Vivek Goyal wrote: > On Fri, Sep 19, 2008 at 08:20:31PM +0900, Hirokazu Takahashi wrote: >>> To avoid creation of stacking another device (dm-ioband) on top of every >>> device we want to subject to rules, I was thinking of maintaining an >>> rb-tree per request queue. Requests will first go into this rb-tree upon >>> __make_request() and then will filter down to elevator associated with the >>> queue (if there is one). This will provide us the control of releasing >>> bio's to elevaor based on policies (proportional weight, max bandwidth >>> etc) and no need of stacking additional block device. >> I think it's a bit late to control I/O requests there, since process >> may be blocked in get_request_wait when the I/O load is high. >> Please imagine the situation that cgroups with low bandwidths are >> consuming most of "struct request"s while another cgroup with a high >> bandwidth is blocked and can't get enough "struct request"s. >> >> It means cgroups that issues lot of I/O request can win the game. >> > > Ok, this is a good point. Because number of struct requests are limited > and they seem to be allocated on first come first serve basis, so if a > cgroup is generating lot of IO, then it might win. > > But dm-ioband will face the same issue. Essentially it is also a request > queue and it will have limited number of request descriptors. Have you > modified the logic somewhere for allocation of request descriptors to the > waiting processes based on their weights? If yes, the logic probably can > be implemented here too. Maybe throttling dirty page ratio in memory could help to avoid this problem. I mean, if a cgroup is exceeding the i/o limits do ehm... something.. also at the balance_dirty_pages() level. -Andrea -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
