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SubjectRe: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v6)
On Thu, Mar 11, 2010 at 01:07:53PM -0500, Vivek Goyal wrote:
> On Wed, Mar 10, 2010 at 12:00:31AM +0100, Andrea Righi wrote:
> > Control the maximum amount of dirty pages a cgroup can have at any given time.
> >
> > Per cgroup dirty limit is like fixing the max amount of dirty (hard to reclaim)
> > page cache used by any cgroup. So, in case of multiple cgroup writers, they
> > will not be able to consume more than their designated share of dirty pages and
> > will be forced to perform write-out if they cross that limit.
> >
> > The overall design is the following:
> >
> > - account dirty pages per cgroup
> > - limit the number of dirty pages via memory.dirty_ratio / memory.dirty_bytes
> > and memory.dirty_background_ratio / memory.dirty_background_bytes in
> > cgroupfs
> > - start to write-out (background or actively) when the cgroup limits are
> > exceeded
> >
> > This feature is supposed to be strictly connected to any underlying IO
> > controller implementation, so we can stop increasing dirty pages in VM layer
> > and enforce a write-out before any cgroup will consume the global amount of
> > dirty pages defined by the /proc/sys/vm/dirty_ratio|dirty_bytes and
> > /proc/sys/vm/dirty_background_ratio|dirty_background_bytes limits.
> >
>
> Hi Andrea,
>
> I am doing a simple dd test of writting a 4G file. This machine has got
> 64G of memory and I have created one cgroup with 100M as limit_in_bytes.
>
> I run following dd program both in root cgroup as well as test1/
> cgroup(100M limit) one after the other.
>
> In root cgroup
> ==============
> dd if=/dev/zero of=/root/zerofile bs=4K count=1000000
> 1000000+0 records in
> 1000000+0 records out
> 4096000000 bytes (4.1 GB) copied, 59.5571 s, 68.8 MB/s
>
> In test1/ cgroup
> ===============
> dd if=/dev/zero of=/root/zerofile bs=4K count=1000000
> 1000000+0 records in
> 1000000+0 records out
> 4096000000 bytes (4.1 GB) copied, 20.6683 s, 198 MB/s
>
> It is strange that we are throttling process in root group much more than
> process in test1/ cgroup?

mmmh.. strange, on my side I get something as expected:

<root cgroup>
$ dd if=/dev/zero of=test bs=1M count=500
500+0 records in
500+0 records out
524288000 bytes (524 MB) copied, 6.28377 s, 83.4 MB/s

<child cgroup with 100M memory.limit_in_bytes>
$ dd if=/dev/zero of=test bs=1M count=500
500+0 records in
500+0 records out
524288000 bytes (524 MB) copied, 11.8884 s, 44.1 MB/s

Did you change the global /proc/sys/vm/dirty_* or memcg dirty
parameters?

-Andrea


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