Author: dougm Date: Tue May 28 00:51:23 2019 New Revision: 348318 URL: https://svnweb.freebsd.org/changeset/base/348318
Log: Reduce the code size and number of ffsl calls in vm_reserv_break. Use 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 Modified: head/sys/vm/vm_reserv.c Modified: head/sys/vm/vm_reserv.c ============================================================================== --- head/sys/vm/vm_reserv.c Tue May 28 00:03:46 2019 (r348317) +++ head/sys/vm/vm_reserv.c Tue May 28 00:51:23 2019 (r348318) @@ -1030,56 +1030,49 @@ vm_reserv_alloc_page(int req, vm_object_t object, vm_p 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); } _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
