Date: Wed, 4 May 2022 20:51:23 -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: <CAOtMX2gf-qxJkLCdfvXgLnNE_8jQU2-JwZxb-meDYVm0WKFH-A@mail.gmail.com> In-Reply-To: <YT2PR01MB9730E95FC8997CC2A3FE5AEBDDC29@YT2PR01MB9730.CANPRD01.PROD.OUTLOOK.COM> References: <CAOtMX2jX8gC8xEr%2BfsQjZz8YmWX6haQxRe_-Jr5RSTdw14jkFQ@mail.gmail.com> <YT3PR01MB97376472A2BAF2FA0643F4F2DDC39@YT3PR01MB9737.CANPRD01.PROD.OUTLOOK.COM> <CAOtMX2hNp3%2B0Zs1jvpVAW07KLxStX0z-khZ4Y_-GaPnO%2BYkM5g@mail.gmail.com> <YT2PR01MB9730E95FC8997CC2A3FE5AEBDDC29@YT2PR01MB9730.CANPRD01.PROD.OUTLOOK.COM>
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On Wed, May 4, 2022 at 6:56 PM Rick Macklem <rmacklem@uoguelph.ca> wrote: > > Alan Somers <asomers@freebsd.org> wrote: > > 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. > Well, the openowners cannot go away until the opens go away, > so the problem is that the opens are not getting closed. > > Close happens when the v_usecount on the vnode goes to zero. > Something is retaining the v_usecount. One possibility is that most > of the opens are for the same file, but with different openowners. > If that is the case, the "oneopenown" mount option will deal with it. > > Another possibility is that something is retaining a v_usecount > reference on a lot of the vnodes. (This used to happen when a nullfs > mount with caching enabled was on top of the nfs mount.) > I don't know what other things might do that? Yeah, I remember the nullfs problem. But I'm not using nullfs on this computer anymore. Is there any debugging facility that can list vnodes? All I know of is "fstat", and that doesn't show anywhere near the number of NFS Opens. > > > > > > > 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. > That sounds ok. Since there are a lot of opens/openowners, it probably > is getting behind. > > > > > > > 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? > If the opens are gone then, yes, they will go away. They are retained for > a little while so that another Open against the openowner does not need > to recreate the openowner (which also implied an extra RPC to confirm > the openowner in NFSv4.0). > > I think they go away after a few minutes, if I recall correctly. > If the server thinks there are still Opens, then they will not go away. Uh, they aren't going away. It's been a few hours now, and the NFS server still reports the same number of opens and openowners. > > rick > > > > > 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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