On Sat, 2017-03-11 at 11:53 -0500, Chuck Lever wrote: > Hi Bruce, Jeff- > > I've observed some interesting Linux NFS server behavior (v4.1.12). > > We have a single system that has an NFSv4 mount via the kernel NFS > client, and an NFSv3 mount of the same export via a user space NFS > client. These two clients are accessing the same set of files. > > The following pattern is seen on the wire. I've filtered a recent > capture on the FH of one of the shared files. > > ---- cut here ---- > > 18507 19.483085 10.0.2.11 -> 10.0.1.8 NFS 238 V4 Call ACCESS FH: 0xc930444f, [Check: RD MD XT XE] > 18508 19.483827 10.0.1.8 -> 10.0.2.11 NFS 194 V4 Reply (Call In 18507) ACCESS, [Access Denied: XE], [Allowed: RD MD XT] > 18510 19.484676 10.0.1.8 -> 10.0.2.11 NFS 434 V4 Reply (Call In 18509) OPEN StateID: 0x6de3 > > This OPEN reply offers a read delegation to the kernel NFS client. > > 18511 19.484806 10.0.2.11 -> 10.0.1.8 NFS 230 V4 Call GETATTR FH: 0xc930444f > 18512 19.485549 10.0.1.8 -> 10.0.2.11 NFS 274 V4 Reply (Call In 18511) GETATTR > 18513 19.485611 10.0.2.11 -> 10.0.1.8 NFS 230 V4 Call GETATTR FH: 0xc930444f > 18514 19.486375 10.0.1.8 -> 10.0.2.11 NFS 186 V4 Reply (Call In 18513) GETATTR > 18515 19.486464 10.0.2.11 -> 10.0.1.8 NFS 254 V4 Call CLOSE StateID: 0x6de3 > 18516 19.487201 10.0.1.8 -> 10.0.2.11 NFS 202 V4 Reply (Call In 18515) CLOSE > 18556 19.498617 10.0.2.11 -> 10.0.1.8 NFS 210 V3 READ Call, FH: 0xc930444f Offset: 8192 Len: 8192 > > This READ call by the user space client does not conflict with the > read delegation. > > 18559 19.499396 10.0.1.8 -> 10.0.2.11 NFS 8390 V3 READ Reply (Call In 18556) Len: 8192 > 18726 19.568975 10.0.1.8 -> 10.0.2.11 NFS 310 V3 LOOKUP Reply (Call In 18725), FH: 0xc930444f > 18727 19.569170 10.0.2.11 -> 10.0.1.8 NFS 210 V3 READ Call, FH: 0xc930444f Offset: 0 Len: 512 > 18728 19.569923 10.0.1.8 -> 10.0.2.11 NFS 710 V3 READ Reply (Call In 18727) Len: 512 > 18729 19.570135 10.0.2.11 -> 10.0.1.8 NFS 234 V3 SETATTR Call, FH: 0xc930444f > 18730 19.570901 10.0.1.8 -> 10.0.2.11 NFS 214 V3 SETATTR Reply (Call In 18729) Error: NFS3ERR_JUKEBOX > > The user space client has attempted to extend the file. This does > conflict with the read delegation held by the kernel NFS client, > so the server returns JUKEBOX, the equivalent of NFS4ERR_DELAY. > This causes a negative performance impact on the user space NFS > client. > > 18731 19.575396 10.0.2.11 -> 10.0.1.8 NFS 250 V4 Call DELEGRETURN StateID: 0x6de3 > 18732 19.576132 10.0.1.8 -> 10.0.2.11 NFS 186 V4 Reply (Call In 18731) DELEGRETURN > > No CB_RECALL was done to trigger this DELEGRETURN. Apparently > the application that was accessing this file via the kernel OS > client decided already that it no longer needed the file before > the server could send the CB_RECALL. Sign of perhaps a race > between the applications accessing the file via these two > mounts. > > ---- cut here ---- > > The server is aware of non-NFSv4 accessors of this file in frame > 18556. NFSv3 has no OPEN operation, of course, so it's not > possible for the server to determine how the NFSv3 client will > subsequently access this file. > Right. Why should we assume that the v3 client will do anything other than read there? If we recall the delegation just for reads, then we potentially negatively affect the performance of the v4 client. > Seems like at frame 18556, it would be a best practice to recall > the delegation to avoid potential future conflicts, such as the > SETATTR in frame 18729. > > Or, perhaps that READ isn't the first NFSv3 access of that file. > After all, a LOOKUP would have to be done to retrieve that file's > FH. The OPEN in frame 18556 perhaps could have avoided offering > the READ delegation, knowing there is a recent non-NFSv4 accessor > of that file. > > Would these be difficult or inappropriate policies to implement? > > Reads are not currently considered to be conflicting access vs. a read delegation. I think that's the correct thing to do. Until we have some sort of conflicting behavior I don't see why you'd want to prematurely recall the delegation. Note that we do have a bloom filter now that prevents us from handing out a delegation on a file that was recently recalled. Does that help at all here? -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
