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os_kernel_lab/code/lab7/kern/mm/kmalloc.c

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#include <defs.h>
#include <list.h>
#include <memlayout.h>
#include <assert.h>
#include <kmalloc.h>
#include <sync.h>
#include <pmm.h>
#include <stdio.h>
#include <rb_tree.h>
/* The slab allocator used in ucore is based on an algorithm first introduced by
Jeff Bonwick for the SunOS operating system. The paper can be download from
http://citeseer.ist.psu.edu/bonwick94slab.html
An implementation of the Slab Allocator as described in outline in;
UNIX Internals: The New Frontiers by Uresh Vahalia
Pub: Prentice Hall ISBN 0-13-101908-2
Within a kernel, a considerable amount of memory is allocated for a finite set
of objects such as file descriptors and other common structures. Jeff found that
the amount of time required to initialize a regular object in the kernel exceeded
the amount of time required to allocate and deallocate it. His conclusion was
that instead of freeing the memory back to a global pool, he would have the memory
remain initialized for its intended purpose.
In our simple slab implementation, the the high-level organization of the slab
structures is simplied. At the highest level is an array slab_cache[SLAB_CACHE_NUM],
and each array element is a slab_cache which has slab chains. Each slab_cache has
two list, one list chains the full allocated slab, and another list chains the notfull
allocated(maybe empty) slab. And each slab has fixed number(2^n) of pages. In each
slab, there are a lot of objects (such as ) with same fixed size(32B ~ 128KB).
+----------------------------------+
| slab_cache[0] for 0~32B obj |
+----------------------------------+
| slab_cache[1] for 33B~64B obj |-->lists for slabs
+----------------------------------+ |
| slab_cache[2] for 65B~128B obj | |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
+----------------------------------+ |
| slab_cache[12]for 64KB~128KB obj | |
+----------------------------------+ |
|
slabs_full/slabs_not +---------------------+
-<-----------<----------<-+
| | |
slab1 slab2 slab3...
|
|-------|-------|
pages1 pages2 pages3...
|
|
|
slab_t+n*bufctl_t+obj1-obj2-obj3...objn (the size of obj is small)
|
OR
|
obj1-obj2-obj3...objn WITH slab_t+n*bufctl_t in another slab (the size of obj is BIG)
The important functions are:
kmem_cache_grow(kmem_cache_t *cachep)
kmem_slab_destroy(kmem_cache_t *cachep, slab_t *slabp)
kmalloc(size_t size): used by outside functions need dynamicly get memory
kfree(void *objp): used by outside functions need dynamicly release memory
*/
#define BUFCTL_END 0xFFFFFFFFL // the signature of the last bufctl
#define SLAB_LIMIT 0xFFFFFFFEL // the max value of obj number
typedef size_t kmem_bufctl_t; //the index of obj in slab
typedef struct slab_s {
list_entry_t slab_link; // the list entry linked to kmem_cache list
void *s_mem; // the kernel virtual address of the first obj in slab
size_t inuse; // the number of allocated objs
size_t offset; // the first obj's offset value in slab
kmem_bufctl_t free; // the first free obj's index in slab
} slab_t;
// get the slab address according to the link element (see list.h)
#define le2slab(le, member) \
to_struct((le), slab_t, member)
typedef struct kmem_cache_s kmem_cache_t;
struct kmem_cache_s {
list_entry_t slabs_full; // list for fully allocated slabs
list_entry_t slabs_notfull; // list for not-fully allocated slabs
size_t objsize; // the fixed size of obj
size_t num; // number of objs per slab
size_t offset; // this first obj's offset in slab
bool off_slab; // the control part of slab in slab or not.
/* order of pages per slab (2^n) */
size_t page_order;
kmem_cache_t *slab_cachep;
};
#define MIN_SIZE_ORDER 5 // 32
#define MAX_SIZE_ORDER 17 // 128k
#define SLAB_CACHE_NUM (MAX_SIZE_ORDER - MIN_SIZE_ORDER + 1)
static kmem_cache_t slab_cache[SLAB_CACHE_NUM];
static void init_kmem_cache(kmem_cache_t *cachep, size_t objsize, size_t align);
static void check_slab(void);
//slab_init - call init_kmem_cache function to reset the slab_cache array
static void
slab_init(void) {
size_t i;
//the align bit for obj in slab. 2^n could be better for performance
size_t align = 16;
for (i = 0; i < SLAB_CACHE_NUM; i ++) {
init_kmem_cache(slab_cache + i, 1 << (i + MIN_SIZE_ORDER), align);
}
check_slab();
}
inline void
kmalloc_init(void) {
slab_init();
cprintf("kmalloc_init() succeeded!\n");
}
//slab_allocated - summary the total size of allocated objs
static size_t
slab_allocated(void) {
size_t total = 0;
int i;
bool intr_flag;
local_intr_save(intr_flag);
{
for (i = 0; i < SLAB_CACHE_NUM; i ++) {
kmem_cache_t *cachep = slab_cache + i;
list_entry_t *list, *le;
list = le = &(cachep->slabs_full);
while ((le = list_next(le)) != list) {
total += cachep->num * cachep->objsize;
}
list = le = &(cachep->slabs_notfull);
while ((le = list_next(le)) != list) {
slab_t *slabp = le2slab(le, slab_link);
total += slabp->inuse * cachep->objsize;
}
}
}
local_intr_restore(intr_flag);
return total;
}
inline size_t
kallocated(void) {
return slab_allocated();
}
// slab_mgmt_size - get the size of slab control area (slab_t+num*kmem_bufctl_t)
static size_t
slab_mgmt_size(size_t num, size_t align) {
return ROUNDUP(sizeof(slab_t) + num * sizeof(kmem_bufctl_t), align);
}
// cacahe_estimate - estimate the number of objs in a slab
static void
cache_estimate(size_t order, size_t objsize, size_t align, bool off_slab, size_t *remainder, size_t *num) {
size_t nr_objs, mgmt_size;
size_t slab_size = (PGSIZE << order);
if (off_slab) {
mgmt_size = 0;
nr_objs = slab_size / objsize;
if (nr_objs > SLAB_LIMIT) {
nr_objs = SLAB_LIMIT;
}
}
else {
nr_objs = (slab_size - sizeof(slab_t)) / (objsize + sizeof(kmem_bufctl_t));
while (slab_mgmt_size(nr_objs, align) + nr_objs * objsize > slab_size) {
nr_objs --;
}
if (nr_objs > SLAB_LIMIT) {
nr_objs = SLAB_LIMIT;
}
mgmt_size = slab_mgmt_size(nr_objs, align);
}
*num = nr_objs;
*remainder = slab_size - nr_objs * objsize - mgmt_size;
}
// calculate_slab_order - estimate the size(4K~4M) of slab
// paramemters:
// cachep: the slab_cache
// objsize: the size of obj
// align: align bit for objs
// off_slab: the control part of slab in slab or not
// left_over: the size of can not be used area in slab
static void
calculate_slab_order(kmem_cache_t *cachep, size_t objsize, size_t align, bool off_slab, size_t *left_over) {
size_t order;
for (order = 0; order <= KMALLOC_MAX_ORDER; order ++) {
size_t num, remainder;
cache_estimate(order, objsize, align, off_slab, &remainder, &num);
if (num != 0) {
if (off_slab) {
size_t off_slab_limit = objsize - sizeof(slab_t);
off_slab_limit /= sizeof(kmem_bufctl_t);
if (num > off_slab_limit) {
panic("off_slab: objsize = %d, num = %d.", objsize, num);
}
}
if (remainder * 8 <= (PGSIZE << order)) {
cachep->num = num;
cachep->page_order = order;
if (left_over != NULL) {
*left_over = remainder;
}
return ;
}
}
}
panic("calculate_slab_over: failed.");
}
// getorder - find order, should satisfy n <= minest 2^order
static inline size_t
getorder(size_t n) {
size_t order = MIN_SIZE_ORDER, order_size = (1 << order);
for (; order <= MAX_SIZE_ORDER; order ++, order_size <<= 1) {
if (n <= order_size) {
return order;
}
}
panic("getorder failed. %d\n", n);
}
// init_kmem_cache - initial a slab_cache cachep according to the obj with the size = objsize
static void
init_kmem_cache(kmem_cache_t *cachep, size_t objsize, size_t align) {
list_init(&(cachep->slabs_full));
list_init(&(cachep->slabs_notfull));
objsize = ROUNDUP(objsize, align);
cachep->objsize = objsize;
cachep->off_slab = (objsize >= (PGSIZE >> 3));
size_t left_over;
calculate_slab_order(cachep, objsize, align, cachep->off_slab, &left_over);
assert(cachep->num > 0);
size_t mgmt_size = slab_mgmt_size(cachep->num, align);
if (cachep->off_slab && left_over >= mgmt_size) {
cachep->off_slab = 0;
}
if (cachep->off_slab) {
cachep->offset = 0;
cachep->slab_cachep = slab_cache + (getorder(mgmt_size) - MIN_SIZE_ORDER);
}
else {
cachep->offset = mgmt_size;
}
}
static void *kmem_cache_alloc(kmem_cache_t *cachep);
#define slab_bufctl(slabp) \
((kmem_bufctl_t*)(((slab_t *)(slabp)) + 1))
// kmem_cache_slabmgmt - get the address of a slab according to page
// - and initialize the slab according to cachep
static slab_t *
kmem_cache_slabmgmt(kmem_cache_t *cachep, struct Page *page) {
void *objp = page2kva(page);
slab_t *slabp;
if (cachep->off_slab) {
if ((slabp = kmem_cache_alloc(cachep->slab_cachep)) == NULL) {
return NULL;
}
}
else {
slabp = page2kva(page);
}
slabp->inuse = 0;
slabp->offset = cachep->offset;
slabp->s_mem = objp + cachep->offset;
return slabp;
}
#define SET_PAGE_CACHE(page, cachep) \
do { \
struct Page *__page = (struct Page *)(page); \
kmem_cache_t **__cachepp = (kmem_cache_t **)&(__page->page_link.next); \
*__cachepp = (kmem_cache_t *)(cachep); \
} while (0)
#define SET_PAGE_SLAB(page, slabp) \
do { \
struct Page *__page = (struct Page *)(page); \
slab_t **__cachepp = (slab_t **)&(__page->page_link.prev); \
*__cachepp = (slab_t *)(slabp); \
} while (0)
// kmem_cache_grow - allocate a new slab by calling alloc_pages
// - set control area in the new slab
static bool
kmem_cache_grow(kmem_cache_t *cachep) {
struct Page *page = alloc_pages(1 << cachep->page_order);
if (page == NULL) {
goto failed;
}
slab_t *slabp;
if ((slabp = kmem_cache_slabmgmt(cachep, page)) == NULL) {
goto oops;
}
size_t order_size = (1 << cachep->page_order);
do {
//setup this page in the free list (see memlayout.h: struct page)???
SET_PAGE_CACHE(page, cachep);
SET_PAGE_SLAB(page, slabp);
//this page is used for slab
SetPageSlab(page);
page ++;
} while (-- order_size);
int i;
for (i = 0; i < cachep->num; i ++) {
slab_bufctl(slabp)[i] = i + 1;
}
slab_bufctl(slabp)[cachep->num - 1] = BUFCTL_END;
slabp->free = 0;
bool intr_flag;
local_intr_save(intr_flag);
{
list_add(&(cachep->slabs_notfull), &(slabp->slab_link));
}
local_intr_restore(intr_flag);
return 1;
oops:
free_pages(page, 1 << cachep->page_order);
failed:
return 0;
}
// kmem_cache_alloc_one - allocate a obj in a slab
static void *
kmem_cache_alloc_one(kmem_cache_t *cachep, slab_t *slabp) {
slabp->inuse ++;
void *objp = slabp->s_mem + slabp->free * cachep->objsize;
slabp->free = slab_bufctl(slabp)[slabp->free];
if (slabp->free == BUFCTL_END) {
list_del(&(slabp->slab_link));
list_add(&(cachep->slabs_full), &(slabp->slab_link));
}
return objp;
}
// kmem_cache_alloc - call kmem_cache_alloc_one function to allocate a obj
// - if no free obj, try to allocate a slab
static void *
kmem_cache_alloc(kmem_cache_t *cachep) {
void *objp;
bool intr_flag;
try_again:
local_intr_save(intr_flag);
if (list_empty(&(cachep->slabs_notfull))) {
goto alloc_new_slab;
}
slab_t *slabp = le2slab(list_next(&(cachep->slabs_notfull)), slab_link);
objp = kmem_cache_alloc_one(cachep, slabp);
local_intr_restore(intr_flag);
return objp;
alloc_new_slab:
local_intr_restore(intr_flag);
if (kmem_cache_grow(cachep)) {
goto try_again;
}
return NULL;
}
// kmalloc - simple interface used by outside functions
// - to allocate a free memory using kmem_cache_alloc function
void *
kmalloc(size_t size) {
assert(size > 0);
size_t order = getorder(size);
if (order > MAX_SIZE_ORDER) {
return NULL;
}
return kmem_cache_alloc(slab_cache + (order - MIN_SIZE_ORDER));
}
static void kmem_cache_free(kmem_cache_t *cachep, void *obj);
// kmem_slab_destroy - call free_pages & kmem_cache_free to free a slab
static void
kmem_slab_destroy(kmem_cache_t *cachep, slab_t *slabp) {
struct Page *page = kva2page(slabp->s_mem - slabp->offset);
struct Page *p = page;
size_t order_size = (1 << cachep->page_order);
do {
assert(PageSlab(p));
ClearPageSlab(p);
p ++;
} while (-- order_size);
free_pages(page, 1 << cachep->page_order);
if (cachep->off_slab) {
kmem_cache_free(cachep->slab_cachep, slabp);
}
}
// kmem_cache_free_one - free an obj in a slab
// - if slab->inuse==0, then free the slab
static void
kmem_cache_free_one(kmem_cache_t *cachep, slab_t *slabp, void *objp) {
//should not use divide operator ???
size_t objnr = (objp - slabp->s_mem) / cachep->objsize;
slab_bufctl(slabp)[objnr] = slabp->free;
slabp->free = objnr;
slabp->inuse --;
if (slabp->inuse == 0) {
list_del(&(slabp->slab_link));
kmem_slab_destroy(cachep, slabp);
}
else if (slabp->inuse == cachep->num -1 ) {
list_del(&(slabp->slab_link));
list_add(&(cachep->slabs_notfull), &(slabp->slab_link));
}
}
#define GET_PAGE_CACHE(page) \
(kmem_cache_t *)((page)->page_link.next)
#define GET_PAGE_SLAB(page) \
(slab_t *)((page)->page_link.prev)
// kmem_cache_free - call kmem_cache_free_one function to free an obj
static void
kmem_cache_free(kmem_cache_t *cachep, void *objp) {
bool intr_flag;
struct Page *page = kva2page(objp);
if (!PageSlab(page)) {
panic("not a slab page %08x\n", objp);
}
local_intr_save(intr_flag);
{
kmem_cache_free_one(cachep, GET_PAGE_SLAB(page), objp);
}
local_intr_restore(intr_flag);
}
// kfree - simple interface used by ooutside functions to free an obj
void
kfree(void *objp) {
kmem_cache_free(GET_PAGE_CACHE(kva2page(objp)), objp);
}
static inline void
check_slab_empty(void) {
int i;
for (i = 0; i < SLAB_CACHE_NUM; i ++) {
kmem_cache_t *cachep = slab_cache + i;
assert(list_empty(&(cachep->slabs_full)));
assert(list_empty(&(cachep->slabs_notfull)));
}
}
void
check_slab(void) {
int i;
void *v0, *v1;
size_t nr_free_pages_store = nr_free_pages();
size_t kernel_allocated_store = slab_allocated();
/* slab must be empty now */
check_slab_empty();
assert(slab_allocated() == 0);
kmem_cache_t *cachep0, *cachep1;
cachep0 = slab_cache;
assert(cachep0->objsize == 32 && cachep0->num > 1 && !cachep0->off_slab);
assert((v0 = kmalloc(16)) != NULL);
slab_t *slabp0, *slabp1;
assert(!list_empty(&(cachep0->slabs_notfull)));
slabp0 = le2slab(list_next(&(cachep0->slabs_notfull)), slab_link);
assert(slabp0->inuse == 1 && list_next(&(slabp0->slab_link)) == &(cachep0->slabs_notfull));
struct Page *p0, *p1;
size_t order_size;
p0 = kva2page(slabp0->s_mem - slabp0->offset), p1 = p0;
order_size = (1 << cachep0->page_order);
for (i = 0; i < cachep0->page_order; i ++, p1 ++) {
assert(PageSlab(p1));
assert(GET_PAGE_CACHE(p1) == cachep0 && GET_PAGE_SLAB(p1) == slabp0);
}
assert(v0 == slabp0->s_mem);
assert((v1 = kmalloc(16)) != NULL && v1 == v0 + 32);
kfree(v0);
assert(slabp0->free == 0);
kfree(v1);
assert(list_empty(&(cachep0->slabs_notfull)));
for (i = 0; i < cachep0->page_order; i ++, p0 ++) {
assert(!PageSlab(p0));
}
v0 = kmalloc(16);
assert(!list_empty(&(cachep0->slabs_notfull)));
slabp0 = le2slab(list_next(&(cachep0->slabs_notfull)), slab_link);
for (i = 0; i < cachep0->num - 1; i ++) {
kmalloc(16);
}
assert(slabp0->inuse == cachep0->num);
assert(list_next(&(cachep0->slabs_full)) == &(slabp0->slab_link));
assert(list_empty(&(cachep0->slabs_notfull)));
v1 = kmalloc(16);
assert(!list_empty(&(cachep0->slabs_notfull)));
slabp1 = le2slab(list_next(&(cachep0->slabs_notfull)), slab_link);
kfree(v0);
assert(list_empty(&(cachep0->slabs_full)));
assert(list_next(&(slabp0->slab_link)) == &(slabp1->slab_link)
|| list_next(&(slabp1->slab_link)) == &(slabp0->slab_link));
kfree(v1);
assert(!list_empty(&(cachep0->slabs_notfull)));
assert(list_next(&(cachep0->slabs_notfull)) == &(slabp0->slab_link));
assert(list_next(&(slabp0->slab_link)) == &(cachep0->slabs_notfull));
v1 = kmalloc(16);
assert(v1 == v0);
assert(list_next(&(cachep0->slabs_full)) == &(slabp0->slab_link));
assert(list_empty(&(cachep0->slabs_notfull)));
for (i = 0; i < cachep0->num; i ++) {
kfree(v1 + i * cachep0->objsize);
}
assert(list_empty(&(cachep0->slabs_full)));
assert(list_empty(&(cachep0->slabs_notfull)));
cachep0 = slab_cache;
bool has_off_slab = 0;
for (i = 0; i < SLAB_CACHE_NUM; i ++, cachep0 ++) {
if (cachep0->off_slab) {
has_off_slab = 1;
cachep1 = cachep0->slab_cachep;
if (!cachep1->off_slab) {
break;
}
}
}
if (!has_off_slab) {
goto check_pass;
}
assert(cachep0->off_slab && !cachep1->off_slab);
assert(cachep1 < cachep0);
assert(list_empty(&(cachep0->slabs_full)));
assert(list_empty(&(cachep0->slabs_notfull)));
assert(list_empty(&(cachep1->slabs_full)));
assert(list_empty(&(cachep1->slabs_notfull)));
v0 = kmalloc(cachep0->objsize);
p0 = kva2page(v0);
assert(page2kva(p0) == v0);
if (cachep0->num == 1) {
assert(!list_empty(&(cachep0->slabs_full)));
slabp0 = le2slab(list_next(&(cachep0->slabs_full)), slab_link);
}
else {
assert(!list_empty(&(cachep0->slabs_notfull)));
slabp0 = le2slab(list_next(&(cachep0->slabs_notfull)), slab_link);
}
assert(slabp0 != NULL);
if (cachep1->num == 1) {
assert(!list_empty(&(cachep1->slabs_full)));
slabp1 = le2slab(list_next(&(cachep1->slabs_full)), slab_link);
}
else {
assert(!list_empty(&(cachep1->slabs_notfull)));
slabp1 = le2slab(list_next(&(cachep1->slabs_notfull)), slab_link);
}
assert(slabp1 != NULL);
order_size = (1 << cachep0->page_order);
for (i = 0; i < order_size; i ++, p0 ++) {
assert(PageSlab(p0));
assert(GET_PAGE_CACHE(p0) == cachep0 && GET_PAGE_SLAB(p0) == slabp0);
}
kfree(v0);
check_pass:
check_rb_tree();
check_slab_empty();
assert(slab_allocated() == 0);
assert(nr_free_pages_store == nr_free_pages());
assert(kernel_allocated_store == slab_allocated());
cprintf("check_slab() succeeded!\n");
}
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