Nauman Rafique wrote: > On Fri, May 8, 2009 at 6:57 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: >> On Fri, May 08, 2009 at 05:45:32PM +0800, Gui Jianfeng wrote: >>> Hi Vivek, >>> >>> This patch adds io group reference handling when allocating >>> and removing a request. >>> >> Hi Gui, >> >> Thanks for the patch. We were thinking that requests can take a reference >> on io queues and io queues can take a reference on io groups. That should >> make sure that io groups don't go away as long as active requests are >> present. >> >> But there seems to be a small window while allocating the new request >> where request gets allocated from a group first and then later it is >> mapped to that group and queue is created. IOW, in get_request_wait(), >> we allocate a request from a particular group and set rq->rl, then >> drop the queue lock and later call elv_set_request() which again maps >> the request to the group saves rq->iog and creates new queue. This window >> is troublesome because request can be mapped to a particular group at the >> time of allocation and during set_request() it can go to a different >> group as queue lock was dropped and group might have disappeared. >> >> In this case probably it might make sense that request also takes a >> reference on groups. At the same time it looks too much that request takes >> a reference on queue as well as group object. Ideas are welcome on how >> to handle it... > > IMHO a request being allocated on the wrong cgroup should not be a big > problem as such. All it means is that the request descriptor was > accounted to the wrong cgroup in this particular corner case. Please > correct me if I am wrong. > > We can also get rid of rq->iog pointer too. What that means is that > request is associated with ioq (rq->ioq), and we can use > ioq_to_io_group() function to get the io_group. So the request would > only be indirectly associated with an io_group i.e. the request is > associated with an io_queue and the io_group for the request is the > io_group associated with io_queue. Do you see any problems with that > approach? That sounds reasonable to get rid of rq->iog, and rq->rl is also dead. Hope to see the patch soon. ;) -- Regards Gui Jianfeng -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
