On 01/06/2014 05:32 PM, J. Bruce Fields wrote: > On Mon, Jan 06, 2014 at 04:57:10PM -0500, Anna Schumaker wrote: >> These patches are my initial implementation of READ_PLUS. I still have a >> few issues to work out before they can be applied, but I wanted to submit >> them anyway to get feedback before going much further. These patches were >> developed on top of my earlier SEEK and WRITE_PLUS patches, and probably >> won't apply cleanly without them (I am willing to reorder things if necessary!). >> >> On the server side, I handle the cases where a file is 100% hole, 100% data >> or hole followed by data. Any holes after a data segment will be expanded >> to zeros on the wire. > > I assume that for "a file" I should read "the requested range of the > file"? Yes. > > hole+data+hole should also be doable, shouldn't it? I'd think the real > problem would be multiple data extents. It might be, but I haven't tried it yet. I can soon! > >> This is due to a limitation in the the NFSD >> encode-to-page function that will adjust pointers to point to the xdr tail >> after reading a file to the "pages" section. Bruce, do you have any >> suggestions here? > > The server xdr encoding needs a rewrite. I'll see if I can ignore you > all and put my head down and get a version of that posted this week. :) > > That should make it easier to return all the data, though it will turn > off zero-copy in the case of multiple data extents. > > If we want READ_PLUS to support zero copy in the case of multiple > extents then I think we need a new data structure to represent the > resulting rpc reply. An xdr buf only knows how to insert one array of > pages in the middle of the data. Maybe a list of xdr bufs? > > But that's an annoying job and possibly a premature optimization. > > It might be useful to first understand the typical distribution of holes > in a file and how likely various workloads are to produce reads with > multiple holes in the middle. I already have a few performance numbers, but nothing that can be trusted due to the number of debugging printk()s I used to make sure the client decoded everything correctly. My plan is to collect the following information using: v4.0, v4.1, v4.2 (SEEK), v4.2 (SEEK + WRITE_PLUS), and v4.2 (SEEK + WRITE_PLUS + READ_PLUS). Anna > > --b. > >> >> The client side needs to punch holes after decoding page information, since >> data on pages will be aligned at the start of the page array. So a file that >> is <HOLE><DATA> will store the hole information, decode the data, and then >> punch the hole before returning. I think it would be better to use the >> provided offset field to decode everything to their final locations, but I'm >> struggling to come up with a clean way of doing so using the code that is >> already there. >> >> Let me know what you all think! >> Anna >> >> Anna Schumaker (3): >> NFSD: Implement READ_PLUS support >> SUNRPC: This patch adds functions for shifting page data >> NFS: Client side changes for READ_PLUS >> >> fs/nfs/nfs4client.c | 2 +- >> fs/nfs/nfs4proc.c | 23 +++++- >> fs/nfs/nfs4xdr.c | 191 +++++++++++++++++++++++++++++++++++++++++++++ >> fs/nfsd/Kconfig | 14 ++++ >> fs/nfsd/nfs4proc.c | 9 +++ >> fs/nfsd/nfs4xdr.c | 177 ++++++++++++++++++++++++++++++++++++----- >> include/linux/nfs4.h | 1 + >> include/linux/nfs_fs_sb.h | 1 + >> include/linux/sunrpc/xdr.h | 1 + >> net/sunrpc/xdr.c | 115 ++++++++++++++++++++++++++- >> 10 files changed, 511 insertions(+), 23 deletions(-) >> >> -- >> 1.8.5.2 >> -- 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
