I see. But according to the spec, the write delegation is supposed to break the close-to-open consistency so that the client can avoid flushing dirty page to server when closing the file. Is this part implemented? I can not find it in the source code... Another question is how the nfs file write interacts with fscache? I was not able to find the code that update the page copy in fscache when the page in memory is modified. Thanks a lot! best, Yudong On Wed, Aug 4, 2010 at 2:22 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > On Wed, 2010-08-04 at 14:11 -0700, Yudong Gao wrote: >> Thanks for the reply, Andy! >> >> So the write delegation can only reduce the unnecessary open/close and >> lock/locku. But if a client modify the same page for multiple times, >> e.g. editing the file in a editor, is there any optimization to >> prevent the client from sending the half-updated pages? Ideally only >> the final update need to be put on the wire. >> > > Yes. However that optimisation is not linked to whether or not we hold a > write delegation. The NFS client assumes close-to-open cache > consistency, and so will cache writes until either the VM tries to > reclaim memory by writing out dirty page, or the application calls one > of fcntl(F_UNLCK), fsync() or close(). > > Trond > >> Thanks! >> >> best, >> >> Yudong >> >> On Wed, Aug 4, 2010 at 1:59 PM, Andy Adamson <andros@xxxxxxxxxx> wrote: >> > >> > On Aug 4, 2010, at 3:21 PM, Yudong Gao wrote: >> > >> >> Hi, >> >> >> >> I am not able to find the implementation of directory delegation, >> >> either. Similarly, the callback functions CB_NOTIFY is not >> >> implemented, either. I find that in preprocss_nfs41_op() in >> >> callback_xdr.c, whenever a CB_NOTIFY is encountered, an >> >> NFS4ERR_NOTSUPP is returned directly. >> > >> > CB_NOTIFY is not currently supported on the Linux NFS client. >> > >> >> >> >> Am I missing something? Or they are just not supported in the current version? >> >> >> >> Thanks a lot! >> >> >> >> best, >> >> >> >> Yudong >> >> >> >> On Mon, Aug 2, 2010 at 5:17 PM, Yudong Gao <stgyd@xxxxxxxxx> wrote: >> >>> Hi, >> >>> >> >>> I am looking at the delegation implementation in the source code of >> >>> NFS 4.1 in kernel 2.6.32.15. I can find the code for read delegation, >> >>> which is working and can serve the read requests locally. But I can >> >>> never find the code about write delegation, which is supposed to cache >> >>> the write update locally. I try to look at the functions including >> >>> nfs_writepage(s), nfs_file_flush() but none of them checks or uses the >> >>> write delegation. >> >>> >> >>> Is write delegation currently implemented in NFS 4.1? >> > >> > Write delegation is supported but I don't think write behavior changes - writes are still cached and flushed as without a write delegation. The write delegation does prevent open/close and lock/locku from being put on the wire. >> > >> > -->Andy >> > >> >>> >> >>> Thanks! >> >>> >> >>> best, >> >>> >> >>> Yudong >> >>> >> >> -- >> >> 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 >> > >> > >> -- >> 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 > > > > -- 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
