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Cache freed VM stack pages instead of freeing them immediately #23470

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f37a994
Cache freed VM stack pages instead of freeing them immediately
ondrejmirtes Aug 16, 2026
c675c1d
Initialize vm_stack_page_cache, vm_stack_page_cache_count
arnaud-lb Aug 26, 2026
d15d831
Use a separate cache for fibers
arnaud-lb Aug 26, 2026
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25 changes: 25 additions & 0 deletions Zend/zend_execute.c
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Original file line number Diff line number Diff line change
Expand Up @@ -191,6 +191,10 @@ ZEND_API const zend_internal_function zend_pass_function = {
ZEND_API void zend_vm_stack_init(void)
{
EG(vm_stack_page_size) = ZEND_VM_STACK_PAGE_SIZE;
EG(vm_stack_page_cache) = NULL;
EG(vm_stack_page_cache_count) = 0;
EG(fiber_vm_stack_page_cache) = NULL;
EG(fiber_vm_stack_page_cache_count) = 0;
EG(vm_stack) = zend_vm_stack_new_page(ZEND_VM_STACK_PAGE_SIZE, NULL);
EG(vm_stack_top) = EG(vm_stack)->top;
EG(vm_stack_end) = EG(vm_stack)->end;
Expand All @@ -201,6 +205,10 @@ ZEND_API void zend_vm_stack_init_ex(size_t page_size)
/* page_size must be a power of 2 */
ZEND_ASSERT(page_size > 0 && (page_size & (page_size - 1)) == 0);
EG(vm_stack_page_size) = page_size;
EG(vm_stack_page_cache) = NULL;
EG(vm_stack_page_cache_count) = 0;
EG(fiber_vm_stack_page_cache) = NULL;
EG(fiber_vm_stack_page_cache_count) = 0;
EG(vm_stack) = zend_vm_stack_new_page(page_size, NULL);
EG(vm_stack_top) = EG(vm_stack)->top;
EG(vm_stack_end) = EG(vm_stack)->end;
Expand All @@ -217,6 +225,23 @@ ZEND_API void zend_vm_stack_destroy(void)
}
}

ZEND_API void zend_vm_stack_destroy_caches(void)
{
while (EG(vm_stack_page_cache) != NULL) {
zend_vm_stack cached = EG(vm_stack_page_cache);
EG(vm_stack_page_cache) = cached->prev;
efree(cached);
}
EG(vm_stack_page_cache_count) = 0;

while (EG(fiber_vm_stack_page_cache) != NULL) {
zend_vm_stack cached = EG(fiber_vm_stack_page_cache);
EG(fiber_vm_stack_page_cache) = cached->prev;
efree(cached);
}
EG(fiber_vm_stack_page_cache_count) = 0;
}

ZEND_API void* zend_vm_stack_extend(size_t size)
{
zend_vm_stack stack;
Expand Down
52 changes: 50 additions & 2 deletions Zend/zend_execute.h
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Expand Up @@ -322,10 +322,41 @@ ZEND_STATIC_ASSERT(ZEND_MM_ALIGNED_SIZE(sizeof(zval)) == sizeof(zval),
ZEND_API void zend_vm_stack_init(void);
ZEND_API void zend_vm_stack_init_ex(size_t page_size);
ZEND_API void zend_vm_stack_destroy(void);
ZEND_API void zend_vm_stack_destroy_caches(void);
ZEND_API void* zend_vm_stack_extend(size_t size);

#define ZEND_FIBER_VM_STACK_SIZE (1024 * sizeof(zval))

static zend_always_inline zend_vm_stack zend_vm_stack_cached_page(size_t size) {
zend_vm_stack page;

if (size == ZEND_FIBER_VM_STACK_SIZE) {
page = EG(fiber_vm_stack_page_cache);
if (page) {
ZEND_ASSERT((size_t)((char*)page->end - (char*)page) == size);
EG(fiber_vm_stack_page_cache) = page->prev;
EG(fiber_vm_stack_page_cache_count)--;
return page;
}
} else {
page = EG(vm_stack_page_cache);
ZEND_ASSERT(!page || ((size_t)((char*)page->end - (char*)page) == size) || size != EG(vm_stack_page_size));
if (page && EXPECTED((size_t)((char*)page->end - (char*)page) == size)) {
EG(vm_stack_page_cache) = page->prev;
EG(vm_stack_page_cache_count)--;
return page;
}
}

return NULL;
}

static zend_always_inline zend_vm_stack zend_vm_stack_new_page(size_t size, zend_vm_stack prev) {
zend_vm_stack page = (zend_vm_stack)emalloc(size);
zend_vm_stack page = zend_vm_stack_cached_page(size);

if (!page) {
page = (zend_vm_stack)emalloc(size);
}

page->top = ZEND_VM_STACK_ELEMENTS(page);
page->end = (zval*)((char*)page + size);
Expand Down Expand Up @@ -421,7 +452,24 @@ static zend_always_inline void zend_vm_stack_free_call_frame_ex(uint32_t call_in
EG(vm_stack_top) = prev->top;
EG(vm_stack_end) = prev->end;
EG(vm_stack) = prev;
efree(p);
if ((size_t)((char*)p->end - (char*)p) == ZEND_FIBER_VM_STACK_SIZE) {
if (EG(fiber_vm_stack_page_cache_count) < 32) {
p->prev = EG(fiber_vm_stack_page_cache);
EG(fiber_vm_stack_page_cache) = p;
EG(fiber_vm_stack_page_cache_count)++;
} else {
efree(p);
}
} else {
if (EG(vm_stack_page_cache_count) < 32
&& (size_t)((char*)p->end - (char*)p) == EG(vm_stack_page_size)) {
p->prev = EG(vm_stack_page_cache);
EG(vm_stack_page_cache) = p;
EG(vm_stack_page_cache_count)++;
} else {
efree(p);
}
}
} else {
EG(vm_stack_top) = (zval*)call;
}
Expand Down
1 change: 1 addition & 0 deletions Zend/zend_execute_API.c
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Original file line number Diff line number Diff line change
Expand Up @@ -482,6 +482,7 @@ void shutdown_executor(void) /* {{{ */
zend_hash_discard(EG(class_table), EG(persistent_classes_count));
} else {
zend_vm_stack_destroy();
zend_vm_stack_destroy_caches();

if (EG(full_tables_cleanup)) {
zend_hash_reverse_apply(EG(function_table), clean_non_persistent_function_full);
Expand Down
1 change: 0 additions & 1 deletion Zend/zend_fibers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,6 @@
#define ZEND_FIBER_GUARD_PAGES 1

#define ZEND_FIBER_DEFAULT_C_STACK_SIZE (4096 * (((sizeof(void *)) < 8) ? 256 : 512))
#define ZEND_FIBER_VM_STACK_SIZE (1024 * sizeof(zval))

BEGIN_EXTERN_C()

Expand Down
5 changes: 5 additions & 0 deletions Zend/zend_globals.h
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Original file line number Diff line number Diff line change
Expand Up @@ -202,6 +202,11 @@ struct _zend_executor_globals {
zval *vm_stack_end;
zend_vm_stack vm_stack;
size_t vm_stack_page_size;
zend_vm_stack vm_stack_page_cache;
uint32_t vm_stack_page_cache_count;
/* Fibers use a different page size, so they need a separate cache */
zend_vm_stack fiber_vm_stack_page_cache;
uint32_t fiber_vm_stack_page_cache_count;

struct _zend_execute_data *current_execute_data;
const zend_class_entry *fake_scope; /* used to avoid checks accessing properties */
Expand Down
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