On Wed, Jan 7, 2015 at 5:11 PM, Tom Haynes <thomas.haynes@xxxxxxxxxxxxxxx> wrote: > Adding NFSv4 WG .... > > On Wed, Jan 07, 2015 at 04:05:43PM -0800, Trond Myklebust wrote: >> On Wed, Jan 7, 2015 at 12:04 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: >> > Hi- >> > >> > Dai noticed that when a 3.17 Linux NFS client is granted a > > Hi, is this new behavior for 3.17 or does it happen to prior > versions as well? > >> > write delegation, it neglects to flush dirty data synchronously >> > with close(2). The data is flushed asynchronously, and close(2) >> > completes immediately. Normally that’s OK. But Dai observed that: >> > >> > 1. If the server can’t accommodate the dirty data (eg ENOSPC or >> > EIO) the application is not notified, even via close(2) return >> > code. >> > >> > 2. If the server is down, the application does not hang, but it >> > can leave dirty data in the client’s page cache with no >> > indication to applications or administrators. >> > >> > The disposition of that data remains unknown even if a umount >> > is attempted. While the server is down, the umount will hang >> > trying to flush that data without giving an indication of why. >> > >> > 3. If a shutdown is attempted while the server is down and there >> > is a pending flush, the shutdown will hang, even though there >> > are no running applications with open files. >> > >> > 4. The behavior is non-deterministic from the application’s >> > perspective. It occurs only if the server has granted a write >> > delegation for that file; otherwise close(2) behaves like it >> > does for NFSv2/3 or NFSv4 without a delegation present >> > (close(2) waits synchronously for the flush to complete). >> > >> > Should close(2) wait synchronously for a data flush even in the >> > presence of a write delegation? >> > >> > It’s certainly reasonable for umount to try hard to flush pinned >> > data, but that makes shutdown unreliable. >> >> We should probably start paying more attention to the "space_limit" >> field in the write delegation. That field is supposed to tell the >> client precisely how much data it is allowed to cache on close(). >> > > Sure, but what does that mean? > > Is the space_limit supposed to be on the file or the amount of data that > can be cached by the client? > > Note that Spencer Dawkins effectively asked this question a couple of years ago: > > | In this text: > | > | 15.18.3. RESULT > | > | nfs_space_limit4 > | space_limit; /* Defines condition that > | the client must check to > | determine whether the > | file needs to be flushed > | to the server on close. */ > | > | I'm no expert, but could I ask you to check whether this is the right > | description for this struct? nfs_space_limit4 looks like it's either > | a file size or a number of blocks, and I wasn't understanding how that > | was a "condition" or how the limit had anything to do with flushing a > | file to the server on close, so I'm wondering about a cut-and-paste error. > | > > Does any server set the space_limit? > > And to what? > > Note, it seems that OpenSolaris does set it to be NFS_LIMIT_SIZE and > UINT64_MAX. Which means that it is effectively saying that the client > is guaranteed a lot of space. :-) Yes... Unless they plan to never return NFS4ERR_NOSPC, then that suggests we should probably file an errata deprecating the feature altogether. -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@xxxxxxxxxxxxxxx -- 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
