Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge whenobsolete

[KAMEZAWA Hiroyuki]

On Thu, 15 Jan 2009 09:47:50 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2009-01-15 12:24:16]:

> > But I don't like -EBUSY ;)
> > 
> > When rmdir() returns -EBUSY even if there are no (visible) children and tasks,
> > our customer will take kdump and send it to me "please explain this kernel bug"
> > 
> > I'm sure it will happen ;)
> >
> 
> OK, but memory.stat can show why the group is busy and with
> move_to_parent() such issues should not occur right? I'll relook at
> the code. Thanks for your input.
> 

There was a design choice at swap_cgroup.

At rmdir, there may be used swap entry in memcg. (mem->memsw.usage can be > 0)
  1. update all records in swap cgroup
  2. just ignore account from swap, we can treat then at swap-in.

I implemented "2" by refcnt.

To do "1", we have to scan all used swap_cgroup but I don't want to scan all
swap_cgroup entry at rmdir. It's heavy job.
(*) To reduce memory usage by swap_cgroup, swap_cgroup just have a pointer to memcg
(**) I implemented swap_cgroup as statically allocated array because I don't want
    any dynamic memory allocation at swap-out and want to avoid unnecessary memory
    usage.

Thanks,
-Kame

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