On Fri, Jan 10, 2020 at 11:38 AM Gabriel Krisman Bertazi <kris...@collabora.com> wrote: > > Mike Snitzer <snit...@redhat.com> writes: > > > On Mon, Jan 06 2020 at 4:52pm -0500, > > Khazhismel Kumykov <kha...@google.com> wrote: > > > >> On Mon, Jan 6, 2020 at 11:28 AM Mike Snitzer <snit...@redhat.com> wrote: > >> > > >> > On Thu, Jan 02 2020 at 5:45pm -0500, > >> > Gabriel Krisman Bertazi <kris...@collabora.com> wrote: > >> > > >> > > From: Anatol Pomazau <ana...@google.com> > >> > > > >> > > 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 <fmay...@google.com> > >> > > Signed-off-by: Frank Mayhar <fmay...@google.com> > >> > > Co-developed-by: Bharath Ravi <rbhar...@google.com> > >> > > Signed-off-by: Bharath Ravi <rbhar...@google.com> > >> > > Co-developed-by: Khazhismel Kumykov <kha...@google.com> > >> > > Signed-off-by: Khazhismel Kumykov <kha...@google.com> > >> > > Signed-off-by: Anatol Pomazau <ana...@google.com> > >> > > Co-developed-by: Gabriel Krisman Bertazi <kris...@collabora.com> > >> > > Signed-off-by: Gabriel Krisman Bertazi <kris...@collabora.com> > >> > > >> > 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.
ditto, not trying to mislead, just clear up the misunderstanding :) > > 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. Modparam sounds good to me. As far as we've seen, one size does fit all, so we can drop the unneeded parsing. Thanks, Khazhy
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