Add the posix_fadvise(2) system call. It is somewhat similar to

madvise(2) except that it operates on a file descriptor instead of a
memory region.  It is currently only supported on regular files.

Just as with madvise(2), the advice given to posix_fadvise(2) can be
divided into two types.  The first type provide hints about data access
patterns and are used in the file read and write routines to modify the
I/O flags passed down to VOP_READ() and VOP_WRITE().  These modes are
thus filesystem independent.  Note that to ease implementation (and
since this API is only advisory anyway), only a single non-normal
range is allowed per file descriptor.

The second type of hints are used to hint to the OS that data will or
will not be used.  These hints are implemented via a new VOP_ADVISE().
A default implementation is provided which does nothing for the WILLNEED
request and attempts to move any clean pages to the cache page queue for
the DONTNEED request.  This latter case required two other changes.
First, a new V_CLEANONLY flag was added to vinvalbuf().  This requests
vinvalbuf() to only flush clean buffers for the vnode from the buffer
cache and to not remove any backing pages from the vnode.  This is
used to ensure clean pages are not wired into the buffer cache before
attempting to move them to the cache page queue.  The second change adds
a new vm_object_page_cache() method.  This method is somewhat similar to
vm_object_page_remove() except that instead of freeing each page in the
specified range, it attempts to move clean pages to the cache queue if
possible.

To preserve the ABI of struct file, the f_cdevpriv pointer is now reused
in a union to point to the currently active advice region if one is
present for regular files.

Reviewed by:	jilles, kib, arch@
Approved by:	re (kib)
MFC after:	1 month

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index 4cb6633d4cc8..7382336623fe 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -384,6 +384,7 @@ extern int		vttoif_tab[];
 #define	V_SAVE		0x0001	/* vinvalbuf: sync file first */
 #define	V_ALT		0x0002	/* vinvalbuf: invalidate only alternate bufs */
 #define	V_NORMAL	0x0004	/* vinvalbuf: invalidate only regular bufs */
+#define	V_CLEANONLY	0x0008	/* vinvalbuf: invalidate only clean bufs */
 #define	REVOKEALL	0x0001	/* vop_revoke: revoke all aliases */
 #define	V_WAIT		0x0001	/* vn_start_write: sleep for suspend */
 #define	V_NOWAIT	0x0002	/* vn_start_write: don't sleep for suspend */
@@ -685,6 +686,7 @@ int	vop_stdunlock(struct vop_unlock_args *);
 int	vop_nopoll(struct vop_poll_args *);
 int	vop_stdaccess(struct vop_access_args *ap);
 int	vop_stdaccessx(struct vop_accessx_args *ap);
+int	vop_stdadvise(struct vop_advise_args *ap);
 int	vop_stdadvlock(struct vop_advlock_args *ap);
 int	vop_stdadvlockasync(struct vop_advlockasync_args *ap);
 int	vop_stdadvlockpurge(struct vop_advlockpurge_args *ap);