[Devel] Re: [PATCH 0/5] blk-throttle: writeback and swap IO control

[Balbir Singh]

* Andrea Righi <arighi at develer.com> [2011-02-22 18:12:51]:

> Currently the blkio.throttle controller only support synchronous IO requests.
> This means that we always look at the current task to identify the "owner" of
> each IO request.
> 
> However dirty pages in the page cache can be wrote to disk asynchronously by
> the per-bdi flusher kernel threads or by any other thread in the system,
> according to the writeback policy.
> 
> For this reason the real writes to the underlying block devices may
> occur in a different IO context respect to the task that originally
> generated the dirty pages involved in the IO operation. This makes the
> tracking and throttling of writeback IO more complicate respect to the
> synchronous IO from the blkio controller's perspective.
> 
> The same concept is also valid for anonymous pages involed in IO operations
> (swap).
> 
> This patch allow to track the cgroup that originally dirtied each page in page
> cache and each anonymous page and pass these informations to the blk-throttle
> controller. These informations can be used to provide a better service level
> differentiation of buffered writes swap IO between different cgroups.
> 
> Testcase
> ========
> - create a cgroup with 1MiB/s write limit:
>   # mount -t cgroup -o blkio none /mnt/cgroup
>   # mkdir /mnt/cgroup/foo
>   # echo 8:0 $((1024 * 1024)) > /mnt/cgroup/foo/blkio.throttle.write_bps_device
> 
> - move a task into the cgroup and run a dd to generate some writeback IO
> 
> Results:
>   - 2.6.38-rc6 vanilla:
>   $ cat /proc/$$/cgroup
>   1:blkio:/foo
>   $ dd if=/dev/zero of=zero bs=1M count=1024 &
>   $ dstat -df
>   --dsk/sda--
>    read  writ
>      0    19M
>      0    19M
>      0     0
>      0     0
>      0    19M
>   ...
> 
>   - 2.6.38-rc6 + blk-throttle writeback IO control:
>   $ cat /proc/$$/cgroup
>   1:blkio:/foo
>   $ dd if=/dev/zero of=zero bs=1M count=1024 &
>   $ dstat -df
>   --dsk/sda--
>    read  writ
>      0  1024
>      0  1024
>      0  1024
>      0  1024
>      0  1024
>   ...
> 

Thanks for looking into this, further review follows.

-- 
	Three Cheers,
	Balbir
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