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 > 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(). -- 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
