On Wed, Aug 4, 2010 at 5:52 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > On Wed, 2010-08-04 at 14:40 -0700, Yudong Gao wrote: >> 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... > > No. We didn't do that. The main reason for continuing to flush the > writes on close is to avoid slow delegation recalls. > This makes sense! Thanks for clarifying! >> 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. > > AFAIK fscache is read-only at this point. I think David has plans to > make it read/write, but I don't know whether he will ever do so for NFS. > I think fscache itself support writing. We can find the fscache_write_page() definition in both the api document and the source code. I check the source code and it seems fully implemented. But for the integration with NFS, it is confusing. The fscache_write_page() is called only in one place: nfs_readpage_release(). So a NFS page is only written to fscache after it is read from the server in nfs_readpage. So my question is, if a page is locally modified, when its data is propagated to fscache? I check the nfs_write_begin() and nfs_write_end() but cannot find any relative implementation. Thanks! best, Yudong > Trond > >> 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
