bird/lib/slab.c
Toke Høiland-Jørgensen db2d29073a lib/slab: introduce sl_allocz() function and use it in Babel
The babel protocol code was initialising objects returned from the slab
allocator by assigning to each of the struct members individually, but
wasn't touching the NODE member while doing so. This leads to warnings on
debug builds since commit:

baac700906 ("List expensive check.")

To fix this, introduce an sl_allocz() variant of the slab allocator which
will zero out the memory before returning it, and switch all the babel call
sites to use this version. The overhead for doing this should be negligible
for small objects, and in the case of babel, the largest object being
allocated was being zeroed anyway, so we can drop the memset in
babel_read_tlv().
2020-11-24 02:36:31 +01:00

404 lines
7.8 KiB
C

/*
* BIRD Resource Manager -- A SLAB-like Memory Allocator
*
* Heavily inspired by the original SLAB paper by Jeff Bonwick.
*
* (c) 1998--2000 Martin Mares <mj@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
/**
* DOC: Slabs
*
* Slabs are collections of memory blocks of a fixed size.
* They support very fast allocation and freeing of such blocks, prevent memory
* fragmentation and optimize L2 cache usage. Slabs have been invented by Jeff Bonwick
* and published in USENIX proceedings as `The Slab Allocator: An Object-Caching Kernel
* Memory Allocator'. Our implementation follows this article except that we don't use
* constructors and destructors.
*
* When the |DEBUGGING| switch is turned on, we automatically fill all
* newly allocated and freed blocks with a special pattern to make detection
* of use of uninitialized or already freed memory easier.
*
* Example: Nodes of a FIB are allocated from a per-FIB Slab.
*/
#include <stdlib.h>
#include <stdint.h>
#include "nest/bird.h"
#include "lib/resource.h"
#include "lib/string.h"
#undef FAKE_SLAB /* Turn on if you want to debug memory allocations */
#ifdef DEBUGGING
#define POISON /* Poison all regions after they are freed */
#endif
static void slab_free(resource *r);
static void slab_dump(resource *r);
static resource *slab_lookup(resource *r, unsigned long addr);
static size_t slab_memsize(resource *r);
#ifdef FAKE_SLAB
/*
* Fake version used for debugging.
*/
struct slab {
resource r;
uint size;
list objs;
};
static struct resclass sl_class = {
"FakeSlab",
sizeof(struct slab),
slab_free,
slab_dump,
NULL,
slab_memsize
};
struct sl_obj {
node n;
uintptr_t data_align[0];
byte data[0];
};
slab *
sl_new(pool *p, uint size)
{
slab *s = ralloc(p, &sl_class);
s->size = size;
init_list(&s->objs);
return s;
}
void *
sl_alloc(slab *s)
{
struct sl_obj *o = xmalloc(sizeof(struct sl_obj) + s->size);
add_tail(&s->objs, &o->n);
return o->data;
}
void *
sl_allocz(slab *s)
{
void *obj = sl_alloc(s);
memset(obj, 0, s->size);
return obj;
}
void
sl_free(slab *s, void *oo)
{
struct sl_obj *o = SKIP_BACK(struct sl_obj, data, oo);
rem_node(&o->n);
xfree(o);
}
static void
slab_free(resource *r)
{
slab *s = (slab *) r;
struct sl_obj *o, *p;
for(o = HEAD(s->objs); p = (struct sl_obj *) o->n.next; o = p)
xfree(o);
}
static void
slab_dump(resource *r)
{
slab *s = (slab *) r;
int cnt = 0;
struct sl_obj *o;
WALK_LIST(o, s->objs)
cnt++;
debug("(%d objects per %d bytes)\n", cnt, s->size);
}
static size_t
slab_memsize(resource *r)
{
slab *s = (slab *) r;
size_t cnt = 0;
struct sl_obj *o;
WALK_LIST(o, s->objs)
cnt++;
return ALLOC_OVERHEAD + sizeof(struct slab) + cnt * (ALLOC_OVERHEAD + s->size);
}
#else
/*
* Real efficient version.
*/
#define SLAB_SIZE 4096
#define MAX_EMPTY_HEADS 1
struct slab {
resource r;
uint obj_size, head_size, objs_per_slab, num_empty_heads, data_size;
list empty_heads, partial_heads, full_heads;
};
static struct resclass sl_class = {
"Slab",
sizeof(struct slab),
slab_free,
slab_dump,
slab_lookup,
slab_memsize
};
struct sl_head {
node n;
struct sl_obj *first_free;
int num_full;
};
struct sl_obj {
struct sl_head *slab;
union {
struct sl_obj *next;
byte data[0];
} u;
};
struct sl_alignment { /* Magic structure for testing of alignment */
byte data;
int x[0];
};
/**
* sl_new - create a new Slab
* @p: resource pool
* @size: block size
*
* This function creates a new Slab resource from which
* objects of size @size can be allocated.
*/
slab *
sl_new(pool *p, uint size)
{
slab *s = ralloc(p, &sl_class);
uint align = sizeof(struct sl_alignment);
if (align < sizeof(int))
align = sizeof(int);
s->data_size = size;
size += OFFSETOF(struct sl_obj, u.data);
if (size < sizeof(struct sl_obj))
size = sizeof(struct sl_obj);
size = (size + align - 1) / align * align;
s->obj_size = size;
s->head_size = (sizeof(struct sl_head) + align - 1) / align * align;
s->objs_per_slab = (SLAB_SIZE - s->head_size) / size;
if (!s->objs_per_slab)
bug("Slab: object too large");
s->num_empty_heads = 0;
init_list(&s->empty_heads);
init_list(&s->partial_heads);
init_list(&s->full_heads);
return s;
}
static struct sl_head *
sl_new_head(slab *s)
{
struct sl_head *h = xmalloc(SLAB_SIZE);
struct sl_obj *o = (struct sl_obj *)((byte *)h+s->head_size);
struct sl_obj *no;
uint n = s->objs_per_slab;
*h = (struct sl_head) {
.first_free = o,
.num_full = 0,
};
while (n--)
{
o->slab = h;
no = (struct sl_obj *)((char *) o+s->obj_size);
o->u.next = n ? no : NULL;
o = no;
}
return h;
}
/**
* sl_alloc - allocate an object from Slab
* @s: slab
*
* sl_alloc() allocates space for a single object from the
* Slab and returns a pointer to the object.
*/
void *
sl_alloc(slab *s)
{
struct sl_head *h;
struct sl_obj *o;
redo:
h = HEAD(s->partial_heads);
if (!h->n.next)
goto no_partial;
okay:
o = h->first_free;
if (!o)
goto full_partial;
h->first_free = o->u.next;
h->num_full++;
#ifdef POISON
memset(o->u.data, 0xcd, s->data_size);
#endif
return o->u.data;
full_partial:
rem_node(&h->n);
add_tail(&s->full_heads, &h->n);
goto redo;
no_partial:
h = HEAD(s->empty_heads);
if (h->n.next)
{
rem_node(&h->n);
add_head(&s->partial_heads, &h->n);
s->num_empty_heads--;
goto okay;
}
h = sl_new_head(s);
add_head(&s->partial_heads, &h->n);
goto okay;
}
/**
* sl_allocz - allocate an object from Slab and zero it
* @s: slab
*
* sl_allocz() allocates space for a single object from the
* Slab and returns a pointer to the object after zeroing out
* the object memory.
*/
void *
sl_allocz(slab *s)
{
void *obj = sl_alloc(s);
memset(obj, 0, s->data_size);
return obj;
}
/**
* sl_free - return a free object back to a Slab
* @s: slab
* @oo: object returned by sl_alloc()
*
* This function frees memory associated with the object @oo
* and returns it back to the Slab @s.
*/
void
sl_free(slab *s, void *oo)
{
struct sl_obj *o = SKIP_BACK(struct sl_obj, u.data, oo);
struct sl_head *h = o->slab;
#ifdef POISON
memset(oo, 0xdb, s->data_size);
#endif
o->u.next = h->first_free;
h->first_free = o;
if (!--h->num_full)
{
rem_node(&h->n);
if (s->num_empty_heads >= MAX_EMPTY_HEADS)
xfree(h);
else
{
add_head(&s->empty_heads, &h->n);
s->num_empty_heads++;
}
}
else if (!o->u.next)
{
rem_node(&h->n);
add_head(&s->partial_heads, &h->n);
}
}
static void
slab_free(resource *r)
{
slab *s = (slab *) r;
struct sl_head *h, *g;
WALK_LIST_DELSAFE(h, g, s->empty_heads)
xfree(h);
WALK_LIST_DELSAFE(h, g, s->partial_heads)
xfree(h);
WALK_LIST_DELSAFE(h, g, s->full_heads)
xfree(h);
}
static void
slab_dump(resource *r)
{
slab *s = (slab *) r;
int ec=0, pc=0, fc=0;
struct sl_head *h;
WALK_LIST(h, s->empty_heads)
ec++;
WALK_LIST(h, s->partial_heads)
pc++;
WALK_LIST(h, s->full_heads)
fc++;
debug("(%de+%dp+%df blocks per %d objs per %d bytes)\n", ec, pc, fc, s->objs_per_slab, s->obj_size);
}
static size_t
slab_memsize(resource *r)
{
slab *s = (slab *) r;
size_t heads = 0;
struct sl_head *h;
WALK_LIST(h, s->empty_heads)
heads++;
WALK_LIST(h, s->partial_heads)
heads++;
WALK_LIST(h, s->full_heads)
heads++;
return ALLOC_OVERHEAD + sizeof(struct slab) + heads * (ALLOC_OVERHEAD + SLAB_SIZE);
}
static resource *
slab_lookup(resource *r, unsigned long a)
{
slab *s = (slab *) r;
struct sl_head *h;
WALK_LIST(h, s->partial_heads)
if ((unsigned long) h < a && (unsigned long) h + SLAB_SIZE < a)
return r;
WALK_LIST(h, s->full_heads)
if ((unsigned long) h < a && (unsigned long) h + SLAB_SIZE < a)
return r;
return NULL;
}
#endif