nfsd write throughput

[Olaf Kirch <okir@suse.de>]

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Hi,

I've been looking at the write throughput with NFSv3, and played around
a little. Here's a patch that seems to increase iozone's write throughput
from 6MB/s to close to 10MB/s on my test machine.

(The improvement in rewrite throughput is less pronounced). I'm still
doing some testing on this, but I would still appreciate some feedback,
especially from people seeing throughput problems.

Olaf
-- 
Olaf Kirch     |  The Hardware Gods hate me.
okir@suse.de   |
---------------+ 

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Index: linux-2.6.5/fs/nfsd/vfs.c
===================================================================
--- linux-2.6.5.orig/fs/nfsd/vfs.c	2004-08-02 14:48:02.000000000 +0200
+++ linux-2.6.5/fs/nfsd/vfs.c	2004-08-02 17:54:28.000000000 +0200
@@ -45,6 +45,7 @@
 #include <linux/quotaops.h>
 #include <linux/dnotify.h>
 #include <linux/xattr_acl.h>
+#include <linux/backing-dev.h>
 
 #include <asm/uaccess.h>
 
@@ -810,6 +811,22 @@
 		}
 		last_ino = inode->i_ino;
 		last_dev = inode->i_sb->s_dev;
+	} else if (err >= 0 && !stable) {
+		/* If we've been writing several pages, schedule them
+		 * for the disk immediately. The client may be streaming
+		 * and we don't want to hang on a huge journal sync when the
+		 * commit comes in
+		 */
+		struct address_space	*mapping;
+
+		/* This assumes a minimum page size of 1K, and will issue
+		 * a filemap_flushfast call every 64 pages written by the
+		 * client. */
+		if ((cnt & 1023) == 0
+		 && ((offset / cnt) & 63) == 0
+		 && (mapping = inode->i_mapping) != NULL
+		 && !bdi_write_congested(mapping->backing_dev_info))
+			filemap_flushfast(mapping);
 	}
 
 	dprintk("nfsd: write complete err=%d\n", err);