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Keeping un-unmmappable pages until they can be reused

Browse Source 
On Linux, munmap() may fail with ENOMEM when virtual memory is too
fragmented. Working this around by just keeping such blocks for future
use.
This commit is contained in:
Maria Matejka 2021-11-11 16:25:59 +01:00
parent 4f3fa1623f
commit 794a4eefa1
3 changed files with 59 additions and 8 deletions
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1
lib/locking.h
View File

@ -19,6 +19,7 @@ struct lock_order {
struct domain_generic *attrs;
struct domain_generic *cork;
struct domain_generic *event;
struct domain_generic *resource;
};
extern _Thread_local struct lock_order locking_stack;

23
lib/resource.c
View File

@ -60,7 +60,7 @@ static struct resclass pool_class = {
pool root_pool;
void *alloc_sys_page(void);
void free_sys_page(void *);
int free_sys_page(void *);
static int indent;
@ -98,8 +98,10 @@ pool_free(resource *P)
if (p->pages)
{
ASSERT_DIE(!p->pages->used);
for (uint i=0; i<p->pages->free; i++)
for (uint i = 0; i < p->pages->free; i++)
free_sys_page(p->pages->ptr[i]);
free_sys_page(p->pages);
}
}
@ -476,10 +478,19 @@ free_page(pool *p, void *ptr)
ASSERT_DIE(p->pages);
p->pages->used--;
if (p->pages->free >= POOL_PAGES_MAX)
return free_sys_page(ptr);
else
p->pages->ptr[p->pages->free++] = ptr;
ASSERT_DIE(p->pages->free <= POOL_PAGES_MAX);
if (p->pages->free == POOL_PAGES_MAX)
{
const unsigned long keep = POOL_PAGES_MAX / 4;
for (uint i = keep; i < p->pages->free; i++)
free_sys_page(p->pages->ptr[i]);
p->pages->free = keep;
}
p->pages->ptr[p->pages->free++] = ptr;
}

43
sysdep/unix/alloc.c
View File

@ -11,6 +11,8 @@
#include <stdlib.h>
#include <unistd.h>
#include <stdatomic.h>
#include <errno.h>
#ifdef HAVE_MMAP
#include <sys/mman.h>
@ -19,6 +21,13 @@
long page_size = 0;
_Bool alloc_multipage = 0;
static _Atomic int global_page_list_not_empty;
static list global_page_list;
static _Atomic int global_page_spinlock;
#define GLOBAL_PAGE_SPIN_LOCK for (int v = 0; !atomic_compare_exchange_weak_explicit(&global_page_spinlock, &v, 1, memory_order_acq_rel, memory_order_acquire); v = 0)
#define GLOBAL_PAGE_SPIN_UNLOCK do { int v = 1; ASSERT_DIE(atomic_compare_exchange_strong_explicit(&global_page_spinlock, &v, 0, memory_order_acq_rel, memory_order_acquire)); } while (0)
#ifdef HAVE_MMAP
static _Bool use_fake = 0;
#else
@ -28,12 +37,14 @@ static _Bool use_fake = 1;
void resource_sys_init(void)
{
#ifdef HAVE_MMAP
init_list(&global_page_list);
if (!(page_size = sysconf(_SC_PAGESIZE)))
die("System page size must be non-zero");
if ((u64_popcount(page_size) > 1) || (page_size > 16384))
{
#endif
{
/* Too big or strange page, use the aligned allocator instead */
page_size = 4096;
use_fake = 1;
@ -46,6 +57,22 @@ alloc_sys_page(void)
#ifdef HAVE_MMAP
if (!use_fake)
{
if (atomic_load_explicit(&global_page_list_not_empty, memory_order_relaxed))
{
GLOBAL_PAGE_SPIN_LOCK;
if (!EMPTY_LIST(global_page_list))
{
node *ret = HEAD(global_page_list);
rem_node(ret);
if (EMPTY_LIST(global_page_list))
atomic_store_explicit(&global_page_list_not_empty, 0, memory_order_relaxed);
GLOBAL_PAGE_SPIN_UNLOCK;
memset(ret, 0, sizeof(node));
return (void *) ret;
}
GLOBAL_PAGE_SPIN_UNLOCK;
}
if (alloc_multipage)
{
void *big = mmap(NULL, page_size * 2, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@ -90,7 +117,19 @@ free_sys_page(void *ptr)
if (!use_fake)
{
if (munmap(ptr, page_size) < 0)
bug("munmap(%p) failed: %m", ptr);
#ifdef ENOMEM
if (errno == ENOMEM)
{
memset(ptr, 0, page_size);
GLOBAL_PAGE_SPIN_LOCK;
add_tail(&global_page_list, (node *) ptr);
atomic_store_explicit(&global_page_list_not_empty, 1, memory_order_relaxed);
GLOBAL_PAGE_SPIN_UNLOCK;
}
else
#endif
bug("munmap(%p) failed: %m", ptr);
}
else
#endif