On Sat, Jun 08, 2019 at 10:10:36AM +1000, Dave Chinner wrote: > On Fri, Jun 07, 2019 at 11:25:35AM -0700, Ira Weiny wrote: > > On Fri, Jun 07, 2019 at 01:04:26PM +0200, Jan Kara wrote: > > > On Thu 06-06-19 15:03:30, Ira Weiny wrote: > > > > On Thu, Jun 06, 2019 at 12:42:03PM +0200, Jan Kara wrote: > > > > > On Wed 05-06-19 18:45:33, ira.weiny@xxxxxxxxx wrote: > > > > > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > > > > > > > So I'd like to actually mandate that you *must* hold the file lease until > > > > > you unpin all pages in the given range (not just that you have an option to > > > > > hold a lease). And I believe the kernel should actually enforce this. That > > > > > way we maintain a sane state that if someone uses a physical location of > > > > > logical file offset on disk, he has a layout lease. Also once this is done, > > > > > sysadmin has a reasonably easy way to discover run-away RDMA application > > > > > and kill it if he wishes so. > > > > > > > > Fair enough. > > > > > > > > I was kind of heading that direction but had not thought this far forward. I > > > > was exploring how to have a lease remain on the file even after a "lease > > > > break". But that is incompatible with the current semantics of a "layout" > > > > lease (as currently defined in the kernel). [In the end I wanted to get an RFC > > > > out to see what people think of this idea so I did not look at keeping the > > > > lease.] > > > > > > > > Also hitch is that currently a lease is forcefully broken after > > > > <sysfs>/lease-break-time. To do what you suggest I think we would need a new > > > > lease type with the semantics you describe. > > > > > > I'd do what Dave suggested - add flag to mark lease as unbreakable by > > > truncate and teach file locking core to handle that. There actually is > > > support for locks that are not broken after given timeout so there > > > shouldn't be too many changes need. > > > > > > > Previously I had thought this would be a good idea (for other reasons). But > > > > what does everyone think about using a "longterm lease" similar to [1] which > > > > has the semantics you proppose? In [1] I was not sure "longterm" was a good > > > > name but with your proposal I think it makes more sense. > > > > > > As I wrote elsewhere in this thread I think FL_LAYOUT name still makes > > > sense and I'd add there FL_UNBREAKABLE to mark unusal behavior with > > > truncate. > > > > Ok I want to make sure I understand what you and Dave are suggesting. > > > > Are you suggesting that we have something like this from user space? > > > > fcntl(fd, F_SETLEASE, F_LAYOUT | F_UNBREAKABLE); > > Rather than "unbreakable", perhaps a clearer description of the > policy it entails is "exclusive"? > > i.e. what we are talking about here is an exclusive lease that > prevents other processes from changing the layout. i.e. the > mechanism used to guarantee a lease is exclusive is that the layout > becomes "unbreakable" at the filesystem level, but the policy we are > actually presenting to uses is "exclusive access"... That sounds good. Ira > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
