[PATCH] SGI 905314 (2/2): document constraints on client transfer size

[Greg Banks <gnb@melbourne.sgi.com>]

G'day,

SGI bug #905314

This patch adds a comment documenting the actual constraints
on NFS_MAX_FILE_IO_BUFFER_SIZE for the next guy who needs to know ;-)

--- /usr/tmp/TmpDir.28396-0/linux/linux/include/linux/nfs_fs.h_1.21	Fri Nov 28
23:07:47 2003
+++ linux/include/linux/nfs_fs.h	Fri Nov 28 21:55:30 2003
@@ -40,6 +40,18 @@
  */
 #define NFS_MAX_DIRCACHE		16
 
+/* 
+ * NFS_MAX_FILE_IO_BUFFER_SIZE limits the rsize and wsize that
+ * userspace can request in mount options (note that the server
+ * also gives us a limit in response to the FSINFO call).  The
+ * value is constrained by 1) has to fit in a UDP datagram less
+ * some headers 2) has to be a multiple of page size 3) has to
+ * be no more than NFS_READ_MAXIOV=8 pages for rsize, and
+ * NFS_WRITE_MAXIOV=8 pages for wsize and 4) has to be a power
+ * of two (actually this is bogus but nfs_read_super relies on it).
+ * For best performance we usually want the largest value
+ * consistent with these constraints.
+ */
 #define NFS_MAX_FILE_IO_BUFFER_SIZE	32768
 #define NFS_DEF_FILE_IO_BUFFER_SIZE	4096
 



Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.


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