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/*
* BIRD Internet Routing Daemon -- Raw allocation
*
* (c) 2020 Maria Matejka <mq@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
#include "nest/bird.h"
#include "lib/resource.h"
#include "lib/lists.h"
#include "lib/event.h"
#include "lib/rcu.h"
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif
long page_size = 0;
#ifdef HAVE_MMAP
#define KEEP_PAGES_MAX 256
#define KEEP_PAGES_MIN 8
STATIC_ASSERT(KEEP_PAGES_MIN * 4 < KEEP_PAGES_MAX);
static _Bool use_fake = 0;
static _Bool initialized = 0;
#if DEBUGGING
struct free_page {
node unused[42];
struct free_page * _Atomic next;
};
#else
struct free_page {
struct free_page * _Atomic next;
};
#endif
static struct free_page * _Atomic page_stack = NULL;
static void page_cleanup(void *);
static event page_cleanup_event = { .hook = page_cleanup, };
#define SCHEDULE_CLEANUP do if (initialized && !shutting_down) ev_send(&global_event_list, &page_cleanup_event); while (0)
_Atomic int pages_kept = 0;
static void *
alloc_sys_page(void)
{
void *ptr = mmap(NULL, page_size, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (ptr == MAP_FAILED)
bug("mmap(%lu) failed: %m", page_size);
return ptr;
}
extern int shutting_down; /* Shutdown requested. */
#else // ! HAVE_MMAP
#define use_fake 1
#endif
void *
alloc_page(void)
{
if (use_fake)
{
void *ptr = NULL;
int err = posix_memalign(&ptr, page_size, page_size);
if (err || !ptr)
bug("posix_memalign(%lu) failed", (long unsigned int) page_size);
return ptr;
}
#ifdef HAVE_MMAP
rcu_read_lock();
struct free_page *fp = atomic_load_explicit(&page_stack, memory_order_acquire);
while (fp && !atomic_compare_exchange_strong_explicit(
&page_stack, &fp, atomic_load_explicit(&fp->next, memory_order_acquire),
memory_order_acq_rel, memory_order_acquire))
;
rcu_read_unlock();
if (!fp)
return alloc_sys_page();
if (atomic_fetch_sub_explicit(&pages_kept, 1, memory_order_relaxed) <= KEEP_PAGES_MIN)
SCHEDULE_CLEANUP;
return fp;
#endif
}
void
free_page(void *ptr)
{
if (use_fake)
{
free(ptr);
return;
}
#ifdef HAVE_MMAP
rcu_read_lock();
struct free_page *fp = ptr;
struct free_page *next = atomic_load_explicit(&page_stack, memory_order_acquire);
do atomic_store_explicit(&fp->next, next, memory_order_release);
while (!atomic_compare_exchange_strong_explicit(
&page_stack, &next, fp,
memory_order_acq_rel, memory_order_acquire));
rcu_read_unlock();
if (atomic_fetch_add_explicit(&pages_kept, 1, memory_order_relaxed) >= KEEP_PAGES_MAX)
SCHEDULE_CLEANUP;
#endif
}
#ifdef HAVE_MMAP
static void
page_cleanup(void *_ UNUSED)
{
struct free_page *stack = atomic_exchange_explicit(&page_stack, NULL, memory_order_acq_rel);
if (!stack)
return;
synchronize_rcu();
do {
struct free_page *f = stack;
stack = atomic_load_explicit(&f->next, memory_order_acquire);
if (munmap(f, page_size) == 0)
continue;
else if (errno != ENOMEM)
bug("munmap(%p) failed: %m", f);
else
free_page(f);
}
while (stack && (atomic_fetch_sub_explicit(&pages_kept, 1, memory_order_relaxed) >= KEEP_PAGES_MAX / 2));
while (stack)
{
atomic_fetch_sub_explicit(&pages_kept, 1, memory_order_relaxed);
struct free_page *f = stack;
stack = atomic_load_explicit(&f->next, memory_order_acquire);
free_page(f);
}
}
#endif
void
resource_sys_init(void)
{
#ifdef HAVE_MMAP
if (!(page_size = sysconf(_SC_PAGESIZE)))
die("System page size must be non-zero");
if (u64_popcount(page_size) == 1)
{
for (int i = 0; i < (KEEP_PAGES_MIN * 2); i++)
free_page(alloc_page());
page_cleanup(NULL);
initialized = 1;
return;
}
/* Too big or strange page, use the aligned allocator instead */
log(L_WARN "Got strange memory page size (%lu), using the aligned allocator instead", page_size);
use_fake = 1;
#endif
page_size = 4096;
initialized = 1;
}
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