d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Add unlocked grab* function variants that use lockless radix code to

Browse Source 
lookup pages.  These variants will fall back to their locked counterparts
if the page is not present.

Discussed with:	kib, markj
Differential Revision:	https://reviews.freebsd.org/D23449
This commit is contained in:
Jeff Roberson 2020-02-27 02:37:27 +00:00
parent 600ee699ed
commit c49be4f1c6
2 changed files with 341 additions and 95 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

427
sys/vm/vm_page.c
View File

@ -830,47 +830,39 @@ vm_page_reference(vm_page_t m)
vm_page_aflag_set(m, PGA_REFERENCED);
}
/*
* vm_page_trybusy
*
* Helper routine for grab functions to trylock busy.
*
* Returns true on success and false on failure.
*/
static bool
vm_page_acquire_flags(vm_page_t m, int allocflags)
vm_page_trybusy(vm_page_t m, int allocflags)
{
bool locked;
if ((allocflags & (VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY)) != 0)
locked = vm_page_trysbusy(m);
return (vm_page_trysbusy(m));
else
locked = vm_page_tryxbusy(m);
if (locked && (allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
return (locked);
return (vm_page_tryxbusy(m));
}
/*
* vm_page_busy_sleep_flags
* vm_page_tryacquire
*
* Sleep for busy according to VM_ALLOC_ parameters. Returns true
* if the caller should retry and false otherwise.
* Helper routine for grab functions to trylock busy and wire.
*
* Returns true on success and false on failure.
*/
static bool
vm_page_busy_sleep_flags(vm_object_t object, vm_page_t m, const char *wmesg,
int allocflags)
static inline bool
vm_page_tryacquire(vm_page_t m, int allocflags)
{
bool locked;
if ((allocflags & VM_ALLOC_NOWAIT) != 0)
return (false);
/*
* Reference the page before unlocking and sleeping so that
* the page daemon is less likely to reclaim it.
*/
if ((allocflags & VM_ALLOC_NOCREAT) == 0)
vm_page_reference(m);
if (_vm_page_busy_sleep(object, m, m->pindex, wmesg, allocflags, true))
VM_OBJECT_WLOCK(object);
if ((allocflags & VM_ALLOC_WAITFAIL) != 0)
return (false);
return (true);
locked = vm_page_trybusy(m, allocflags);
if (locked && (allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
return (locked);
}
/*
@ -894,7 +886,7 @@ vm_page_busy_acquire(vm_page_t m, int allocflags)
*/
obj = m->object;
for (;;) {
if (vm_page_acquire_flags(m, allocflags))
if (vm_page_tryacquire(m, allocflags))
return (true);
if ((allocflags & VM_ALLOC_NOWAIT) != 0)
return (false);
@ -1604,6 +1596,7 @@ vm_page_object_remove(vm_page_t m)
if ((m->a.flags & PGA_SWAP_FREE) != 0)
vm_pager_page_unswapped(m);
m->object = NULL;
mrem = vm_radix_remove(&object->rtree, m->pindex);
KASSERT(mrem == m, ("removed page %p, expected page %p", mrem, m));
@ -1658,7 +1651,6 @@ vm_page_remove_xbusy(vm_page_t m)
{
vm_page_object_remove(m);
m->object = NULL;
return (vm_page_drop(m, VPRC_OBJREF) == VPRC_OBJREF);
}
@ -1678,6 +1670,38 @@ vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
return (vm_radix_lookup(&object->rtree, pindex));
}
/*
* This should only be used by lockless functions for releasing transient
* incorrect acquires. The page may have been freed after we acquired a
* busy lock. In this case busy_lock == VPB_FREED and we have nothing
* further to do.
*/
static void
vm_page_busy_release(vm_page_t m)
{
u_int x;
x = atomic_load_int(&m->busy_lock);
for (;;) {
if (x == VPB_FREED)
break;
if ((x & VPB_BIT_SHARED) != 0 && VPB_SHARERS(x) > 1) {
if (atomic_fcmpset_int(&m->busy_lock, &x,
x - VPB_ONE_SHARER))
break;
continue;
}
KASSERT((x & VPB_BIT_SHARED) != 0 ||
(x & ~VPB_BIT_WAITERS) == VPB_CURTHREAD_EXCLUSIVE,
("vm_page_busy_release: %p xbusy not owned.", m));
if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED))
continue;
if ((x & VPB_BIT_WAITERS) != 0)
wakeup(m);
break;
}
}
/*
* vm_page_find_least:
*
@ -3688,7 +3712,6 @@ vm_page_free_prep(vm_page_t m)
("vm_page_free_prep: page %p has unexpected ref_count %u",
m, m->ref_count));
vm_page_object_remove(m);
m->object = NULL;
m->ref_count -= VPRC_OBJREF;
} else
vm_page_assert_unbusied(m);
@ -4245,18 +4268,81 @@ vm_page_advise(vm_page_t m, int advice)
vm_page_launder(m);
}
/*
* vm_page_grab_release
*
* Helper routine for grab functions to release busy on return.
*/
static inline void
vm_page_grab_release(vm_page_t m, int allocflags)
{
if ((allocflags & VM_ALLOC_NOBUSY) != 0) {
if ((allocflags & VM_ALLOC_IGN_SBUSY) != 0)
vm_page_sunbusy(m);
else
vm_page_xunbusy(m);
}
}
/*
* vm_page_grab_sleep
*
* Sleep for busy according to VM_ALLOC_ parameters. Returns true
* if the caller should retry and false otherwise.
*
* If the object is locked on entry the object will be unlocked with
* false returns and still locked but possibly having been dropped
* with true returns.
*/
static bool
vm_page_grab_sleep(vm_object_t object, vm_page_t m, vm_pindex_t pindex,
const char *wmesg, int allocflags, bool locked)
{
if ((allocflags & VM_ALLOC_NOWAIT) != 0)
return (false);
/*
* Reference the page before unlocking and sleeping so that
* the page daemon is less likely to reclaim it.
*/
if (locked && (allocflags & VM_ALLOC_NOCREAT) == 0)
vm_page_reference(m);
if (_vm_page_busy_sleep(object, m, m->pindex, wmesg, allocflags,
locked) && locked)
VM_OBJECT_WLOCK(object);
if ((allocflags & VM_ALLOC_WAITFAIL) != 0)
return (false);
return (true);
}
/*
* Assert that the grab flags are valid.
*/
static inline void
vm_page_grab_check(int allocflags)
{
KASSERT((allocflags & VM_ALLOC_NOBUSY) == 0 ||
(allocflags & VM_ALLOC_WIRED) != 0,
("vm_page_grab*: the pages must be busied or wired"));
KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
(allocflags & VM_ALLOC_IGN_SBUSY) != 0,
("vm_page_grab*: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY mismatch"));
}
/*
* Calculate the page allocation flags for grab.
*/
static inline int
vm_page_grab_pflags(int allocflags)
{
int pflags;
KASSERT((allocflags & VM_ALLOC_NOBUSY) == 0 ||
(allocflags & VM_ALLOC_WIRED) != 0,
("vm_page_grab_pflags: the pages must be busied or wired"));
KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
(allocflags & VM_ALLOC_IGN_SBUSY) != 0,
("vm_page_grab_pflags: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY "
"mismatch"));
pflags = allocflags &
~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL |
VM_ALLOC_NOBUSY);
@ -4283,15 +4369,15 @@ vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
vm_page_t m;
int pflags;
VM_OBJECT_ASSERT_WLOCKED(object);
pflags = vm_page_grab_pflags(allocflags);
vm_page_grab_check(allocflags);
retrylookup:
if ((m = vm_page_lookup(object, pindex)) != NULL) {
if (!vm_page_acquire_flags(m, allocflags)) {
if (vm_page_busy_sleep_flags(object, m, "pgrbwt",
allocflags))
if (!vm_page_tryacquire(m, allocflags)) {
if (vm_page_grab_sleep(object, m, pindex, "pgrbwt",
allocflags, true))
goto retrylookup;
return (NULL);
}
@ -4299,7 +4385,7 @@ vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
}
if ((allocflags & VM_ALLOC_NOCREAT) != 0)
return (NULL);
m = vm_page_alloc(object, pindex, pflags);
m = vm_page_alloc(object, pindex, vm_page_grab_pflags(allocflags));
if (m == NULL) {
if ((allocflags & (VM_ALLOC_NOWAIT | VM_ALLOC_WAITFAIL)) != 0)
return (NULL);
@ -4309,12 +4395,104 @@ vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
pmap_zero_page(m);
out:
if ((allocflags & VM_ALLOC_NOBUSY) != 0) {
if ((allocflags & VM_ALLOC_IGN_SBUSY) != 0)
vm_page_sunbusy(m);
else
vm_page_xunbusy(m);
vm_page_grab_release(m, allocflags);
return (m);
}
/*
* Locklessly attempt to acquire a page given a (object, pindex) tuple
* and an optional previous page to avoid the radix lookup. The resulting
* page will be validated against the identity tuple and busied or wired
* as requested. A NULL *mp return guarantees that the page was not in
* radix at the time of the call but callers must perform higher level
* synchronization or retry the operation under a lock if they require
* an atomic answer. This is the only lock free validation routine,
* other routines can depend on the resulting page state.
*
* The return value indicates whether the operation failed due to caller
* flags. The return is tri-state with mp:
*
* (true, *mp != NULL) - The operation was successful.
* (true, *mp == NULL) - The page was not found in tree.
* (false, *mp == NULL) - WAITFAIL or NOWAIT prevented acquisition.
*/
static bool
vm_page_acquire_unlocked(vm_object_t object, vm_pindex_t pindex,
vm_page_t prev, vm_page_t *mp, int allocflags)
{
vm_page_t m;
vm_page_grab_check(allocflags);
MPASS(prev == NULL || vm_page_busied(prev) || vm_page_wired(prev));
*mp = NULL;
for (;;) {
/*
* We may see a false NULL here because the previous page
* has been removed or just inserted and the list is loaded
* without barriers. Switch to radix to verify.
*/
if (prev == NULL || (m = TAILQ_NEXT(prev, listq)) == NULL ||
m->pindex != pindex ||
atomic_load_ptr(&m->object) != object) {
prev = NULL;
/*
* This guarantees the result is instantaneously
* correct.
*/
m = vm_radix_lookup_unlocked(&object->rtree, pindex);
}
if (m == NULL)
return (true);
if (vm_page_trybusy(m, allocflags)) {
if (m->object == object && m->pindex == pindex)
break;
/* relookup. */
vm_page_busy_release(m);
cpu_spinwait();
continue;
}
if (!vm_page_grab_sleep(object, m, pindex, "pgnslp",
allocflags, false))
return (false);
}
if ((allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
vm_page_grab_release(m, allocflags);
*mp = m;
return (true);
}
/*
* Try to locklessly grab a page and fall back to the object lock if NOCREAT
* is not set.
*/
vm_page_t
vm_page_grab_unlocked(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
vm_page_t m;
vm_page_grab_check(allocflags);
if (!vm_page_acquire_unlocked(object, pindex, NULL, &m, allocflags))
return (NULL);
if (m != NULL)
return (m);
/*
* The radix lockless lookup should never return a false negative
* errors. If the user specifies NOCREAT they are guaranteed there
* was no page present at the instant of the call. A NOCREAT caller
* must handle create races gracefully.
*/
if ((allocflags & VM_ALLOC_NOCREAT) != 0)
return (NULL);
VM_OBJECT_WLOCK(object);
m = vm_page_grab(object, pindex, allocflags);
VM_OBJECT_WUNLOCK(object);
return (m);
}
@ -4330,7 +4508,6 @@ vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int al
{
vm_page_t m;
vm_page_t ma[VM_INITIAL_PAGEIN];
bool sleep, xbusy;
int after, i, pflags, rv;
KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
@ -4344,7 +4521,6 @@ vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int al
pflags |= VM_ALLOC_WAITFAIL;
retrylookup:
xbusy = false;
if ((m = vm_page_lookup(object, pindex)) != NULL) {
/*
* If the page is fully valid it can only become invalid
@ -4355,41 +4531,27 @@ vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int al
* However, we will not end up with an invalid page and a
* shared lock.
*/
if (!vm_page_all_valid(m) ||
(allocflags & (VM_ALLOC_IGN_SBUSY | VM_ALLOC_SBUSY)) == 0) {
sleep = !vm_page_tryxbusy(m);
xbusy = true;
} else
sleep = !vm_page_trysbusy(m);
if (sleep) {
(void)vm_page_busy_sleep_flags(object, m, "pgrbwt",
allocflags);
if (!vm_page_trybusy(m,
vm_page_all_valid(m) ? allocflags : 0)) {
(void)vm_page_grab_sleep(object, m, pindex, "pgrbwt",
allocflags, true);
goto retrylookup;
}
if ((allocflags & VM_ALLOC_NOCREAT) != 0 &&
!vm_page_all_valid(m)) {
if (xbusy)
vm_page_xunbusy(m);
else
vm_page_sunbusy(m);
if (vm_page_all_valid(m))
goto out;
if ((allocflags & VM_ALLOC_NOCREAT) != 0) {
vm_page_busy_release(m);
*mp = NULL;
return (VM_PAGER_FAIL);
}
if ((allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
if (vm_page_all_valid(m))
goto out;
} else if ((allocflags & VM_ALLOC_NOCREAT) != 0) {
*mp = NULL;
return (VM_PAGER_FAIL);
} else if ((m = vm_page_alloc(object, pindex, pflags)) != NULL) {
xbusy = true;
} else {
} else if ((m = vm_page_alloc(object, pindex, pflags)) == NULL) {
goto retrylookup;
}
vm_page_assert_xbusied(m);
MPASS(xbusy);
if (vm_pager_has_page(object, pindex, NULL, &after)) {
after = MIN(after, VM_INITIAL_PAGEIN);
after = MIN(after, allocflags >> VM_ALLOC_COUNT_SHIFT);
@ -4415,8 +4577,6 @@ vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int al
/* Pager may have replaced a page. */
m = ma[0];
if (rv != VM_PAGER_OK) {
if ((allocflags & VM_ALLOC_WIRED) != 0)
vm_page_unwire_noq(m);
for (i = 0; i < after; i++) {
if (!vm_page_wired(ma[i]))
vm_page_free(ma[i]);
@ -4433,18 +4593,59 @@ vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex, int al
vm_page_zero_invalid(m, TRUE);
}
out:
if ((allocflags & VM_ALLOC_NOBUSY) != 0) {
if (xbusy)
vm_page_xunbusy(m);
else
vm_page_sunbusy(m);
}
if ((allocflags & VM_ALLOC_SBUSY) != 0 && xbusy)
if ((allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
if ((allocflags & VM_ALLOC_SBUSY) != 0 && vm_page_xbusied(m))
vm_page_busy_downgrade(m);
else if ((allocflags & VM_ALLOC_NOBUSY) != 0)
vm_page_busy_release(m);
*mp = m;
return (VM_PAGER_OK);
}
/*
* Locklessly grab a valid page. If the page is not valid or not yet
* allocated this will fall back to the object lock method.
*/
int
vm_page_grab_valid_unlocked(vm_page_t *mp, vm_object_t object,
vm_pindex_t pindex, int allocflags)
{
vm_page_t m;
int flags;
int error;
KASSERT((allocflags & VM_ALLOC_SBUSY) == 0 ||
(allocflags & VM_ALLOC_IGN_SBUSY) != 0,
("vm_page_grab_valid_unlocked: VM_ALLOC_SBUSY/VM_ALLOC_IGN_SBUSY "
"mismatch"));
KASSERT((allocflags &
(VM_ALLOC_NOWAIT | VM_ALLOC_WAITFAIL | VM_ALLOC_ZERO)) == 0,
("vm_page_grab_valid_unlocked: Invalid flags 0x%X", allocflags));
/*
* Attempt a lockless lookup and busy. We need at least an sbusy
* before we can inspect the valid field and return a wired page.
*/
flags = allocflags & ~(VM_ALLOC_NOBUSY | VM_ALLOC_WIRED);
if (!vm_page_acquire_unlocked(object, pindex, NULL, mp, flags))
return (VM_PAGER_FAIL);
if ((m = *mp) != NULL) {
if (vm_page_all_valid(m)) {
if ((allocflags & VM_ALLOC_WIRED) != 0)
vm_page_wire(m);
vm_page_grab_release(m, allocflags);
return (VM_PAGER_OK);
}
vm_page_busy_release(m);
}
VM_OBJECT_WLOCK(object);
error = vm_page_grab_valid(mp, object, pindex, allocflags);
VM_OBJECT_WUNLOCK(object);
return (error);
}
/*
* Return the specified range of pages from the given object. For each
* page offset within the range, if a page already exists within the object
@ -4482,6 +4683,7 @@ vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
VM_OBJECT_ASSERT_WLOCKED(object);
KASSERT(((u_int)allocflags >> VM_ALLOC_COUNT_SHIFT) == 0,
("vm_page_grap_pages: VM_ALLOC_COUNT() is not allowed"));
vm_page_grab_check(allocflags);
pflags = vm_page_grab_pflags(allocflags);
if (count == 0)
@ -4497,9 +4699,9 @@ vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
mpred = TAILQ_PREV(m, pglist, listq);
for (; i < count; i++) {
if (m != NULL) {
if (!vm_page_acquire_flags(m, allocflags)) {
if (vm_page_busy_sleep_flags(object, m,
"grbmaw", allocflags))
if (!vm_page_tryacquire(m, allocflags)) {
if (vm_page_grab_sleep(object, m, pindex,
"grbmaw", allocflags, true))
goto retrylookup;
break;
}
@ -4521,18 +4723,57 @@ vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
pmap_zero_page(m);
vm_page_valid(m);
}
if ((allocflags & VM_ALLOC_NOBUSY) != 0) {
if ((allocflags & VM_ALLOC_IGN_SBUSY) != 0)
vm_page_sunbusy(m);
else
vm_page_xunbusy(m);
}
vm_page_grab_release(m, allocflags);
ma[i] = mpred = m;
m = vm_page_next(m);
}
return (i);
}
/*
* Unlocked variant of vm_page_grab_pages(). This accepts the same flags
* and will fall back to the locked variant to handle allocation.
*/
int
vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
int allocflags, vm_page_t *ma, int count)
{
vm_page_t m, pred;
int flags;
int i;
vm_page_grab_check(allocflags);
/*
* Modify flags for lockless acquire to hold the page until we
* set it valid if necessary.
*/
flags = allocflags & ~VM_ALLOC_NOBUSY;
pred = NULL;
for (i = 0; i < count; i++, pindex++) {
if (!vm_page_acquire_unlocked(object, pindex, pred, &m, flags))
return (i);
if (m == NULL)
break;
if ((flags & VM_ALLOC_ZERO) != 0 && vm_page_none_valid(m)) {
if ((m->flags & PG_ZERO) == 0)
pmap_zero_page(m);
vm_page_valid(m);
}
/* m will still be wired or busy according to flags. */
vm_page_grab_release(m, allocflags);
pred = ma[i] = m;
}
if ((allocflags & VM_ALLOC_NOCREAT) != 0)
return (i);
count -= i;
VM_OBJECT_WLOCK(object);
i += vm_page_grab_pages(object, pindex, allocflags, &ma[i], count);
VM_OBJECT_WUNLOCK(object);
return (i);
}
/*
* Mapping function for valid or dirty bits in a page.
*

5
sys/vm/vm_page.h
View File

@ -615,10 +615,15 @@ vm_page_t vm_page_alloc_freelist_domain(int, int, int);
void vm_page_bits_set(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t set);
bool vm_page_blacklist_add(vm_paddr_t pa, bool verbose);
vm_page_t vm_page_grab(vm_object_t, vm_pindex_t, int);
vm_page_t vm_page_grab_unlocked(vm_object_t, vm_pindex_t, int);
int vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
vm_page_t *ma, int count);
int vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
int allocflags, vm_page_t *ma, int count);
int vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex,
int allocflags);
int vm_page_grab_valid_unlocked(vm_page_t *mp, vm_object_t object,
vm_pindex_t pindex, int allocflags);
void vm_page_deactivate(vm_page_t);
void vm_page_deactivate_noreuse(vm_page_t);
void vm_page_dequeue(vm_page_t m);