[Devel] Re: [PATCH 08/10] memcg: add cgroupfs interface to memcg dirty limits

[Andrea Righi]

On Wed, Oct 06, 2010 at 11:34:16AM -0700, Greg Thelen wrote:
> Andrea Righi <arighi at develer.com> writes:
> 
> > On Tue, Oct 05, 2010 at 12:33:15AM -0700, Greg Thelen wrote:
> >> KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> writes:
> >> 
> >> > On Sun,  3 Oct 2010 23:58:03 -0700
> >> > Greg Thelen <gthelen at google.com> wrote:
> >> >
> >> >> Add cgroupfs interface to memcg dirty page limits:
> >> >>   Direct write-out is controlled with:
> >> >>   - memory.dirty_ratio
> >> >>   - memory.dirty_bytes
> >> >> 
> >> >>   Background write-out is controlled with:
> >> >>   - memory.dirty_background_ratio
> >> >>   - memory.dirty_background_bytes
> >> >> 
> >> >> Signed-off-by: Andrea Righi <arighi at develer.com>
> >> >> Signed-off-by: Greg Thelen <gthelen at google.com>
> >> >
> >> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
> >> >
> >> > a question below.
> >> >
> >> >
> >> >> ---
> >> >>  mm/memcontrol.c |   89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >>  1 files changed, 89 insertions(+), 0 deletions(-)
> >> >> 
> >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> >> >> index 6ec2625..2d45a0a 100644
> >> >> --- a/mm/memcontrol.c
> >> >> +++ b/mm/memcontrol.c
> >> >> @@ -100,6 +100,13 @@ enum mem_cgroup_stat_index {
> >> >>  	MEM_CGROUP_STAT_NSTATS,
> >> >>  };
> >> >>  
> >> >> +enum {
> >> >> +	MEM_CGROUP_DIRTY_RATIO,
> >> >> +	MEM_CGROUP_DIRTY_BYTES,
> >> >> +	MEM_CGROUP_DIRTY_BACKGROUND_RATIO,
> >> >> +	MEM_CGROUP_DIRTY_BACKGROUND_BYTES,
> >> >> +};
> >> >> +
> >> >>  struct mem_cgroup_stat_cpu {
> >> >>  	s64 count[MEM_CGROUP_STAT_NSTATS];
> >> >>  };
> >> >> @@ -4292,6 +4299,64 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
> >> >>  	return 0;
> >> >>  }
> >> >>  
> >> >> +static u64 mem_cgroup_dirty_read(struct cgroup *cgrp, struct cftype *cft)
> >> >> +{
> >> >> +	struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
> >> >> +	bool root;
> >> >> +
> >> >> +	root = mem_cgroup_is_root(mem);
> >> >> +
> >> >> +	switch (cft->private) {
> >> >> +	case MEM_CGROUP_DIRTY_RATIO:
> >> >> +		return root ? vm_dirty_ratio : mem->dirty_param.dirty_ratio;
> >> >> +	case MEM_CGROUP_DIRTY_BYTES:
> >> >> +		return root ? vm_dirty_bytes : mem->dirty_param.dirty_bytes;
> >> >> +	case MEM_CGROUP_DIRTY_BACKGROUND_RATIO:
> >> >> +		return root ? dirty_background_ratio :
> >> >> +			mem->dirty_param.dirty_background_ratio;
> >> >> +	case MEM_CGROUP_DIRTY_BACKGROUND_BYTES:
> >> >> +		return root ? dirty_background_bytes :
> >> >> +			mem->dirty_param.dirty_background_bytes;
> >> >> +	default:
> >> >> +		BUG();
> >> >> +	}
> >> >> +}
> >> >> +
> >> >> +static int
> >> >> +mem_cgroup_dirty_write(struct cgroup *cgrp, struct cftype *cft, u64 val)
> >> >> +{
> >> >> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> >> >> +	int type = cft->private;
> >> >> +
> >> >> +	if (cgrp->parent == NULL)
> >> >> +		return -EINVAL;
> >> >> +	if ((type == MEM_CGROUP_DIRTY_RATIO ||
> >> >> +	     type == MEM_CGROUP_DIRTY_BACKGROUND_RATIO) && val > 100)
> >> >> +		return -EINVAL;
> >> >> +	switch (type) {
> >> >> +	case MEM_CGROUP_DIRTY_RATIO:
> >> >> +		memcg->dirty_param.dirty_ratio = val;
> >> >> +		memcg->dirty_param.dirty_bytes = 0;
> >> >> +		break;
> >> >> +	case MEM_CGROUP_DIRTY_BYTES:
> >> >> +		memcg->dirty_param.dirty_bytes = val;
> >> >> +		memcg->dirty_param.dirty_ratio  = 0;
> >> >> +		break;
> >> >> +	case MEM_CGROUP_DIRTY_BACKGROUND_RATIO:
> >> >> +		memcg->dirty_param.dirty_background_ratio = val;
> >> >> +		memcg->dirty_param.dirty_background_bytes = 0;
> >> >> +		break;
> >> >> +	case MEM_CGROUP_DIRTY_BACKGROUND_BYTES:
> >> >> +		memcg->dirty_param.dirty_background_bytes = val;
> >> >> +		memcg->dirty_param.dirty_background_ratio = 0;
> >> >> +		break;
> >> >
> >> >
> >> > Curious....is this same behavior as vm_dirty_ratio ?
> >> 
> >> I think this is same behavior as vm_dirty_ratio.  When vm_dirty_ratio is
> >> changed then dirty_ratio_handler() will set vm_dirty_bytes=0.  When
> >> vm_dirty_bytes is written dirty_bytes_handler() will set
> >> vm_dirty_ratio=0.  So I think that the per-memcg dirty memory parameters
> >> mimic the behavior of vm_dirty_ratio, vm_dirty_bytes and the other
> >> global dirty parameters.
> >> 
> >> Am I missing your question?
> >
> > mmh... looking at the code it seems the same behaviour, but in
> > Documentation/sysctl/vm.txt we say a different thing (i.e., for
> > dirty_bytes):
> >
> > "If dirty_bytes is written, dirty_ratio becomes a function of its value
> > (dirty_bytes / the amount of dirtyable system memory)."
> >
> > However, in dirty_bytes_handler()/dirty_ratio_handler() we actually set
> > the counterpart value as 0.
> >
> > I think we should clarify the documentation.
> >
> > Signed-off-by: Andrea Righi <arighi at develer.com>
> 
> Reviewed-by: Greg Thelen <gthelen at google.com>
> 
> This documentation change is general cleanup that is independent of the
> memcg patch series shown on the subject.

Thanks Greg. I'll resend it as an independent patch.

-Andrea
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