(1/6) Replace busy checks with acquires where it is trival to do so.

This is the first in a series of patches that promotes the page busy field
to a first class lock that no longer requires the object lock for
consistency.

Reviewed by:	kib, markj
Tested by:	pho
Sponsored by:	Netflix, Intel
Differential Revision:	https://reviews.freebsd.org/D21548

1 files changed, 23 insertions, 25 deletions

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 8e14592b402d..baeaf2e32dc0 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -2945,10 +2945,10 @@ vfs_vmio_invalidate(struct buf *bp)
 		presid = resid > (PAGE_SIZE - poffset) ?
 		    (PAGE_SIZE - poffset) : resid;
 		KASSERT(presid >= 0, ("brelse: extra page"));
-		while (vm_page_xbusied(m))
-			vm_page_sleep_if_xbusy(m, "mbncsh");
+		vm_page_busy_acquire(m, VM_ALLOC_SBUSY);
 		if (pmap_page_wired_mappings(m) == 0)
 			vm_page_set_invalid(m, poffset, presid);
+		vm_page_sunbusy(m);
 		vm_page_release_locked(m, flags);
 		resid -= presid;
 		poffset = 0;
@@ -3651,7 +3651,7 @@ vfs_clean_pages_dirty_buf(struct buf *bp)
 	    ("vfs_clean_pages_dirty_buf: no buffer offset"));
 
 	VM_OBJECT_WLOCK(bp->b_bufobj->bo_object);
-	vfs_drain_busy_pages(bp);
+	vfs_busy_pages_acquire(bp);
 	vfs_setdirty_locked_object(bp);
 	for (i = 0; i < bp->b_npages; i++) {
 		noff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
@@ -3663,6 +3663,7 @@ vfs_clean_pages_dirty_buf(struct buf *bp)
 		/* vm_page_clear_dirty(m, foff & PAGE_MASK, eoff - foff); */
 		foff = noff;
 	}
+	vfs_busy_pages_release(bp);
 	VM_OBJECT_WUNLOCK(bp->b_bufobj->bo_object);
 }
 
@@ -4559,28 +4560,25 @@ vfs_page_set_validclean(struct buf *bp, vm_ooffset_t off, vm_page_t m)
 }
 
 /*
- * Ensure that all buffer pages are not exclusive busied.  If any page is
- * exclusive busy, drain it.
+ * Acquire a shared busy on all pages in the buf.
  */
 void
-vfs_drain_busy_pages(struct buf *bp)
+vfs_busy_pages_acquire(struct buf *bp)
 {
-	vm_page_t m;
-	int i, last_busied;
+	int i;
 
 	VM_OBJECT_ASSERT_WLOCKED(bp->b_bufobj->bo_object);
-	last_busied = 0;
-	for (i = 0; i < bp->b_npages; i++) {
-		m = bp->b_pages[i];
-		if (vm_page_xbusied(m)) {
-			for (; last_busied < i; last_busied++)
-				vm_page_sbusy(bp->b_pages[last_busied]);
-			while (vm_page_xbusied(m)) {
-				vm_page_sleep_if_xbusy(m, "vbpage");
-			}
-		}
-	}
-	for (i = 0; i < last_busied; i++)
+	for (i = 0; i < bp->b_npages; i++)
+		vm_page_busy_acquire(bp->b_pages[i], VM_ALLOC_SBUSY);
+}
+
+void
+vfs_busy_pages_release(struct buf *bp)
+{
+	int i;
+
+	VM_OBJECT_ASSERT_WLOCKED(bp->b_bufobj->bo_object);
+	for (i = 0; i < bp->b_npages; i++)
 		vm_page_sunbusy(bp->b_pages[i]);
 }
 
@@ -4613,17 +4611,17 @@ vfs_busy_pages(struct buf *bp, int clear_modify)
 	KASSERT(bp->b_offset != NOOFFSET,
 	    ("vfs_busy_pages: no buffer offset"));
 	VM_OBJECT_WLOCK(obj);
-	vfs_drain_busy_pages(bp);
+	if ((bp->b_flags & B_CLUSTER) == 0) {
+		vm_object_pip_add(obj, bp->b_npages);
+		vfs_busy_pages_acquire(bp);
+	}
 	if (bp->b_bufsize != 0)
 		vfs_setdirty_locked_object(bp);
 	bogus = false;
 	for (i = 0; i < bp->b_npages; i++) {
 		m = bp->b_pages[i];
+		vm_page_assert_sbusied(m);
 
-		if ((bp->b_flags & B_CLUSTER) == 0) {
-			vm_object_pip_add(obj, 1);
-			vm_page_sbusy(m);
-		}
 		/*
 		 * When readying a buffer for a read ( i.e
 		 * clear_modify == 0 ), it is important to do