Index: sys/kern/vfs_vnops.c
===================================================================
--- sys/kern/vfs_vnops.c
+++ sys/kern/vfs_vnops.c
@@ -3263,13 +3263,13 @@
 			len = savlen = rounddown(len - rem, blksize) + rem;
 	}
 
-	if (blksize <= 1)
+	if (blksize <= 512)
 		blksize = MAX(invp->v_mount->mnt_stat.f_iosize,
 		    outvp->v_mount->mnt_stat.f_iosize);
 	if (blksize < 4096)
 		blksize = 4096;
-	else if (blksize > 1024 * 1024)
-		blksize = 1024 * 1024;
+	else if (blksize > maxphys)
+		blksize = maxphys;
 	dat = malloc(blksize, M_TEMP, M_WAITOK);
 
 	/*
@@ -3378,7 +3378,7 @@
 		}
 
 		xfer = blksize;
-		if (cantseek) {
+		if (__predict_false(cantseek)) {
 			/*
 			 * Set first xfer to end at a block boundary, so that
 			 * holes are more likely detected in the loop below via