On Fri, 2022-05-20 at 21:52 +0000, Chuck Lever III wrote: > > > > On May 20, 2022, at 12:40 PM, Trond Myklebust > > <trondmy@xxxxxxxxxxxxxxx> wrote: > > > > On Fri, 2022-05-20 at 15:36 +0000, Chuck Lever III wrote: > > > > > > > > > > On May 11, 2022, at 10:36 AM, Chuck Lever III > > > > <chuck.lever@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > On May 11, 2022, at 10:23 AM, Greg KH > > > > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Wed, May 11, 2022 at 02:16:19PM +0000, Chuck Lever III > > > > > wrote: > > > > > > > > > > > > > > > > > > > On May 11, 2022, at 8:38 AM, Greg KH > > > > > > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > On Wed, May 11, 2022 at 12:03:13PM +0200, Wolfgang Walter > > > > > > > wrote: > > > > > > > > Hi, > > > > > > > > > > > > > > > > starting with 5.4.188 wie see a massive performance > > > > > > > > regression on our > > > > > > > > nfs-server. It basically is serving requests very very > > > > > > > > slowly with cpu > > > > > > > > utilization of 100% (with 5.4.187 and earlier it is > > > > > > > > 10%) so > > > > > > > > that it is > > > > > > > > unusable as a fileserver. > > > > > > > > > > > > > > > > The culprit are commits (or one of it): > > > > > > > > > > > > > > > > c32f1041382a88b17da5736886da4a492353a1bb "nfsd: cleanup > > > > > > > > nfsd_file_lru_dispose()" > > > > > > > > 628adfa21815f74c04724abc85847f24b5dd1645 "nfsd: > > > > > > > > Containerise filecache > > > > > > > > laundrette" > > > > > > > > > > > > > > > > (upstream 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63 and > > > > > > > > 9542e6a643fc69d528dfb3303f145719c61d3050) > > > > > > > > > > > > > > > > If I revert them in v5.4.192 the kernel works as before > > > > > > > > and > > > > > > > > performance is > > > > > > > > ok again. > > > > > > > > > > > > > > > > I did not try to revert them one by one as any > > > > > > > > disruption > > > > > > > > of our nfs-server > > > > > > > > is a severe problem for us and I'm not sure if they are > > > > > > > > related. > > > > > > > > > > > > > > > > 5.10 and 5.15 both always performed very badly on our > > > > > > > > nfs- > > > > > > > > server in a > > > > > > > > similar way so we were stuck with 5.4. > > > > > > > > > > > > > > > > I now think this is because of > > > > > > > > 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63 > > > > > > > > and/or 9542e6a643fc69d528dfb3303f145719c61d3050 though > > > > > > > > I > > > > > > > > didn't tried to > > > > > > > > revert them in 5.15 yet. > > > > > > > > > > > > > > Odds are 5.18-rc6 is also a problem? > > > > > > > > > > > > We believe that > > > > > > > > > > > > 6b8a94332ee4 ("nfsd: Fix a write performance regression") > > > > > > > > > > > > addresses the performance regression. It was merged into > > > > > > 5.18- > > > > > > rc. > > > > > > > > > > And into 5.17.4 if someone wants to try that release. > > > > > > > > I don't have a lot of time to backport this one myself, so > > > > I welcome anyone who wants to apply that commit to their > > > > favorite LTS kernel and test it for us. > > > > > > > > > > > > > > > If so, I'll just wait for the fix to get into Linus's > > > > > > > tree as > > > > > > > this does > > > > > > > not seem to be a stable-tree-only issue. > > > > > > > > > > > > Unfortunately I've received a recent report that the fix > > > > > > introduces > > > > > > a "sleep while spinlock is held" for NFSv4.0 in rare cases. > > > > > > > > > > Ick, not good, any potential fixes for that? > > > > > > > > Not yet. I was at LSF last week, so I've just started digging > > > > into this one. I've confirmed that the report is a real bug, > > > > but we still don't know how hard it is to hit it with real > > > > workloads. > > > > > > We believe the following, which should be part of the first > > > NFSD pull request for 5.19, will properly address the splat. > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/commit/?h=for-next&id=556082f5e5d7ecfd0ee45c3641e2b364bff9ee44 > > > > > > > > Uh... What happens if you have 2 simultaneous calls to > > nfsd4_release_lockowner() for the same file? i.e. 2 separate > > processes > > owned by the same user, both locking the same file. > > > > Can't that cause the 'putlist' to get corrupted when both callers > > add > > the same nf->nf_putfile to two separate lists? > > IIUC, cl_lock serializes the two RELEASE_LOCKOWNER calls. > > The first call finds the lockowner in cl_ownerstr_hashtbl and > unhashes it before releasing cl_lock. > > Then the second cannot find that lockowner, thus it can't > requeue it for bulk_put. > > Am I missing something? In the example I quoted, there are 2 separate processes running on the client. Those processes could share the same open owner + open stateid, and hence the same struct nfs4_file, since that depends only on the process credentials matching. However they will not normally share a lock owner, since POSIX does not expect different processes to share locks. IOW: The point is that one can relatively easily create 2 different lock owners with different lock stateids that share the same underlying struct nfs4_file. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx