Re: [PATCH 3/5] page_cgroup: make page tracking available for blkio

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 23 Feb 2011 09:59:11 +0100
Andrea Righi <arighi@develer.com> wrote:

> > 
> > I wonder I can make pc->mem_cgroup to be pc->memid(16bit), then, 
> > ==
> > static inline struct mem_cgroup *get_memcg_from_pc(struct page_cgroup *pc)
> > {
> >     struct cgroup_subsys_state *css = css_lookup(&mem_cgroup_subsys, pc->memid);
> >     return container_of(css, struct mem_cgroup, css);
> > }
> > ==
> > Overhead will be seen at updating file statistics and LRU management.
> > 
> > But, hmm, can't you do that tracking without page_cgroup ?
> > Because the number of dirty/writeback pages are far smaller than total pages,
> > chasing I/O with dynamic structure is not very bad..
> > 
> > prepareing [pfn -> blkio] record table and move that information to struct bio
> > in dynamic way is very difficult ?
> 
> This would be ok for dirty pages, but consider that we're also tracking
> anonymous pages. So, if we want to control the swap IO we actually need
> to save this information for a lot of pages and at the end I think we'll
> basically duplicate the page_cgroup code.
> 

swap io is always started with bio and the task/mm_struct.
So, if we can record information in bio, no page tracking is required.
You can record information to bio just by reading mm->owner.

Thanks,
-Kame

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