandwidth calculation
> 
> and available in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cgroup-writeback-20150322
> 

Hi Tejun,

Great Work. I tried to do some basic testing and it seems to work.

I used "review-cgroup-writeback-switch-20150322" branch for my testing.

I have 32G of RAM on my system and I setup a write bandwidth of 1MB/s
on the disk and allowed a dd to run. That dd quickly consumed 5G of
page cache before it reached to a steady state. Sounds like too much
of cache consumption which will be drained at a speed of 1MB/s. Not
sure if this is expected or bdi back-pressure is not being applied soon
enough.

Thanks
Vivek
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