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[wasm] Add custom mmap/munmap implementation for anonymous mappings #101871

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May 10, 2024
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8 changes: 6 additions & 2 deletions src/mono/mono/sgen/sgen-internal.c
Original file line number Diff line number Diff line change
Expand Up @@ -273,7 +273,7 @@ sgen_report_internal_mem_usage (void)
void
sgen_init_internal_allocator (void)
{
int i, size;
int i;

for (i = 0; i < INTERNAL_MEM_MAX; ++i)
fixed_type_allocator_indexes [i] = -1;
Expand All @@ -284,7 +284,10 @@ sgen_init_internal_allocator (void)
mono_lock_free_allocator_init_allocator (&allocators [i], &size_classes [i], MONO_MEM_ACCOUNT_SGEN_INTERNAL);
}

for (size = mono_pagesize (); size <= LOCK_FREE_ALLOC_SB_MAX_SIZE; size <<= 1) {
// FIXME: This whole algorithm is broken on WASM due to its 64KB page size.
// Previously SB_MAX_SIZE was < mono_pagesize, so none of this ran.
#ifndef HOST_WASM
for (int size = mono_pagesize (); size <= LOCK_FREE_ALLOC_SB_MAX_SIZE; size <<= 1) {
int max_size = (LOCK_FREE_ALLOC_SB_USABLE_SIZE (size) / 2) & ~(SIZEOF_VOID_P - 1);
/*
* we assert that allocator_sizes contains the biggest possible object size
Expand All @@ -297,6 +300,7 @@ sgen_init_internal_allocator (void)
if (size < LOCK_FREE_ALLOC_SB_MAX_SIZE)
g_assert (block_size (max_size + 1) == size << 1);
}
#endif
}

#endif
6 changes: 5 additions & 1 deletion src/mono/mono/sgen/sgen-marksweep.c
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include "mono/sgen/sgen-client.h"
#include "mono/utils/mono-memory-model.h"
#include "mono/utils/mono-proclib.h"
#include "mono/utils/options.h"

static int ms_block_size;

Expand Down Expand Up @@ -2133,12 +2134,15 @@ major_free_swept_blocks (size_t section_reserve)
{
SGEN_ASSERT (0, sweep_state == SWEEP_STATE_SWEPT, "Sweeping must have finished before freeing blocks");

#if defined(HOST_WIN32) || defined(HOST_ORBIS) || defined (HOST_WASM)
#if defined(HOST_WIN32) || defined(HOST_ORBIS)
/*
* sgen_free_os_memory () asserts in mono_vfree () because windows doesn't like freeing the middle of
* a VirtualAlloc ()-ed block.
*/
return;
#elif defined(HOST_WASM)
if (!mono_opt_wasm_mmap)
return;
#endif

{
Expand Down
2 changes: 1 addition & 1 deletion src/mono/mono/utils/CMakeLists.txt
Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,7 @@ set(utils_arch_sources "${utils_arch_sources};mono-hwcap-riscv.c")
elseif(TARGET_S390X)
set(utils_arch_sources "${utils_arch_sources};mono-hwcap-s390x.c")
elseif(TARGET_WASM)
set(utils_arch_sources "${utils_arch_sources};mono-hwcap-wasm.c;mono-mmap-wasm.c")
set(utils_arch_sources "${utils_arch_sources};mono-hwcap-wasm.c;mono-mmap-wasm.c;mono-wasm-pagemgr.c")
elseif(TARGET_WASI)
set(utils_arch_sources "${utils_arch_sources};mono-hwcap-wasm.c")
elseif(TARGET_POWERPC OR TARGET_POWERPC64)
Expand Down
1 change: 1 addition & 0 deletions src/mono/mono/utils/lock-free-alloc.h
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,7 @@ typedef struct {
MonoMemAccountType account_type;
} MonoLockFreeAllocator;

// FIXME: On WASM the page size is 64KB, so this isn't enough.
#define LOCK_FREE_ALLOC_SB_MAX_SIZE 16384
#define LOCK_FREE_ALLOC_SB_HEADER_SIZE (sizeof (gpointer))
#define LOCK_FREE_ALLOC_SB_USABLE_SIZE(block_size) ((block_size) - LOCK_FREE_ALLOC_SB_HEADER_SIZE)
Expand Down
34 changes: 31 additions & 3 deletions src/mono/mono/utils/mono-mmap-wasm.c
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,9 @@
#include "mono-proclib.h"
#include <mono/utils/mono-threads.h>
#include <mono/utils/atomic.h>
#include <mono/utils/options.h>

#include "mono-wasm-pagemgr.h"

#define BEGIN_CRITICAL_SECTION do { \
MonoThreadInfo *__info = mono_thread_info_current_unchecked (); \
Expand All @@ -34,6 +37,9 @@
int
mono_pagesize (void)
{
if (mono_opt_wasm_mmap)
return MWPM_PAGE_SIZE;

static int saved_pagesize = 0;

if (saved_pagesize)
Expand Down Expand Up @@ -108,7 +114,16 @@ valloc_impl (void *addr, size_t size, int flags, MonoMemAccountType type)
mflags |= MAP_PRIVATE;

BEGIN_CRITICAL_SECTION;
ptr = mmap (addr, size, prot, mflags, -1, 0);
if (mono_opt_wasm_mmap) {
// FIXME: Make this work if the requested address range is free
if ((flags & MONO_MMAP_FIXED) && addr)
return NULL;

ptr = mwpm_alloc_range (size, 1);
if (!ptr)
return NULL;
} else
ptr = mmap (addr, size, prot, mflags, -1, 0);
END_CRITICAL_SECTION;

if (ptr == MAP_FAILED)
Expand Down Expand Up @@ -142,6 +157,10 @@ typedef struct {
void*
mono_valloc_aligned (size_t size, size_t alignment, int flags, MonoMemAccountType type)
{
// We don't need padding if the alignment is compatible with the page size
if (mono_opt_wasm_mmap && ((MWPM_PAGE_SIZE % alignment) == 0))
return valloc_impl (NULL, size, flags, type);

/* Allocate twice the memory to be able to put the block on an aligned address */
char *mem = (char *) valloc_impl (NULL, size + alignment, flags, type);
char *aligned;
Expand Down Expand Up @@ -175,13 +194,22 @@ mono_vfree (void *addr, size_t length, MonoMemAccountType type)
* mono_valloc_align (), free the original mapping.
*/
BEGIN_CRITICAL_SECTION;
munmap (info->addr, info->size);
if (mono_opt_wasm_mmap)
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mwpm_free_range (info->addr, info->size);
else
munmap (info->addr, info->size);
END_CRITICAL_SECTION;
g_free (info);
g_hash_table_remove (valloc_hash, addr);
} else {
// FIXME: We could be trying to unmap part of an aligned mapping, in which case the
// hash lookup failed because addr isn't exactly the start of the mapping.
// Ideally if the custom page manager is enabled, we won't have done aligned alloc.
BEGIN_CRITICAL_SECTION;
munmap (addr, length);
if (mono_opt_wasm_mmap)
mwpm_free_range (addr, length);
else
munmap (addr, length);
END_CRITICAL_SECTION;
}

Expand Down
3 changes: 2 additions & 1 deletion src/mono/mono/utils/mono-mmap.h
Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,8 @@ enum {
MONO_MMAP_ANON = 1 << 6,
MONO_MMAP_FIXED = 1 << 7,
MONO_MMAP_32BIT = 1 << 8,
MONO_MMAP_JIT = 1 << 9
MONO_MMAP_JIT = 1 << 9,
MONO_MMAP_NOZERO = 1 << 10,
};

typedef enum {
Expand Down
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