MFC: r273486

Clip the settings for the NFS rsize, wsize mount options
to a power of 2. For non-power of 2 settings, intermittent
page faults have been reported. Although the bug that causes
these page faults/crashes has not been identified, it does
not appear to occur when rsize, wsize is a power of 2.

1 files changed, 16 insertions, 6 deletions

diff --git a/sys/fs/nfsclient/nfs_clvfsops.c b/sys/fs/nfsclient/nfs_clvfsops.c
index 6b09356..4cbbb24 100644
--- a/sys/fs/nfsclient/nfs_clvfsops.c
+++ b/sys/fs/nfsclient/nfs_clvfsops.c
@@ -621,17 +621,27 @@ nfs_decode_args(struct mount *mp, struct nfsmount *nmp, struct nfs_args *argp,
 
 	if ((argp->flags & NFSMNT_WSIZE) && argp->wsize > 0) {
 		nmp->nm_wsize = argp->wsize;
-		/* Round down to multiple of blocksize */
-		nmp->nm_wsize &= ~(NFS_FABLKSIZE - 1);
-		if (nmp->nm_wsize <= 0)
+		/*
+		 * Clip at the power of 2 below the size. There is an
+		 * issue (not isolated) that causes intermittent page
+		 * faults if this is not done.
+		 */
+		if (nmp->nm_wsize > NFS_FABLKSIZE)
+			nmp->nm_wsize = 1 << (fls(nmp->nm_wsize) - 1);
+		else
 			nmp->nm_wsize = NFS_FABLKSIZE;
 	}
 
 	if ((argp->flags & NFSMNT_RSIZE) && argp->rsize > 0) {
 		nmp->nm_rsize = argp->rsize;
-		/* Round down to multiple of blocksize */
-		nmp->nm_rsize &= ~(NFS_FABLKSIZE - 1);
-		if (nmp->nm_rsize <= 0)
+		/*
+		 * Clip at the power of 2 below the size. There is an
+		 * issue (not isolated) that causes intermittent page
+		 * faults if this is not done.
+		 */
+		if (nmp->nm_rsize > NFS_FABLKSIZE)
+			nmp->nm_rsize = 1 << (fls(nmp->nm_rsize) - 1);
+		else
 			nmp->nm_rsize = NFS_FABLKSIZE;
 	}