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vm pager: writemapping accounting for OBJT_SWAP

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Currently writemapping accounting is only done for vnode_pager which does
some accounting on the underlying vnode.

Extend this to allow accounting to be possible for any of the pager types.
New pageops are added to update/release writecount that need to be
implemented for any pager wishing to do said accounting, and we implement
these methods now for both vnode_pager (unchanged) and swap_pager.

The primary motivation for this is to allow other systems with OBJT_SWAP
objects to check if their objects have any write mappings and reject
operations with EBUSY if so. posixshm will be the first to do so in order to
reject adding write seals to the shmfd if any writable mappings exist.

Reviewed by:	kib, markj
Differential Revision:	https://reviews.freebsd.org/D21456
This commit is contained in:
Kyle Evans 2019-09-03 20:31:48 +00:00
parent ee6da5cee7
commit fe7bcbaf50
9 changed files with 90 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
sys/kern/vfs_vnops.c
View File

@ -87,7 +87,7 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vnode_pager.h>
#include <vm/vm_pager.h>
#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
@ -2502,7 +2502,7 @@ vn_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t size,
* writecount, then undo that now.
*/
if (writecounted)
vnode_pager_release_writecount(object, 0, size);
vm_pager_release_writecount(object, 0, size);
vm_object_deallocate(object);
}
#ifdef HWPMC_HOOKS

32
sys/vm/swap_pager.c
View File

@ -376,6 +376,10 @@ static boolean_t
static void swap_pager_init(void);
static void swap_pager_unswapped(vm_page_t);
static void swap_pager_swapoff(struct swdevt *sp);
static void swap_pager_update_writecount(vm_object_t object,
vm_offset_t start, vm_offset_t end);
static void swap_pager_release_writecount(vm_object_t object,
vm_offset_t start, vm_offset_t end);
struct pagerops swappagerops = {
.pgo_init = swap_pager_init, /* early system initialization of pager */
@ -386,6 +390,8 @@ struct pagerops swappagerops = {
.pgo_putpages = swap_pager_putpages, /* pageout */
.pgo_haspage = swap_pager_haspage, /* get backing store status for page */
.pgo_pageunswapped = swap_pager_unswapped, /* remove swap related to page */
.pgo_update_writecount = swap_pager_update_writecount,
.pgo_release_writecount = swap_pager_release_writecount,
};
/*
@ -611,6 +617,7 @@ swap_pager_alloc_init(void *handle, struct ucred *cred, vm_ooffset_t size,
object = vm_object_allocate(OBJT_SWAP, OFF_TO_IDX(offset +
PAGE_MASK + size));
object->un_pager.swp.writemappings = 0;
object->handle = handle;
if (cred != NULL) {
object->cred = cred;
@ -1903,6 +1910,7 @@ swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
atomic_thread_fence_rel();
object->type = OBJT_SWAP;
object->un_pager.swp.writemappings = 0;
KASSERT(object->handle == NULL, ("default pager with handle"));
}
@ -2991,3 +2999,27 @@ sysctl_swap_async_max(SYSCTL_HANDLER_ARGS)
return (0);
}
static void
swap_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
VM_OBJECT_WLOCK(object);
KASSERT((object->flags & OBJ_NOSPLIT) != 0,
("Splittable object with writecount"));
object->un_pager.swp.writemappings += (vm_ooffset_t)end - start;
VM_OBJECT_WUNLOCK(object);
}
static void
swap_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
VM_OBJECT_WLOCK(object);
KASSERT((object->flags & OBJ_NOSPLIT) != 0,
("Splittable object with writecount"));
object->un_pager.swp.writemappings -= (vm_ooffset_t)end - start;
VM_OBJECT_WUNLOCK(object);
}

34
sys/vm/vm_map.c
View File

@ -575,10 +575,10 @@ vm_map_process_deferred(void)
td->td_map_def_user = NULL;
while (entry != NULL) {
next = entry->next;
MPASS((entry->eflags & (MAP_ENTRY_VN_WRITECNT |
MAP_ENTRY_VN_EXEC)) != (MAP_ENTRY_VN_WRITECNT |
MPASS((entry->eflags & (MAP_ENTRY_WRITECNT |
MAP_ENTRY_VN_EXEC)) != (MAP_ENTRY_WRITECNT |
MAP_ENTRY_VN_EXEC));
if ((entry->eflags & MAP_ENTRY_VN_WRITECNT) != 0) {
if ((entry->eflags & MAP_ENTRY_WRITECNT) != 0) {
/*
* Decrement the object's writemappings and
* possibly the vnode's v_writecount.
@ -587,7 +587,7 @@ vm_map_process_deferred(void)
("Submap with writecount"));
object = entry->object.vm_object;
KASSERT(object != NULL, ("No object for writecount"));
vnode_pager_release_writecount(object, entry->start,
vm_pager_release_writecount(object, entry->start,
entry->end);
}
vm_map_entry_set_vnode_text(entry, false);
@ -1481,8 +1481,8 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
protoeflags |= MAP_ENTRY_GROWS_DOWN;
if (cow & MAP_STACK_GROWS_UP)
protoeflags |= MAP_ENTRY_GROWS_UP;
if (cow & MAP_VN_WRITECOUNT)
protoeflags |= MAP_ENTRY_VN_WRITECNT;
if (cow & MAP_WRITECOUNT)
protoeflags |= MAP_ENTRY_WRITECNT;
if (cow & MAP_VN_EXEC)
protoeflags |= MAP_ENTRY_VN_EXEC;
if ((cow & MAP_CREATE_GUARD) != 0)
@ -2211,7 +2211,7 @@ _vm_map_clip_start(vm_map_t map, vm_map_entry_t entry, vm_offset_t start)
vm_map_entry_set_vnode_text(new_entry, true);
/*
* The object->un_pager.vnp.writemappings for the
* object of MAP_ENTRY_VN_WRITECNT type entry shall be
* object of MAP_ENTRY_WRITECNT type entry shall be
* kept as is here. The virtual pages are
* re-distributed among the clipped entries, so the sum is
* left the same.
@ -3783,20 +3783,20 @@ vm_map_copy_entry(
dst_entry->eflags |= MAP_ENTRY_COW |
MAP_ENTRY_NEEDS_COPY;
dst_entry->offset = src_entry->offset;
if (src_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
if (src_entry->eflags & MAP_ENTRY_WRITECNT) {
/*
* MAP_ENTRY_VN_WRITECNT cannot
* MAP_ENTRY_WRITECNT cannot
* indicate write reference from
* src_entry, since the entry is
* marked as needs copy. Allocate a
* fake entry that is used to
* decrement object->un_pager.vnp.writecount
* decrement object->un_pager writecount
* at the appropriate time. Attach
* fake_entry to the deferred list.
*/
fake_entry = vm_map_entry_create(dst_map);
fake_entry->eflags = MAP_ENTRY_VN_WRITECNT;
src_entry->eflags &= ~MAP_ENTRY_VN_WRITECNT;
fake_entry->eflags = MAP_ENTRY_WRITECNT;
src_entry->eflags &= ~MAP_ENTRY_WRITECNT;
vm_object_reference(src_object);
fake_entry->object.vm_object = src_object;
fake_entry->start = src_entry->start;
@ -3971,7 +3971,7 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
* not relock it later for the assertion
* correctness.
*/
if (old_entry->eflags & MAP_ENTRY_VN_WRITECNT &&
if (old_entry->eflags & MAP_ENTRY_WRITECNT &&
object->type == OBJT_VNODE) {
KASSERT(((struct vnode *)object->handle)->
v_writecount > 0,
@ -3991,8 +3991,8 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
MAP_ENTRY_IN_TRANSITION);
new_entry->wiring_thread = NULL;
new_entry->wired_count = 0;
if (new_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
vnode_pager_update_writecount(object,
if (new_entry->eflags & MAP_ENTRY_WRITECNT) {
vm_pager_update_writecount(object,
new_entry->start, new_entry->end);
}
vm_map_entry_set_vnode_text(new_entry, true);
@ -4023,7 +4023,7 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
* Copied entry is COW over the old object.
*/
new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_VN_WRITECNT);
MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_WRITECNT);
new_entry->wiring_thread = NULL;
new_entry->wired_count = 0;
new_entry->object.vm_object = NULL;
@ -4047,7 +4047,7 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
new_entry->end = old_entry->end;
new_entry->eflags = old_entry->eflags &
~(MAP_ENTRY_USER_WIRED | MAP_ENTRY_IN_TRANSITION |
MAP_ENTRY_VN_WRITECNT | MAP_ENTRY_VN_EXEC);
MAP_ENTRY_WRITECNT | MAP_ENTRY_VN_EXEC);
new_entry->protection = old_entry->protection;
new_entry->max_protection = old_entry->max_protection;
new_entry->inheritance = VM_INHERIT_ZERO;

4
sys/vm/vm_map.h
View File

@ -144,7 +144,7 @@ struct vm_map_entry {
#define MAP_ENTRY_GROWS_UP 0x00002000 /* bottom-up stacks */
#define MAP_ENTRY_WIRE_SKIPPED 0x00004000
#define MAP_ENTRY_VN_WRITECNT 0x00008000 /* writeable vnode
#define MAP_ENTRY_WRITECNT 0x00008000 /* tracked writeable
mapping */
#define MAP_ENTRY_GUARD 0x00010000
#define MAP_ENTRY_STACK_GAP_DN 0x00020000
@ -348,7 +348,7 @@ long vmspace_resident_count(struct vmspace *vmspace);
#define MAP_CREATE_GUARD 0x00000080
#define MAP_DISABLE_COREDUMP 0x00000100
#define MAP_PREFAULT_MADVISE 0x00000200 /* from (user) madvise request */
#define MAP_VN_WRITECOUNT 0x00000400
#define MAP_WRITECOUNT 0x00000400
#define MAP_REMAP 0x00000800
#define MAP_STACK_GROWS_DOWN 0x00001000
#define MAP_STACK_GROWS_UP 0x00002000

8
sys/vm/vm_mmap.c
View File

@ -1289,7 +1289,7 @@ vm_mmap_vnode(struct thread *td, vm_size_t objsize,
}
if (writex) {
*writecounted = TRUE;
vnode_pager_update_writecount(obj, 0, objsize);
vm_pager_update_writecount(obj, 0, objsize);
}
} else {
error = EINVAL;
@ -1345,7 +1345,7 @@ vm_mmap_vnode(struct thread *td, vm_size_t objsize,
done:
if (error != 0 && *writecounted) {
*writecounted = FALSE;
vnode_pager_update_writecount(obj, objsize, 0);
vm_pager_update_writecount(obj, objsize, 0);
}
vput(vp);
return (error);
@ -1480,7 +1480,7 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
* writecount, then undo that now.
*/
if (writecounted)
vnode_pager_release_writecount(object, 0, size);
vm_pager_release_writecount(object, 0, size);
vm_object_deallocate(object);
}
return (error);
@ -1569,7 +1569,7 @@ vm_mmap_object(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
if (flags & MAP_SHARED)
docow |= MAP_INHERIT_SHARE;
if (writecounted)
docow |= MAP_VN_WRITECOUNT;
docow |= MAP_WRITECOUNT;
if (flags & MAP_STACK) {
if (object != NULL)
return (EINVAL);

1
sys/vm/vm_object.h
View File

@ -167,6 +167,7 @@ struct vm_object {
struct {
void *swp_tmpfs;
struct pctrie swp_blks;
vm_ooffset_t writemappings;
} swp;
} un_pager;
struct ucred *cred;

24
sys/vm/vm_pager.h
View File

@ -61,6 +61,7 @@ typedef boolean_t pgo_haspage_t(vm_object_t, vm_pindex_t, int *, int *);
typedef int pgo_populate_t(vm_object_t, vm_pindex_t, int, vm_prot_t,
vm_pindex_t *, vm_pindex_t *);
typedef void pgo_pageunswapped_t(vm_page_t);
typedef void pgo_writecount_t(vm_object_t, vm_offset_t, vm_offset_t);
struct pagerops {
pgo_init_t *pgo_init; /* Initialize pager. */
@ -72,6 +73,9 @@ struct pagerops {
pgo_haspage_t *pgo_haspage; /* Query page. */
pgo_populate_t *pgo_populate; /* Bulk spec pagein. */
pgo_pageunswapped_t *pgo_pageunswapped;
/* Operations for specialized writecount handling */
pgo_writecount_t *pgo_update_writecount;
pgo_writecount_t *pgo_release_writecount;
};
extern struct pagerops defaultpagerops;
@ -192,6 +196,26 @@ vm_pager_page_unswapped(vm_page_t m)
(*pagertab[m->object->type]->pgo_pageunswapped)(m);
}
static __inline void
vm_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
if (pagertab[object->type]->pgo_update_writecount)
pagertab[object->type]->pgo_update_writecount(object, start,
end);
}
static __inline void
vm_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
if (pagertab[object->type]->pgo_release_writecount)
pagertab[object->type]->pgo_release_writecount(object, start,
end);
}
struct cdev_pager_ops {
int (*cdev_pg_fault)(vm_object_t vm_obj, vm_ooffset_t offset,
int prot, vm_page_t *mres);

10
sys/vm/vnode_pager.c
View File

@ -100,6 +100,10 @@ static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
vm_ooffset_t, struct ucred *cred);
static int vnode_pager_generic_getpages_done(struct buf *);
static void vnode_pager_generic_getpages_done_async(struct buf *);
static void vnode_pager_update_writecount(vm_object_t, vm_offset_t,
vm_offset_t);
static void vnode_pager_release_writecount(vm_object_t, vm_offset_t,
vm_offset_t);
struct pagerops vnodepagerops = {
.pgo_alloc = vnode_pager_alloc,
@ -108,6 +112,8 @@ struct pagerops vnodepagerops = {
.pgo_getpages_async = vnode_pager_getpages_async,
.pgo_putpages = vnode_pager_putpages,
.pgo_haspage = vnode_pager_haspage,
.pgo_update_writecount = vnode_pager_update_writecount,
.pgo_release_writecount = vnode_pager_release_writecount,
};
static struct domainset *vnode_domainset = NULL;
@ -1500,7 +1506,7 @@ vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written, off_t eof,
VM_OBJECT_WUNLOCK(obj);
}
void
static void
vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
@ -1529,7 +1535,7 @@ vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
VM_OBJECT_WUNLOCK(object);
}
void
static void
vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{

4
sys/vm/vnode_pager.h
View File

@ -50,12 +50,8 @@ int vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *m,
int vnode_pager_local_getpages(struct vop_getpages_args *ap);
int vnode_pager_local_getpages_async(struct vop_getpages_async_args *ap);
int vnode_pager_putpages_ioflags(int pager_flags);
void vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end);
void vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written,
off_t eof, int lpos);
void vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end);
#endif /* _KERNEL */
#endif /* _VNODE_PAGER_ */