Date: Wed, 4 May 2022 17:53:27 -0600 From: Alan Somers <asomers@freebsd.org> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: FreeBSD Stable ML <stable@freebsd.org> Subject: Re: nfs client's OpenOwner count increases without bounds Message-ID: <CAOtMX2hNp3%2B0Zs1jvpVAW07KLxStX0z-khZ4Y_-GaPnO%2BYkM5g@mail.gmail.com> In-Reply-To: <YT3PR01MB97376472A2BAF2FA0643F4F2DDC39@YT3PR01MB9737.CANPRD01.PROD.OUTLOOK.COM> References: <CAOtMX2jX8gC8xEr%2BfsQjZz8YmWX6haQxRe_-Jr5RSTdw14jkFQ@mail.gmail.com> <YT3PR01MB97376472A2BAF2FA0643F4F2DDC39@YT3PR01MB9737.CANPRD01.PROD.OUTLOOK.COM>
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On Wed, May 4, 2022 at 5:23 PM Rick Macklem <rmacklem@uoguelph.ca> wrote: > > Alan Somers <asomers@freebsd.org> wrote: > > I have a FreeBSD 13 (tested on both 13.0-RELEASE and 13.1-RC5) desktop > > mounting /usr/home over NFS 4.2 from an 13.0-RELEASE server. It > > worked fine until a few weeks ago. Now, the desktop's performance > > slowly degrades. It becomes less and less responsive until I restart > > X after 2-3 days. /var/log/Xorg.0.log shows plenty of entries like > > "AT keyboard: client bug: event processing lagging behind by 112ms, > > your system is too slow". "top -S" shows that the busiest process is > > nfscl. A dtrace profile shows that nfscl is spending most of its time > > in nfscl_cleanup_common, in the loop over all nfsclowner objects. > > Running "nfsdumpstate" on the server shows thousands of OpenOwners for > > that client, and < 10 for any other NFS client. The OpenOwners > > increases by about 3000 per day. And yet, "fstat" shows only a couple > > hundred open files on the NFS file system. Why are OpenOwners so > > high? Killing most of my desktop processes doesn't seem to make a > > difference. Restarting X does improve the perceived responsiveness, > > though it does not change the number of OpenOwners. > > > > How can I figure out which process(es) are responsible for the > > excessive OpenOwners? > An OpenOwner represents a process on the client. The OpenOwner > name is an encoding of pid + process startup time. > However, I can't think of an easy way to get at the OpenOwner name. > > Now, why aren't they going away, hmm.. > > I'm assuming the # of Opens is not large? > (Openowners cannot go away until all associated opens > are closed.) Oh, I didn't mention that yes the number of Opens is large. Right now, for example, I have 7950 OpenOwner and 8277 Open. > > Commit 1cedb4ea1a79 in main changed the semantics of this > a little, to avoid a use-after-free bug. However, it is dated > Feb. 25, 2022 and is not in 13.0, so I don't think it could > be the culprit. > > Essentially, the function called nfscl_cleanupkext() should call > nfscl_procdoesntexist(), which returns true after the process has > exited and when that is the case, calls nfscl_cleanup_common(). > --> nfscl_cleanup_common() will either get rid of the openowner or, > if there are still children with open file descriptors, mark it "defunct" > so it can be free'd once the children close the file. > > It could be that X is now somehow creating a long chain of processes > where the children inherit a file descriptor and that delays the cleanup > indefinitely? > Even then, everything should get cleaned up once you kill off X? > (It might take a couple of seconds after killing all the processes off.) > > Another possibility is that the "nfscl" thread is wedged somehow. > It is the one that will call nfscl_cleanupkext() once/sec. If it never > gets called, the openowners will never go away. > > Being old fashioned, I'd probably try to figure this out by adding > some printf()s to nfscl_cleanupkext() and nfscl_cleanup_common(). dtrace shows that nfscl_cleanupkext() is getting called at about 0.6 hz. > > To avoid the problem, you can probably just use the "oneopenown" > mount option. With that option, only one openowner is used for > all opens. (Having separate openowners for each process was needed > for NFSv4.0, but not NFSv4.1/4.2.) > > > Or is it just a red herring and I shouldn't > > worry? > Well, you can probably avoid the problem by using the "oneopenown" > mount option. Ok, I'm trying that now. After unmounting and remounting NFS, "nfsstat -cE" reports 1 OpenOwner and 11 Opens". But on the server, "nfsdumpstate" still reports thousands. Will those go away eventually? > > Thanks for reporting this, rick > ps: And, yes, large numbers of openowners will slow things down, > since the code ends up doing linear scans of them all in a linked > list in various places. > > -Alan >
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