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. :-) -- 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
