> > Sorry, if I missed it, but I did not see any time overhead of moving a
> > task after these changes. Could you please help me understand the cost
> > of moving say a task with 1G anonymous memory to another group and
> > the cost of moving a task with 512MB anonymous and 512 page cache
> > mapped, etc. It would be nice to understand the overall cost.
> > 
> O.K.
> I'll test programs with big anonymous pages and measure the time and report.
> 
I measured the elapsed time of "echo <pid> > <some path>/tasks" on KVM guest
with 4CPU/4GB(Xeon/3GHz).

- used the attached simple program.
- made 2 directories(00, 01) under root, and enabled recharge_at_immigrate in both.
- measured the elapsed time by "time -p" for moving between:

  (1) root -> 00
  (2) 00 -> 01

  we don't need to call res_counter_uncharge against root, so (1) would be smaller
  than (2).

  (3) 00(setting mem.limit to half size of total) -> 01

  To compare the overhead of anon and swap.

Results:

       |  252M  |  512M  |   1G
  -----+--------+--------+--------
   (1) |  0.21  |  0.41  |  0.821
  -----+--------+--------+--------
   (2) |  0.43  |  0.85  |  1.71
  -----+--------+--------+--------
   (3) |  0.40  |  0.81  |  1.62
  -----+--------+--------+--------


hmm, it would be better to add some comments to memory.txt like:

  Note: It may take several seconds if you move charges in giga bytes order.


Regards,
Daisuke Nishimura.