Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 1 Nov 2023 12:23:44 -1000 | Subject | Re: [PATCH RFC 2/9] timekeeping: new interfaces for multigrain timestamp handing |
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On Wed, Nov 1, 2023, 11:35 Trond Myklebust <trondmy@hammerspace.com> wrote: > > My client writes to the file and immediately reads the ctime. A 3rd > party client then writes immediately after my ctime read. > A reboot occurs (maybe minutes later), then I re-read the ctime, and > get the same value as before the 3rd party write. > > Yes, most of the time that is better than the naked ctime, but not > across a reboot.
Ahh, I knew I was missing something.
But I think it's fixable, with an additional rule:
- when generating STATX_CHANGE_COOKIE, if the ctime matches the current time and the ctime counter is zero, set the ctime counter to 1.
That means that you will have *spurious* cache invalidations of such cached data after a reboot, but only for reads that happened right after the file was written.
Now, it's obviously not unheard of to finish writing a file, and then immediately reading the results again.
But at least those caches should be somewhat limited (and the problem then only happens when the nfs server is rebooted).
I *assume* that the whole thundering herd issue with lots of clients tends to be for stable files, not files that were just written and then immediately cached?
I dunno. I'm sure there's still some thinko here.
Linus
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