On Mon, 18 Apr 2011 08:38:24 +0200 Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote: > On 2011-04-18 00:19, NeilBrown wrote: > > On Mon, 11 Apr 2011 14:11:58 +0200 Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote: > > > >>> Yes. But I need to know when to release the requests that I have stored. > >>> I need to know when ->write_pages or ->read_pages or whatever has finished > >>> submitting a pile of pages so that I can start processing the request that I > >>> have put aside. So I need a callback from blk_finish_plug. > >> > >> OK fair enough, I'll add your callback patch. > >> > > > > But you didn't did you? You added a completely different patch which is > > completely pointless. > > If you don't like my patch I would really prefer you said so rather than > > silently replace it with something completely different (and broken). > > First of all, you were CC'ed on all that discussion, yet didn't speak up > until now. This was last week. Secondly, please change your tone. Yes, I was CC'ed on a discussion. In that discussion it was never mentioned that you had completely changed the patch I sent you, and it never contained the new patch in-line for review. Nothing that was discussed was particularly relevant to md's needs so there was nothing to speak up about. Yes- there were 'git pull' requests and I could have done a pull myself to review the code but there seemed to be no urgency because you had already agreed to apply my patch. When I did finally pull the patches (after all the other issues had settle down and I had time to finish of the RAID side) I found ... what I found. I apologise for my tone, but I was very frustrated. > > > I'll try to explain again. > > > > md does not use __make_request. At all. > > md does not use 'struct request'. At all. > > > > The 'list' in 'struct blk_plug' is a list of 'struct request'. > > I'm well aware of how these facts, but thanks for bringing it up. > > > Therefore md cannot put anything useful on the list in 'struct blk_plug'. > > > > So when blk_flush_plug_list calls queue_unplugged() on a queue that belonged > > to a request found on the blk_plug list, that queue cannot possibly ever be > > for an 'md' device (because no 'struct request' ever belongs to an md device, > > because md doesn't not use 'struct request'). > > > > So your patch (commit f75664570d8b) doesn't help MD at all. > > > > For md, I need to attach something to blk_plug which somehow identifies an md > > device, so that blk_finish_plug can get to that device and let it unplug. > > The most sensible thing to have is a completely generic callback. That way > > different block devices (which choose not to use __make_request) can attach > > different sorts of things to blk_plug. > > > > So can we please have my original patch applied? (Revised version using > > list_splice_init included below). > > > > Or if not, a clear explanation of why not? > > So correct me if I'm wrong here, but the _only_ real difference between > this patch and the current code in the tree, is the checking of the > callback list indicating a need to flush the callbacks. And that's > definitely an oversight. It should be functionally equivelant if md > would just flag this need to get a callback, eg instead of queueing a > callback on the list, just set plug->need_unplug from md instead of > queuing a callback and have blk_needs_flush_plug() do: > > return plug && (!list_empty(&plug->list) || plug->need_unplug); > > instead. Something like the below, completely untested. > No, that is not the only real difference. The real difference is that in the current code, md has no way to register anything with a blk_plug because you can only register a 'struct request' on a blk_plug, and md doesn't make any use of 'struct request'. As I said in the Email you quote above: > > Therefore md cannot put anything useful on the list in 'struct blk_plug'. That is the heart of the problem. NeilBrown -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
