Hi. On Tuesday 24 July 2007 01:23:15 Alan Stern wrote: > On Mon, 23 Jul 2007, Nigel Cunningham wrote: > > > Take a step back for a second. > > > > The problem we're facing now is that we're getting some userspace threads, > > used in processing I/O, that are functioning as exceptions to the "freeze > > userspace, then freezeable kernel threads" rule. They are only exceptions > > because of that role in processing I/O - because they're de facto kernel > > threads. So, if we orient our thinking more in terms of I/O processing and > > less in terms of the userspace/kernelspace distinction, we'll have a > > solution: > > > > 1) Freeze processes that aren't fs related (ie stop them generating I/O). > > The problem here is that with things like FUSE, _every_ process is > potentially fs related. Nothing prevents a FUSE thread from doing IPC > with any other thread. Yes, but the fuse thread is going to know what other thread it's doing IPC with, so it can get that thread flagged too. > > 2) Flush pending I/O. > > 3) Freeze filesystems in reverse order of dependency, the primary purpose > > being to stop them generating further I/O on their metadata. > > > > Locks that are being held are only being held because work is being done. If > > we progressively focus on threads in terms of their create/process work > > dependencies, we'll see that the problem isn't at all intractable. > > As has been mentioned before, keeping track of all that dependency > information would be very fragile and time-consuming. I disagree. It's at least going to be less fragile and time-consuming then maintaining new/extra code for kexec. Nigel
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