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Mono: increase default stack size on s390x/ppc64le; support DOTNET_Thread_DefaultStackSize for setting stack size. #124588

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Merged
akoeplinger merged 5 commits into from
Feb 25, 2026
Merged

Mono: increase default stack size on s390x/ppc64le; support DOTNET_Thread_DefaultStackSize for setting stack size. #124588

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0dd5dcd
mono-threads-posix: use 8MB stack by default on s390x/ppc64le. Enable…
tmds Feb 23, 2026
92d5576
Support DOTNET_Thread_DefaultStackSize also on Windows.
tmds Feb 24, 2026
d4e8d7e
Fix build.
tmds Feb 24, 2026
7c3fa34
Update src/mono/mono/metadata/threads.c
tmds Feb 24, 2026
3867b51
Sync mono-threads-wasm with mono-threads-posix.
tmds Feb 24, 2026
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13 changes: 13 additions & 0 deletions src/mono/CMakeLists.txt
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Expand Up @@ -496,6 +496,19 @@ else()
message(FATAL_ERROR "TARGET_ARCH='${TARGET_ARCH}' not supported.")
endif()

# Default stack size: 2MB for 64-bit, 1MB for 32-bit.
# Use large (8MB) stack size for s390x/ppc64le due to limited tail call optimization support.
# On Windows, use 0 to defer to the OS/PE header default.
if(TARGET_WIN32)
set(MONO_DEFAULT_STACKSIZE 0)
elseif(TARGET_S390X OR TARGET_POWERPC64)
set(MONO_DEFAULT_STACKSIZE 8388608)
elseif(TARGET_SIZEOF_VOID_P EQUAL 4)
set(MONO_DEFAULT_STACKSIZE 1048576)
else()
set(MONO_DEFAULT_STACKSIZE 2097152)
endif()

# arm64 MacCatalyst runtime host or AOT target is more like Apple mobile targets than x64
if ((HOST_MACCAT AND HOST_ARM64) OR (TARGET_MACCAT AND TARGET_ARM64))
set(TARGET_APPLE_MOBILE 1)
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3 changes: 3 additions & 0 deletions src/mono/cmake/config.h.in
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Expand Up @@ -598,6 +598,9 @@
/* byte order of target */
#define TARGET_BYTE_ORDER @TARGET_BYTE_ORDER@

/* default stack size for managed threads */
#define MONO_DEFAULT_STACKSIZE @MONO_DEFAULT_STACKSIZE@

/* wordsize of target */
#define TARGET_SIZEOF_VOID_P @TARGET_SIZEOF_VOID_P@

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19 changes: 17 additions & 2 deletions src/mono/mono/metadata/threads.c
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Expand Up @@ -204,7 +204,7 @@ static MonoThreadAttachCB mono_thread_attach_cb = NULL;
static MonoThreadCleanupFunc mono_thread_cleanup_fn = NULL;

/* The default stack size for each thread */
static guint32 default_stacksize = 0;
static guint32 default_stacksize = ~0;

static void mono_free_static_data (gpointer* static_data);
static void mono_init_static_data_info (StaticDataInfo *static_data);
Expand Down Expand Up @@ -1371,7 +1371,7 @@ create_thread (MonoThread *thread, MonoInternalThread *internal, MonoThreadStart
mono_coop_sem_init (&start_info->registered, 0);

if (flags != MONO_THREAD_CREATE_FLAGS_SMALL_STACK)
stack_set_size = stack_size ? stack_size : default_stacksize;
stack_set_size = stack_size ? stack_size : mono_threads_get_default_stacksize();
else
stack_set_size = 0;

Expand Down Expand Up @@ -1445,6 +1445,21 @@ mono_threads_set_default_stacksize (guint32 stacksize)
guint32
mono_threads_get_default_stacksize (void)
{
if (default_stacksize == ~0)
{
unsigned long stacksize = 0;

const char *value = g_getenv ("DOTNET_Thread_DefaultStackSize");
if (value) {
errno = 0;
stacksize = strtoul (value, NULL, 16);
if (errno != 0 || stacksize >= UINT_MAX)
stacksize = 0;
}

default_stacksize = (guint32)stacksize;
}

return default_stacksize;
}

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6 changes: 3 additions & 3 deletions src/mono/mono/utils/mono-threads-posix.c
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Expand Up @@ -72,10 +72,10 @@ mono_thread_platform_create_thread (MonoThreadStart thread_fn, gpointer thread_d
if (RUNNING_ON_VALGRIND)
set_stack_size = 1 << 20;
else
set_stack_size = (SIZEOF_VOID_P / 4) * 1024 * 1024;
#else
set_stack_size = (SIZEOF_VOID_P / 4) * 1024 * 1024;
#endif
{
set_stack_size = MONO_DEFAULT_STACKSIZE;
}
}

#ifdef PTHREAD_STACK_MIN
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8 changes: 3 additions & 5 deletions src/mono/mono/utils/mono-threads-wasm.c
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Expand Up @@ -225,8 +225,6 @@ mono_thread_platform_create_thread (MonoThreadStart thread_fn, gpointer thread_d
g_error ("%s: pthread_attr_init failed, error: \"%s\" (%d)", __func__, g_strerror (res), res);

#if 0
gsize set_stack_size;

if (stack_size)
set_stack_size = *stack_size;
else
Expand All @@ -238,10 +236,10 @@ mono_thread_platform_create_thread (MonoThreadStart thread_fn, gpointer thread_d
if (RUNNING_ON_VALGRIND)
set_stack_size = 1 << 20;
else
set_stack_size = (SIZEOF_VOID_P / 4) * 1024 * 1024;
#else
set_stack_size = (SIZEOF_VOID_P / 4) * 1024 * 1024;
#endif
{
set_stack_size = MONO_DEFAULT_STACKSIZE;
}
}

#ifdef PTHREAD_STACK_MIN
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7 changes: 2 additions & 5 deletions src/mono/mono/utils/mono-threads-windows.c
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Expand Up @@ -395,15 +395,12 @@ mono_threads_suspend_get_abort_signal (void)

#if defined (HOST_WIN32)

// Use default stack size on netcore.
#define MONO_WIN32_DEFAULT_NATIVE_STACK_SIZE 0

gboolean
mono_thread_platform_create_thread (MonoThreadStart thread_fn, gpointer thread_data, gsize* const stack_size, MonoNativeThreadId *tid)
{
HANDLE result;
DWORD thread_id;
gsize set_stack_size = MONO_WIN32_DEFAULT_NATIVE_STACK_SIZE;
gsize set_stack_size = MONO_DEFAULT_STACKSIZE;

if (stack_size && *stack_size)
set_stack_size = *stack_size;
Expand Down Expand Up @@ -450,7 +447,7 @@ mono_native_thread_id_equals (MonoNativeThreadId id1, MonoNativeThreadId id2)
gboolean
mono_native_thread_create (MonoNativeThreadId *tid, gpointer func, gpointer arg)
{
return CreateThread (NULL, MONO_WIN32_DEFAULT_NATIVE_STACK_SIZE, (LPTHREAD_START_ROUTINE)func, arg, 0, tid) != NULL;
return CreateThread (NULL, MONO_DEFAULT_STACKSIZE, (LPTHREAD_START_ROUTINE)func, arg, 0, tid) != NULL;
}

gboolean
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