Mike Snitzer <snitzer@xxxxxxxxxx> writes: > 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. Hey Mike, I believe that was my fault, I misunderstood the google's use case, when I modified the commit message. > 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? That seems reasonable to me. Let me see what Khazhismel thinks and I can follow up with a v2. -- Gabriel Krisman Bertazi -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
