On Fri, 2009-05-29 at 13:42 -0400, Trond Myklebust wrote: > On Fri, 2009-05-29 at 13:38 -0400, Brian R Cowan wrote: > > > You may have a misunderstanding about what exactly "async" does. The > > > "sync" / "async" mount options control only whether the application > > > waits for the data to be flushed to permanent storage. They have no > > > effect on any file system I know of _how_ specifically the data is > > > moved from the page cache to permanent storage. > > > > The problem is that the client change seems to cause the application to > > stop until this stable write completes... What is interesting is that it's > > not always a write operation that the linker gets stuck on. Our best > > hypothesis -- from correlating times in strace and tcpdump traces -- is > > that the FILE_SYNC'ed write NFS RPCs are in fact triggered by *read()* > > system calls on the output file (that is opened for read/write). We THINK > > the read call triggers a FILE_SYNC write if the page is dirty...and that > > is why the read calls are taking so long. Seeing writes happening when the > > app is waiting for a read is odd to say the least... (In my test, there is > > nothing else running on the Virtual machines, so the only thing that could > > be triggering the filesystem activity is the build test...) > > Yes. If the page is dirty, but not up to date, then it needs to be > cleaned before you can overwrite the contents with the results of a > fresh read. > That means flushing the data to disk... Which again means doing either a > stable write or an unstable write+commit. The former is more efficient > that the latter, 'cos it accomplishes the exact same work in a single > RPC call. > > Trond In fact, I suspect your real gripe is rather with the logic that marks a page as being up to date (i.e. whether or not they require a READ call). I suggest trying kernel 2.6.27 or newer, and seeing if the changes that are in those kernels fix your problem. Trond -- 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
