git: 5d32157d4e5c - main - vm_object: Modify vm_object_allocate_anon() to return OBJT_SWAP objects

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=5d32157d4e5c2dfda5ca39d40bf4620b04fc2b29

commit 5d32157d4e5c2dfda5ca39d40bf4620b04fc2b29
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2022-07-16 15:27:27 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2022-07-17 11:09:48 +0000

    vm_object: Modify vm_object_allocate_anon() to return OBJT_SWAP objects
    
    With this change, OBJT_DEFAULT objects are no longer allocated.
    Instead, anonymous objects are always of type OBJT_SWAP and always have
    OBJ_SWAP set.
    
    Modify the page fault handler to check the swap block radix tree in
    places where it checked for objects of type OBJT_DEFAULT.  In
    particular, there's no need to invoke getpages for an OBJT_SWAP object
    with no swap blocks assigned.
    
    Reviewed by:    alc, kib
    Tested by:      pho
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D35785
---
 sys/vm/vm_fault.c  | 25 ++++++++++++++++++++-----
 sys/vm/vm_object.c |  8 +++++---
 sys/vm/vm_object.h |  3 ++-
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index c379301f866f..d398be941e84 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -85,6 +85,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/lock.h>
 #include <sys/mman.h>
 #include <sys/mutex.h>
+#include <sys/pctrie.h>
 #include <sys/proc.h>
 #include <sys/racct.h>
 #include <sys/refcount.h>
@@ -220,6 +221,21 @@ fault_page_free(vm_page_t *mp)
 	}
 }
 
+/*
+ * Return true if a vm_pager_get_pages() call is needed in order to check
+ * whether the pager might have a particular page, false if it can be determined
+ * immediately that the pager can not have a copy.  For swap objects, this can
+ * be checked quickly.
+ */
+static inline bool
+fault_object_needs_getpages(vm_object_t object)
+{
+	VM_OBJECT_ASSERT_LOCKED(object);
+
+	return ((object->flags & OBJ_SWAP) == 0 ||
+	    !pctrie_is_empty(&object->un_pager.swp.swp_blks));
+}
+
 static inline void
 unlock_map(struct faultstate *fs)
 {
@@ -1406,10 +1422,9 @@ vm_fault_object(struct faultstate *fs, int *behindp, int *aheadp)
 	/*
 	 * Page is not resident.  If the pager might contain the page
 	 * or this is the beginning of the search, allocate a new
-	 * page.  (Default objects are zero-fill, so there is no real
-	 * pager for them.)
+	 * page.
 	 */
-	if (fs->m == NULL && (fs->object->type != OBJT_DEFAULT ||
+	if (fs->m == NULL && (fault_object_needs_getpages(fs->object) ||
 	    fs->object == fs->first_object)) {
 		res = vm_fault_allocate(fs);
 		if (res != FAULT_CONTINUE)
@@ -1422,7 +1437,7 @@ vm_fault_object(struct faultstate *fs, int *behindp, int *aheadp)
 	 * object without dropping the lock to preserve atomicity of
 	 * shadow faults.
 	 */
-	if (fs->object->type != OBJT_DEFAULT) {
+	if (fault_object_needs_getpages(fs->object)) {
 		/*
 		 * At this point, we have either allocated a new page
 		 * or found an existing page that is only partially
@@ -1841,7 +1856,7 @@ vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
 		if (!obj_locked)
 			VM_OBJECT_RLOCK(lobject);
 		while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
-		    lobject->type == OBJT_DEFAULT &&
+		    !fault_object_needs_getpages(lobject) &&
 		    (backing_object = lobject->backing_object) != NULL) {
 			KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
 			    0, ("vm_fault_prefault: unaligned object offset"));
diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index 4272a734b233..57904454eff7 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -244,8 +244,10 @@ _vm_object_allocate(objtype_t type, vm_pindex_t size, u_short flags,
 
 	object->type = type;
 	object->flags = flags;
-	if ((flags & OBJ_SWAP) != 0)
+	if ((flags & OBJ_SWAP) != 0) {
 		pctrie_init(&object->un_pager.swp.swp_blks);
+		object->un_pager.swp.writemappings = 0;
+	}
 
 	/*
 	 * Ensure that swap_pager_swapoff() iteration over object_list
@@ -473,8 +475,8 @@ vm_object_allocate_anon(vm_pindex_t size, vm_object_t backing_object,
 	else
 		handle = backing_object;
 	object = uma_zalloc(obj_zone, M_WAITOK);
-	_vm_object_allocate(OBJT_DEFAULT, size, OBJ_ANON | OBJ_ONEMAPPING,
-	    object, handle);
+	_vm_object_allocate(OBJT_SWAP, size,
+	    OBJ_ANON | OBJ_ONEMAPPING | OBJ_SWAP, object, handle);
 	object->cred = cred;
 	object->charge = cred != NULL ? charge : 0;
 	return (object);
diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
index 80e84dcabf98..719198637726 100644
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -202,7 +202,8 @@ struct vm_object {
 #define	OBJ_SIZEVNLOCK	0x0040		/* lock vnode to check obj size */
 #define	OBJ_PG_DTOR	0x0080		/* dont reset object, leave that for dtor */
 #define	OBJ_SHADOWLIST	0x0100		/* Object is on the shadow list. */
-#define	OBJ_SWAP	0x0200		/* object swaps */
+#define	OBJ_SWAP	0x0200		/* object swaps, type will be OBJT_SWAP
+					   or dynamically registered */
 #define	OBJ_SPLIT	0x0400		/* object is being split */
 #define	OBJ_COLLAPSING	0x0800		/* Parent of collapse. */
 #define	OBJ_COLORED	0x1000		/* pg_color is defined */