This patch implements O_DIRECT about 80% of the way. It takes a patchset

Tor created a while ago, removes the raw I/O piece (that has cache coherency
problems), and adds a buffer cache / VM freeing piece.

Essentially this patch causes O_DIRECT I/O to not be left in the cache, but
does not prevent it from going through the cache, hence the 80%.  For
the last 20% we need a method by which the I/O can be issued directly to
buffer supplied by the user process and bypass the buffer cache entirely,
but still maintain cache coherency.

I also have the code working under -stable but the changes made to sys/file.h
may not be MFCable, so an MFC is not on the table yet.

Submitted by:	tegge, dillon

1 files changed, 23 insertions, 0 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index c1817d5..dc391cb 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1304,6 +1304,29 @@ vm_page_try_to_cache(vm_page_t m)
 }
 
 /*
+ * vm_page_try_to_free()
+ *
+ *	Attempt to free the page.  If we cannot free it, we do nothing.
+ *	1 is returned on success, 0 on failure.
+ */
+int
+vm_page_try_to_free(m)
+	vm_page_t m;
+{
+	if (m->dirty || m->hold_count || m->busy || m->wire_count ||
+	    (m->flags & (PG_BUSY|PG_UNMANAGED))) {
+		return(0);
+	}
+	vm_page_test_dirty(m);
+	if (m->dirty)
+		return(0);
+	vm_page_busy(m);
+	vm_page_protect(m, VM_PROT_NONE);
+	vm_page_free(m);
+	return(1);
+}
+
+/*
  * vm_page_cache
  *
  * Put the specified page onto the page cache queue (if appropriate).