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#include <kernel/arch/generic.h>
#include <kernel/malloc.h>
#include <kernel/panic.h>
#include <kernel/util.h>
#include <shared/mem.h>
#include <stdbool.h>
#include <stdint.h>
#define DESCLEN 8
#define SCMIN 6 /* 1<<6 == 64 */
#define SCMAX 12 /* 1<<11 == 2048 */
typedef struct Slab Slab;
struct Slab {
/* The slab is divided up into 1<<sizeclass sized regions.
* SCMIN <= sizeclass < SCMAX */
int sizeclass;
/* Conveniently, 4096/64 = 64, so I can fit the entire region bitmap
* in a word. */
uint64_t bitmap;
Slab **slot, *next;
};
/* The code assumes the header fits within the first region. */
static_assert(sizeof(Slab) <= 1<<SCMIN);
/* Yes, I'm wasting a bit of memory here. */
static Slab *freeslabs[SCMAX] = {NULL};
static Slab *fullslabs[SCMAX] = {NULL};
static uint64_t curslabs = 0;
static uint64_t
findfreebit(uint64_t bitmap)
{
/* I'm hoping gcc is smart enough to optimize this into a BSF */
bitmap = ~bitmap;
for (uint64_t i = 0; i < 64; i++) {
if (bitmap & (1ull<<i)) return i;
}
return 64;
}
static bool
isfull(uint64_t bitmap, int sizeclass)
{
return findfreebit(bitmap)<<sizeclass == PAGE_SIZE;
}
static uint64_t
crawllist(Slab *al, int sizeclass, bool full)
{
(void) full;
uint64_t tally = 0;
int regsize = 1ull << sizeclass;
for (; al; al = al->next) {
kprintf(
"%08p %016llx %s %d\n",
al, al->bitmap, full ? "full" : "part", 1ull<<al->sizeclass
);
assert(al->sizeclass == sizeclass);
assert(al->bitmap & 1);
assert(al->slot && *al->slot == al);
assert(isfull(al->bitmap, sizeclass) == full);
tally++;
for (int i = 1; i * regsize < PAGE_SIZE; i++) {
char *p = ((char*)al) + i * regsize;
if (al->bitmap & (1ull<<i)) {
kprintf("%08p %.8s\n", p, p + regsize - DESCLEN);
}
}
}
return tally;
}
void
kmalloc_debugprint(void)
{
uint64_t tally = 0;
for (int i = 0; i < SCMAX; i++) {
tally += crawllist(freeslabs[i], i, false);
tally += crawllist(fullslabs[i], i, true);
}
assert(tally == curslabs);
// TODO count waste
}
static int
getsizeclass(size_t len)
{
int i;
for (i = SCMIN; i < SCMAX-1; i++) { /* last iteration can be skipped */
if (len <= (1ull<<i)) break;
}
assert(len <= (1ull<<i));
return i;
}
static Slab *
getheader(void *addr)
{
Slab *hdr = (void*)((uintptr_t)addr & ~PAGE_MASK);
assert(SCMIN <= hdr->sizeclass && hdr->sizeclass < SCMAX);
assert(hdr->bitmap & 1);
return hdr;
}
void *
kmalloc(size_t len, const char *desc)
{
Slab *al;
void *ret;
int sizeclass, regsize;
uint64_t idx;
assert(len <= KMALLOC_MAX);
len += DESCLEN;
sizeclass = getsizeclass(len);
regsize = 1ull << sizeclass;
if (freeslabs[sizeclass] == NULL) {
al = page_alloc(1);
al->sizeclass = sizeclass;
al->bitmap = 1; /* mark header as allocated */
al->slot = &freeslabs[sizeclass];
al->next = NULL;
freeslabs[sizeclass] = al;
curslabs++;
}
al = freeslabs[sizeclass];
idx = findfreebit(al->bitmap);
assert(1 <= idx && idx < 64);
assert((al->bitmap & (1ull<<idx)) == 0);
assert(regsize * idx < PAGE_SIZE);
ret = ((char*)al) + regsize * idx;
al->bitmap |= 1ull<<idx;
char *descloc = ret + regsize - DESCLEN;
memset(descloc, ' ', DESCLEN);
for (int i = 0; i < DESCLEN && desc[i]; i++) {
descloc[i] = desc[i];
}
/* if this was the last free region, move to fullslabs */
if (isfull(al->bitmap, sizeclass)) {
*al->slot = al->next;
al->next->slot = al->slot;
al->next = fullslabs[sizeclass];
al->next->slot = &al->next;
fullslabs[sizeclass] = al;
al->slot = &fullslabs[sizeclass];
}
return ret;
}
void
kfree(void *ptr)
{
assert(ptr);
Slab *al = getheader(ptr);
int sizeclass = al->sizeclass;
int regsize = 1ull << sizeclass;
uint64_t off = ((uint64_t)ptr) & PAGE_MASK;
uint64_t idx = off >> sizeclass;
bool full = isfull(al->bitmap, sizeclass);
assert(((char*)al) + idx * regsize == ptr); /* aligned? */
assert(1 <= idx); /* not the header? */
assert(al->bitmap & (1ull<<idx)); /* actually allocated? */
al->bitmap &= ~(1ull<<idx);
memset(ptr, 0xCC, regsize);
if (al->bitmap == 1) { /* we're empty */
*al->slot = al->next;
al->next->slot = al->slot;
page_free(al, 1);
curslabs--;
} else if (full) { /* we're no longer full */
*al->slot = al->next;
al->next->slot = al->slot;
al->next = freeslabs[sizeclass];
al->next->slot = &al->next;
freeslabs[sizeclass] = al;
al->slot = &freeslabs[sizeclass];
assert(fullslabs[sizeclass] != al);
}
}
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