#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <string.h>
#include <sys/mman.h>
#include <errno.h>
#include "meta.h"
LOCK_OBJ_DEF;
const uint16_t size_classes[] = {
1, 2, 3, 4, 5, 6, 7, 8,
9, 10, 12, 15,
18, 20, 25, 31,
36, 42, 50, 63,
72, 84, 102, 127,
146, 170, 204, 255,
292, 340, 409, 511,
584, 682, 818, 1023,
1169, 1364, 1637, 2047,
2340, 2730, 3276, 4095,
4680, 5460, 6552, 8191,
};
static const uint8_t small_cnt_tab[][3] = {
{ 30, 30, 30 },
{ 31, 15, 15 },
{ 20, 10, 10 },
{ 31, 15, 7 },
{ 25, 12, 6 },
{ 21, 10, 5 },
{ 18, 8, 4 },
{ 31, 15, 7 },
{ 28, 14, 6 },
};
static const uint8_t med_cnt_tab[4] = { 28, 24, 20, 32 };
struct malloc_context ctx = { 0 };
struct meta *alloc_meta(void)
{
struct meta *m;
unsigned char *p;
if (!ctx.init_done) {
#ifndef PAGESIZE
ctx.pagesize = get_page_size();
#endif
ctx.secret = get_random_secret();
ctx.init_done = 1;
}
size_t pagesize = PGSZ;
if (pagesize < 4096) pagesize = 4096;
if ((m = dequeue_head(&ctx.free_meta_head))) return m;
if (!ctx.avail_meta_count) {
int need_unprotect = 1;
if (!ctx.avail_meta_area_count && ctx.brk!=-1) {
uintptr_t new = ctx.brk + pagesize;
int need_guard = 0;
if (!ctx.brk) {
need_guard = 1;
ctx.brk = brk(0);
// some ancient kernels returned _ebss
// instead of next page as initial brk.
ctx.brk += -ctx.brk & (pagesize-1);
new = ctx.brk + 2*pagesize;
}
if (brk(new) != new) {
ctx.brk = -1;
} else {
if (need_guard) mmap((void *)ctx.brk, pagesize,
PROT_NONE, MAP_ANON|MAP_PRIVATE|MAP_FIXED, -1, 0);
ctx.brk = new;
ctx.avail_meta_areas = (void *)(new - pagesize);
ctx.avail_meta_area_count = pagesize>>12;
need_unprotect = 0;
}
}
if (!ctx.avail_meta_area_count) {
size_t n = 2UL << ctx.meta_alloc_shift;
p = mmap(0, n*pagesize, PROT_NONE,
MAP_PRIVATE|MAP_ANON, -1, 0);
if (p==MAP_FAILED) return 0;
ctx.avail_meta_areas = p + pagesize;
ctx.avail_meta_area_count = (n-1)*(pagesize>>12);
ctx.meta_alloc_shift++;
}
p = ctx.avail_meta_areas;
if ((uintptr_t)p & (pagesize-1)) need_unprotect = 0;
if (need_unprotect)
if (mprotect(p, pagesize, PROT_READ|PROT_WRITE)
&& errno != ENOSYS)
return 0;
ctx.avail_meta_area_count--;
ctx.avail_meta_areas = p + 4096;
if (ctx.meta_area_tail) {
ctx.meta_area_tail->next = (void *)p;
} else {
ctx.meta_area_head = (void *)p;
}
ctx.meta_area_tail = (void *)p;
ctx.meta_area_tail->check = ctx.secret;
ctx.avail_meta_count = ctx.meta_area_tail->nslots
= (4096-sizeof(struct meta_area))/sizeof *m;
ctx.avail_meta = ctx.meta_area_tail->slots;
}
ctx.avail_meta_count--;
m = ctx.avail_meta++;
m->prev = m->next = 0;
return m;
}
static uint32_t try_avail(struct meta **pm)
{
struct meta *m = *pm;
uint32_t first;
if (!m) return 0;
uint32_t mask = m->avail_mask;
if (!mask) {
if (!m) return 0;
if (!m->freed_mask) {
dequeue(pm, m);
m = *pm;
if (!m) return 0;
} else {
m = m->next;
*pm = m;
}
mask = m->freed_mask;
// skip fully-free group unless it's the only one
// or it's a permanently non-freeable group
if (mask == (2u<<m->last_idx)-1 && m->freeable) {
m = m->next;
*pm = m;
mask = m->freed_mask;
}
// activate more slots in a not-fully-active group
// if needed, but only as a last resort. prefer using
// any other group with free slots. this avoids
// touching & dirtying as-yet-unused pages.
if (!(mask & ((2u<<m->mem->active_idx)-1))) {
if (m->next != m) {
m = m->next;
*pm = m;
} else {
int cnt = m->mem->active_idx + 2;
int size = size_classes[m->sizeclass]*UNIT;
int span = UNIT + size*cnt;
// activate up to next 4k boundary
while ((span^(span+size-1)) < 4096) {
cnt++;
span += size;
}
if (cnt > m->last_idx+1)
cnt = m->last_idx+1;
m->mem->active_idx = cnt-1;
}
}
mask = activate_group(m);
assert(mask);
decay_bounces(m->sizeclass);
}
first = mask&-mask;
m->avail_mask = mask-first;
return first;
}
static int alloc_slot(int, size_t);
static struct meta *alloc_group(int sc, size_t req)
{
size_t size = UNIT*size_classes[sc];
int i = 0, cnt;
unsigned char *p;
struct meta *m = alloc_meta();
if (!m) return 0;
size_t usage = ctx.usage_by_class[sc];
size_t pagesize = PGSZ;
int active_idx;
if (sc < 9) {
while (i<2 && 4*small_cnt_tab[sc][i] > usage)
i++;
cnt = small_cnt_tab[sc][i];
} else {
// lookup max number of slots fitting in power-of-two size
// from a table, along with number of factors of two we
// can divide out without a remainder or reaching 1.
cnt = med_cnt_tab[sc&3];
// reduce cnt to avoid excessive eagar allocation.
while (!(cnt&1) && 4*cnt > usage)
cnt >>= 1;
// data structures don't support groups whose slot offsets
// in units don't fit in 16 bits.
while (size*cnt >= 65536*UNIT)
cnt >>= 1;
}
// If we selected a count of 1 above but it's not sufficient to use
// mmap, increase to 2. Then it might be; if not it will nest.
if (cnt==1 && size*cnt+UNIT <= pagesize/2) cnt = 2;
// All choices of size*cnt are "just below" a power of two, so anything
// larger than half the page size should be allocated as whole pages.
if (size*cnt+UNIT > pagesize/2) {
// check/update bounce counter to start/increase retention
// of freed maps, and inhibit use of low-count, odd-size
// small mappings and single-slot groups if activated.
int nosmall = is_bouncing(sc);
account_bounce(sc);
step_seq();
// since the following count reduction opportunities have
// an absolute memory usage cost, don't overdo them. count
// coarse usage as part of usage.
if (!(sc&1) && sc<32) usage += ctx.usage_by_class[sc+1];
// try to drop to a lower count if the one found above
// increases usage by more than 25%. these reduced counts
// roughly fill an integral number of pages, just not a
// power of two, limiting amount of unusable space.
if (4*cnt > usage && !nosmall) {
if (0);
else if ((sc&3)==1 && size*cnt>8*pagesize) cnt = 2;
else if ((sc&3)==2 && size*cnt>4*pagesize) cnt = 3;
else if ((sc&3)==0 && size*cnt>8*pagesize) cnt = 3;
else if ((sc&3)==0 && size*cnt>2*pagesize) cnt = 5;
}
size_t needed = size*cnt + UNIT;
needed += -needed & (pagesize-1);
// produce an individually-mmapped allocation if usage is low,
// bounce counter hasn't triggered, and either it saves memory
// or it avoids eagar slot allocation without wasting too much.
if (!nosmall && cnt<=7) {
req += IB + UNIT;
req += -req & (pagesize-1);
if (req<size+UNIT || (req>=4*pagesize && 2*cnt>usage)) {
cnt = 1;
needed = req;
}
}
p = mmap(0, needed, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
if (p==MAP_FAILED) {
free_meta(m);
return 0;
}
m->maplen = needed>>12;
ctx.mmap_counter++;
active_idx = (4096-UNIT)/size-1;
if (active_idx > cnt-1) active_idx = cnt-1;
if (active_idx < 0) active_idx = 0;
} else {
int j = size_to_class(UNIT+cnt*size-IB);
int idx = alloc_slot(j, UNIT+cnt*size-IB);
if (idx < 0) {
free_meta(m);
return 0;
}
struct meta *g = ctx.active[j];
p = enframe(g, idx, UNIT*size_classes[j]-IB, ctx.mmap_counter);
m->maplen = 0;
p[-3] = (p[-3]&31) | (6<<5);
for (int i=0; i<=cnt; i++)
p[UNIT+i*size-4] = 0;
active_idx = cnt-1;
}
ctx.usage_by_class[sc] += cnt;
m->avail_mask = (2u<<active_idx)-1;
m->freed_mask = (2u<<(cnt-1))-1 - m->avail_mask;
m->mem = (void *)p;
m->mem->meta = m;
m->mem->active_idx = active_idx;
m->last_idx = cnt-1;
m->freeable = 1;
m->sizeclass = sc;
return m;
}
static int alloc_slot(int sc, size_t req)
{
uint32_t first = try_avail(&ctx.active[sc]);
if (first) return a_ctz_32(first);
struct meta *g = alloc_group(sc, req);
if (!g) return -1;
g->avail_mask--;
queue(&ctx.active[sc], g);
return 0;
}
void *malloc(size_t n)
{
if (size_overflows(n)) return 0;
struct meta *g;
uint32_t mask, first;
int sc;
int idx;
int ctr;
if (n >= MMAP_THRESHOLD) {
size_t needed = n + IB + UNIT;
void *p = mmap(0, needed, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANON, -1, 0);
if (p==MAP_FAILED) return 0;
wrlock();
step_seq();
g = alloc_meta();
if (!g) {
unlock();
munmap(p, needed);
return 0;
}
g->mem = p;
g->mem->meta = g;
g->last_idx = 0;
g->freeable = 1;
g->sizeclass = 63;
g->maplen = (needed+4095)/4096;
g->avail_mask = g->freed_mask = 0;
// use a global counter to cycle offset in
// individually-mmapped allocations.
ctx.mmap_counter++;
idx = 0;
goto success;
}
sc = size_to_class(n);
rdlock();
g = ctx.active[sc];
// use coarse size classes initially when there are not yet
// any groups of desired size. this allows counts of 2 or 3
// to be allocated at first rather than having to start with
// 7 or 5, the min counts for even size classes.
if (!g && sc>=4 && sc<32 && sc!=6 && !(sc&1) && !ctx.usage_by_class[sc]) {
size_t usage = ctx.usage_by_class[sc|1];
// if a new group may be allocated, count it toward
// usage in deciding if we can use coarse class.
if (!ctx.active[sc|1] || (!ctx.active[sc|1]->avail_mask
&& !ctx.active[sc|1]->freed_mask))
usage += 3;
if (usage <= 12)
sc |= 1;
g = ctx.active[sc];
}
for (;;) {
mask = g ? g->avail_mask : 0;
first = mask&-mask;
if (!first) break;
if (RDLOCK_IS_EXCLUSIVE || !MT)
g->avail_mask = mask-first;
else if (a_cas(&g->avail_mask, mask, mask-first)!=mask)
continue;
idx = a_ctz_32(first);
goto success;
}
upgradelock();
idx = alloc_slot(sc, n);
if (idx < 0) {
unlock();
return 0;
}
g = ctx.active[sc];
success:
ctr = ctx.mmap_counter;
unlock();
return enframe(g, idx, n, ctr);
}
int is_allzero(void *p)
{
struct meta *g = get_meta(p);
return g->sizeclass >= 48 ||
get_stride(g) < UNIT*size_classes[g->sizeclass];
}
