bird/sysdep/unix/alloc.c
Maria Matejka 9eec503b25 Fixed a munmap abort bug
When BIRD was munmapping too many pages, it sometimes aborted, saying
that munmap failed with "Not enough memory" as the address space was
getting more and more fragmented.

There is a workaround in place, simply keeping that page for future use,
yet it has never been compiled in because I somehow forgot to include
errno.h. And because I also thought that somebody may have ENOMEM not
defined (why?!), there was a check which quietly omitted that
workaround.

Anyway, ENOMEM is POSIX. It's an utter nonsense to check for its
existence. If it doesn't exist, something is broken.
2022-04-13 11:36:54 +02:00

187 lines
3.6 KiB
C

/*
* 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 <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_MAIN_MAX 256
#define KEEP_PAGES_MAIN_MIN 8
#define CLEANUP_PAGES_BULK 256
STATIC_ASSERT(KEEP_PAGES_MAIN_MIN * 4 < KEEP_PAGES_MAIN_MAX);
static _Bool use_fake = 0;
#if DEBUGGING
struct free_page {
node unused[42];
node n;
};
#else
struct free_page {
node n;
};
#endif
struct free_pages {
list pages;
u16 min, max; /* Minimal and maximal number of free pages kept */
uint cnt; /* Number of empty pages */
event cleanup;
};
static void global_free_pages_cleanup_event(void *);
static struct free_pages global_free_pages = {
.min = KEEP_PAGES_MAIN_MIN,
.max = KEEP_PAGES_MAIN_MAX,
.cleanup = { .hook = global_free_pages_cleanup_event },
};
uint *pages_kept = &global_free_pages.cnt;
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
struct free_pages *fps = &global_free_pages;
if (fps->cnt)
{
struct free_page *fp = SKIP_BACK(struct free_page, n, HEAD(fps->pages));
rem_node(&fp->n);
if ((--fps->cnt < fps->min) && !shutting_down)
ev_schedule(&fps->cleanup);
bzero(fp, page_size);
return fp;
}
return alloc_sys_page();
#endif
}
void
free_page(void *ptr)
{
if (use_fake)
{
free(ptr);
return;
}
#ifdef HAVE_MMAP
struct free_pages *fps = &global_free_pages;
struct free_page *fp = ptr;
fp->n = (node) {};
add_tail(&fps->pages, &fp->n);
if ((++fps->cnt > fps->max) && !shutting_down)
ev_schedule(&fps->cleanup);
#endif
}
#ifdef HAVE_MMAP
static void
global_free_pages_cleanup_event(void *data UNUSED)
{
if (shutting_down)
return;
struct free_pages *fps = &global_free_pages;
while (fps->cnt / 2 < fps->min)
{
struct free_page *fp = alloc_sys_page();
fp->n = (node) {};
add_tail(&fps->pages, &fp->n);
fps->cnt++;
}
for (uint seen = 0; (seen < CLEANUP_PAGES_BULK) && (fps->cnt > fps->max / 2); seen++)
{
struct free_page *fp = SKIP_BACK(struct free_page, n, TAIL(fps->pages));
rem_node(&fp->n);
if (munmap(fp, page_size) == 0)
fps->cnt--;
else if (errno == ENOMEM)
add_head(&fps->pages, &fp->n);
else
bug("munmap(%p) failed: %m", fp);
}
}
#endif
void
resource_sys_init(void)
{
#ifdef HAVE_MMAP
ASSERT_DIE(global_free_pages.cnt == 0);
if (!(page_size = sysconf(_SC_PAGESIZE)))
die("System page size must be non-zero");
if (u64_popcount(page_size) == 1)
{
struct free_pages *fps = &global_free_pages;
init_list(&fps->pages);
global_free_pages_cleanup_event(NULL);
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;
}