On Mon, 2016-11-28 at 11:31 -0600, Benjamin Marzinski wrote: > On Mon, Nov 28, 2016 at 11:28:56AM +0100, Martin Wilck wrote: > > On Mon, 2016-11-28 at 10:19 +0800, tang.junhui@xxxxxxxxxx wrote: > > > > > > 4. Proposal > > > Other than processing uevents one by one, uevents which coming > > > from > > > the > > > same LUN devices can be mergered to one, and then uevent > > > processing > > > thread only needs to process it once, and it only produces one DM > > > addition > > > uevent which could reduce system resource consumption. > > > > > > > Here comes an idea how to achieve this without a lot of additional > > code: > > > > libmultipath already has code to check whether any maps need to be > > updated (in coalesce_paths()). Instead of recording uevents, > > merging > > them, and calling ev_add_path() for every affected WWID, it might > > be > > sufficient to set daemon state to DAEMON_CONFIGURE and wake up the > > main > > multipathd thread to call reconfigure(). Then we only need to make > > sure > > that coalesce_paths() really reloads or creates maps only when > > necessary. I have some patches here that I made for that purpose, > > for a > > different scenario (multipathd to avoid RELOAD ioctls when it's > > started > > in a scenario where most paths are already set up by udev). > > There is a long standing multipath issue that this will likely make a > lot worse. Currently, multipathd can drop paths that it doesn't have > access to on reconfigure. This is wrong. When the path comes back, it > won't issue another add uevent. This means that multipathd won't be > able > to re-enable it (since it stopped monitoring it during the > reconfigure). > In fact the only way to get the path back is to either manually > intervene or to have the path actually get removed from the system > and > come back. Thanks for pointing this out. But don't you think it can be dealt with by fixing the reconfigure() path? My point is: any code that merges uevents and tries to figure out the correct "minimal" set DM operations to put the changes in place re- implement at least parts of the logic of coalesce_paths(), and face similar problems. Regards Martin -- Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
