Re: [PATCH 2/2] memcg: dirty pages instrumentation

[Andrea Righi <arighi@develer.com>]

On Tue, Feb 23, 2010 at 10:40:40AM +0100, Andrea Righi wrote:
> > If vm_highmem_is_dirtyable=0, In that case, we can still return with
> > "memcg_memory" which can be more than "memory".  IOW, highmem is not
> > dirtyable system wide but still we can potetially return back saying
> > for this cgroup we can dirty more pages which can potenailly be acutally
> > be more that system wide allowed?
> > 
> > Because you have modified dirtyable_memory() and made it per cgroup, I
> > think it automatically takes care of the cases of per cgroup dirty ratio,
> > I mentioned in my previous mail. So we will use system wide dirty ratio
> > to calculate the allowed dirty pages in this cgroup (dirty_ratio *
> > available_memory()) and if this cgroup wrote too many pages start
> > writeout? 
> 
> OK, if I've understood well, you're proposing to use per-cgroup
> dirty_ratio interface and do something like:
> 
> unsigned long determine_dirtyable_memory(void)
> {
> 	unsigned long memcg_memory, memory;
> 
> 	memory = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
> 	if (!vm_highmem_is_dirtyable)
> 		memory -= highmem_dirtyable_memory(memory);
> 
> 	memcg_memory = mem_cgroup_page_state(MEMCG_NR_FREE_PAGES);
> 	if (!memcg_memory)
> 		return memory + 1;      /* Ensure that we never return 0 */
> 	memcg_memory += mem_cgroup_page_state(MEMCG_NR_RECLAIMABLE_PAGES);
> 	if (!vm_highmem_is_dirtyable)
> 		 memcg_memory -= highmem_dirtyable_memory(memory) *
> 					mem_cgroup_dirty_ratio() / 100;

ok, this is wrong:

> 	if (memcg_memory < memory)
> 		return memcg_memory;
> }

	return min(memcg_memory, memory);

-Andrea