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vm_object: Modify vm_object_allocate_anon() to return OBJT_SWAP objects

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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
This commit is contained in:
Mark Johnston 2022-07-16 11:27:27 -04:00
parent 6226f8f254
commit 5d32157d4e
3 changed files with 27 additions and 9 deletions
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25
sys/vm/vm_fault.c
View file

@ -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"));

8
sys/vm/vm_object.c
View file

@ -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);

3
sys/vm/vm_object.h
View file

@ -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 */