----- Original Message ---- > From: Chuck Lever <chucklever@xxxxxxxxx> > To: Martin Knoblauch <knobi@xxxxxxxxxxxx> > Cc: Peter Staubach <staubach@xxxxxxxxxx>; linux-nfs list <linux-nfs@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx > Sent: Wednesday, September 17, 2008 6:43:48 PM > Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable > > On Wed, Sep 17, 2008 at 11:23 AM, Martin Knoblauch wrote: > > ----- Original Message ---- > > > >> From: Chuck Lever > >> To: Peter Staubach > >> Cc: Martin Knoblauch ; linux-nfs list > ; linux-kernel@xxxxxxxxxxxxxxx > >> Sent: Wednesday, September 17, 2008 5:41:15 PM > >> Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable > >> > >> On Wed, Sep 17, 2008 at 9:06 AM, Peter Staubach wrote: > >> > Martin Knoblauch wrote: > >> >> > >> >> Hi, > >> >> > >> >> the following/attached patch works around a [obscure] problem when an 2.6 > >> >> (not sure/caring about 2.4) NFS client accesses an "offline" file on a > >> >> Sun/Solaris-10 NFS server when the underlying filesystem is of type > SAM-FS. > >> >> Happens with RHEL4/5 and mainline kernels. Frankly, it is not a Linux > >> >> problem, but the chance for a short-/mid-term solution from Sun are very > >> >> slim. So, being lazy, I would love to get this patch into Linux. If not, I > >> >> just will have to maintain it for eternity out of tree. > >> >> > >> >> The problem: SAM-FS is Suns proprietary HSM filesystem. It stores > >> >> meta-data and a relatively small amount of data "online" on disk and > pushes > >> >> old or infrequently used data to "offline" media like e.g. tape. This is > >> >> completely transparent to the users. If the date for an "offline" file is > >> >> needed, the so called "stager daemon" copies it back from the offline > >> >> medium. All of this works great most of the time. Now, if an Linux NFS > >> >> client tries to read such an offline file, performance drops to "extremely > >> >> slow". After lengthly investigation of tcp-dumps, mount options and > >> >> procedures involving black cats at midnight, we found out that the > readahead > >> >> behaviour of the Linux NFS client causes the problem. Basically it seems > to > >> >> issue read requests up to 15*rsize to the server. In the case of the > >> >> "offline" files, this behaviour causes heavy competition for the inode > lock > >> >> between the NFSD process and the stager daemon on the Solaris server. > >> >> > >> >> - The real solution: fixing SAM-FS/NFSD interaction. Sun engineering acks > >> >> the problem, but a solution will need time. Lots of it. > >> >> - The working solution: disable the client side readahead, or make it > >> >> tunable. The patch does that by introducing a NFS module parameter > >> >> "ra_factor" which can take values between 1 and 15 (default 15) and a > >> >> tunable "/proc/sys/fs/nfs/nfs_ra_factor" with the same range and default. > >> > > >> > Hi. > >> > > >> > I was curious if a design to limit or eliminate read-ahead > >> > activity when the server returns EJUKEBOX was considered? > >> > Unless one can know that the server and client can get into > >> > this situation ahead of time, how would the tunable be used? > >> > >> I tend to agree. A tunable is probably not a good solution in this case. > >> > >> I would bet that this lock contention issue is a problem in other more > >> common cases, and would merit some careful analysis. > >> > > > > Are you talking wrt. a Solaris NFS-Server with SAM-FS/QFS as backend > filesystem? > > I misread your mail, and thought the inode lock contention issue was > on the client. > No problem, maybe I was not articulating myself clearly. Just to restate - the lock contention happens on the server. Cheers Martin -- 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
