[Devel] Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v6)

[Vivek Goyal]

On Fri, Mar 12, 2010 at 12:59:22AM +0100, Andrea Righi wrote:
> 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?

No I did not change any memecg dirty parameters.

Vivek
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