Refine the implementation of POSIX_FADV_NOREUSE for the read(2) case such

that instead of using direct I/O it allows read-ahead similar to
POSIX_FADV_NORMAL, but invokes VOP_ADVISE(POSIX_FADV_DONTNEED) after the
read(2) has completed to purge just-read data.  The write(2) path continues
to use direct I/O for POSIX_FADV_NOREUSE for now.  Note that NOREUSE works
optimally if an application reads and writes full fs blocks.

1 files changed, 7 insertions, 7 deletions

diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index e33592a..f94bc12 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -519,6 +519,7 @@ vn_read(fp, uio, active_cred, flags, td)
 	int error, ioflag;
 	struct mtx *mtxp;
 	int advice, vfslocked;
+	off_t offset;
 
 	KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
 	    uio->uio_td, td));
@@ -558,19 +559,14 @@ vn_read(fp, uio, active_cred, flags, td)
 	switch (advice) {
 	case POSIX_FADV_NORMAL:
 	case POSIX_FADV_SEQUENTIAL:
+	case POSIX_FADV_NOREUSE:
 		ioflag |= sequential_heuristic(uio, fp);
 		break;
 	case POSIX_FADV_RANDOM:
 		/* Disable read-ahead for random I/O. */
 		break;
-	case POSIX_FADV_NOREUSE:
-		/*
-		 * Request the underlying FS to discard the buffers
-		 * and pages after the I/O is complete.
-		 */
-		ioflag |= IO_DIRECT;
-		break;
 	}
+	offset = uio->uio_offset;
 
 #ifdef MAC
 	error = mac_vnode_check_read(active_cred, fp->f_cred, vp);
@@ -587,6 +583,10 @@ vn_read(fp, uio, active_cred, flags, td)
 	}
 	fp->f_nextoff = uio->uio_offset;
 	VOP_UNLOCK(vp, 0);
+	if (error == 0 && advice == POSIX_FADV_NOREUSE &&
+	    offset != uio->uio_offset)
+		error = VOP_ADVISE(vp, offset, uio->uio_offset - 1,
+		    POSIX_FADV_DONTNEED);
 	VFS_UNLOCK_GIANT(vfslocked);
 	return (error);
 }