On Mon, Jan 06 2020 at 4:52pm -0500, Khazhismel Kumykov <khazhy@xxxxxxxxxx> wrote: > On Mon, Jan 6, 2020 at 11:28 AM Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > On Thu, Jan 02 2020 at 5:45pm -0500, > > Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> wrote: > > > > > From: Anatol Pomazau <anatol@xxxxxxxxxx> > > > > > > Add a configurable timeout mechanism to disable queue_if_no_path without > > > assistance from multipathd. In reality, this reimplements the > > > no_path_retry mechanism from multipathd in kernel space, which is > > > interesting for cases where we cannot rely on a daemon being present all > > > the time, in case of failure or to reduce the guest footprint of cloud > > > services. > > > > > > Despite replicating the policy configuration on kernel space, it is > > > quite an important case to prevent IOs from hanging forever, waiting for > > > userspace to behave correctly. > > > > > > Co-developed-by: Frank Mayhar <fmayhar@xxxxxxxxxx> > > > Signed-off-by: Frank Mayhar <fmayhar@xxxxxxxxxx> > > > Co-developed-by: Bharath Ravi <rbharath@xxxxxxxxxx> > > > Signed-off-by: Bharath Ravi <rbharath@xxxxxxxxxx> > > > Co-developed-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx> > > > Signed-off-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx> > > > Signed-off-by: Anatol Pomazau <anatol@xxxxxxxxxx> > > > Co-developed-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> > > > Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> > > > > This seems like a slippery slope. > > > > I've heard this line of dm-multipath concern from Google before > > (e.g. doesn't want to rely on availability of userspace component). > > > > Thing is, to properly use dm-multipath (e.g. to reinstate failed paths) > > multipathd really is needed no? > Yeah, in order to reinstate the failed paths, or any full recovery, we > do need the user space component to be running, and this doesn't aim > to change the responsibilities here. Rather, we're aiming to avoid > in-kernel hangs/processes lingering indefinitely in unkillable sleep > due to buggy/unavailable/down userspace multipath daemon. Sorry but the above patch header clearly states: "or to reduce the guest footprint of cloud services" Which implies that multipathd isn't available by design in the referenced environment. > > > > If not, how is it that the proposed patch is all that is missing when > > multipathd isn't running? I find that hard to appreciate. > > > > So I'm inclined to not accept this type of change. But especially not > > until more comprehensive context is given for how Google is using > > dm-multipath without multipathd. > > This patch isn't aimed at enabling dm-multipath without a userspace > multipath daemon, rather to avoid processes hanging indefinitely in > the event the daemon is unable to proceed (for whatever reason). Again, I don't buy it given the patch header explicitly says dm-multipath could be deployed in the cloud without the benefit of multipathd running. But I'll meet you half-way to start: rather than make the timeout configurable on a per multipath table basis, please just set a longer stopgap default and allow that timeout value to be configured with a module parameter (e.g. dm_multipath.queue_if_no_path_timeout=120, and setting it to 0 disables the timeout). This would follow the same pattern that was established by DM thin-provisioning's no_space_timeout modparm with these commits: 85ad643b dm thin: add timeout to stop out-of-data-space mode holding IO forever 80c57893 dm thin: add 'no_space_timeout' dm-thin-pool module param That'd save us from having to do a bunch of fiddley DM multpath table parsing for now. But if for some crazy reason in the future it is determined that a longer duration stop-gap timeout cannot be one-size-fits-all we can layer per device configuration in at that time. How does that sound? Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
