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Reduce the code size and number of ffsl calls in vm_reserv_break. Use

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xor to find where free ranges begin and end.

Tested by: pho
Reviewed by:alc
Approved by:markj, kib (mentors)
Differential Revision:	https://reviews.freebsd.org/D20256
This commit is contained in:
Doug Moore 2019-05-28 00:51:23 +00:00
parent 2b3899c0ee
commit e67a5068ec
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=348318
1 changed files with 34 additions and 41 deletions
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75
sys/vm/vm_reserv.c
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@ -1030,56 +1030,49 @@ vm_reserv_alloc_page(int req, vm_object_t object, vm_pindex_t pindex, int domain
static void
vm_reserv_break(vm_reserv_t rv)
{
int begin_zeroes, hi, i, lo;
u_long changes;
int bitpos, hi, i, lo;
vm_reserv_assert_locked(rv);
CTR5(KTR_VM, "%s: rv %p object %p popcnt %d inpartpop %d",
__FUNCTION__, rv, rv->object, rv->popcnt, rv->inpartpopq);
vm_reserv_remove(rv);
rv->pages->psind = 0;
i = hi = 0;
do {
/* Find the next 0 bit. Any previous 0 bits are < "hi". */
lo = ffsl(~(((1UL << hi) - 1) | rv->popmap[i]));
if (lo == 0) {
/* Redundantly clears bits < "hi". */
hi = lo = -1;
for (i = 0; i <= NPOPMAP; i++) {
/*
* "changes" is a bitmask that marks where a new sequence of
* 0s or 1s begins in popmap[i], with last bit in popmap[i-1]
* considered to be 1 if and only if lo == hi. The bits of
* popmap[-1] and popmap[NPOPMAP] are considered all 1s.
*/
if (i == NPOPMAP)
changes = lo != hi;
else {
changes = rv->popmap[i];
changes ^= (changes << 1) | (lo == hi);
rv->popmap[i] = 0;
rv->popcnt -= NBPOPMAP - hi;
while (++i < NPOPMAP) {
lo = ffsl(~rv->popmap[i]);
if (lo == 0) {
rv->popmap[i] = 0;
rv->popcnt -= NBPOPMAP;
} else
break;
}
while (changes != 0) {
/*
* If the next change marked begins a run of 0s, set
* lo to mark that position. Otherwise set hi and
* free pages from lo up to hi.
*/
bitpos = ffsl(changes) - 1;
changes ^= 1UL << bitpos;
if (lo == hi)
lo = NBPOPMAP * i + bitpos;
else {
hi = NBPOPMAP * i + bitpos;
vm_domain_free_lock(VM_DOMAIN(rv->domain));
vm_phys_free_contig(&rv->pages[lo], hi - lo);
vm_domain_free_unlock(VM_DOMAIN(rv->domain));
lo = hi;
}
if (i == NPOPMAP)
break;
hi = 0;
}
KASSERT(lo > 0, ("vm_reserv_break: lo is %d", lo));
/* Convert from ffsl() to ordinary bit numbering. */
lo--;
if (lo > 0) {
/* Redundantly clears bits < "hi". */
rv->popmap[i] &= ~((1UL << lo) - 1);
rv->popcnt -= lo - hi;
}
begin_zeroes = NBPOPMAP * i + lo;
/* Find the next 1 bit. */
do
hi = ffsl(rv->popmap[i]);
while (hi == 0 && ++i < NPOPMAP);
if (i != NPOPMAP)
/* Convert from ffsl() to ordinary bit numbering. */
hi--;
vm_domain_free_lock(VM_DOMAIN(rv->domain));
vm_phys_free_contig(&rv->pages[begin_zeroes], NBPOPMAP * i +
hi - begin_zeroes);
vm_domain_free_unlock(VM_DOMAIN(rv->domain));
} while (i < NPOPMAP);
KASSERT(rv->popcnt == 0,
("vm_reserv_break: reserv %p's popcnt is corrupted", rv));
}
rv->popcnt = 0;
counter_u64_add(vm_reserv_broken, 1);
}