[wasm] stop using mmap/munmap (#108512)

Author: pavelsavara

src/mono/browser/browser.proj

@@ -209,6 +209,7 @@
       <EmccExportedFunction Include="_malloc" />
       <EmccExportedFunction Include="_sbrk" />
       <EmccExportedFunction Include="_memalign" />
+      <EmccExportedFunction Include="_posix_memalign" />
       <EmccExportedFunction Include="_memset" />
       <EmccExportedFunction Include="_ntohs" />
       <EmccExportedFunction Include="stackAlloc" />

src/mono/mono/sgen/sgen-los.c

@@ -334,7 +334,12 @@ get_los_section_memory (size_t size)
 	section->next = los_sections;
 	los_sections = section;
 
+#ifdef HOST_WASM
+	// on WASM there is no mmap and alignment has large overhead
+	sgen_los_memory_usage_total += LOS_SECTION_SIZE + LOS_SECTION_SIZE;
+#else
 	sgen_los_memory_usage_total += LOS_SECTION_SIZE;
+#endif
 	++los_num_sections;
 
 	goto retry;
@@ -542,7 +547,12 @@ sgen_los_sweep (void)
 			sgen_memgov_release_space (LOS_SECTION_SIZE, SPACE_LOS);
 			section = next;
 			--los_num_sections;
+#ifdef HOST_WASM
+			// on WASM there is no mmap and alignment has large overhead
+			sgen_los_memory_usage_total -= LOS_SECTION_SIZE + LOS_SECTION_SIZE;
+#else
 			sgen_los_memory_usage_total -= LOS_SECTION_SIZE;
+#endif
 			continue;
 		}
 

src/mono/mono/sgen/sgen-marksweep.c

@@ -49,7 +49,13 @@ static int ms_block_size;
  * Don't allocate single blocks, but alloc a contingent of this many
  * blocks in one swoop.  This must be a power of two.
  */
+#ifndef TARGET_WASM
 #define MS_BLOCK_ALLOC_NUM	32
+#else
+// WASM doesn't support partial munmap, so we can't free individual blocks
+// we use posix_memalign and free the whole block at once
+#define MS_BLOCK_ALLOC_NUM	1
+#endif
 
 #define MS_NUM_MARK_WORDS	((ms_block_size / SGEN_ALLOC_ALIGN + sizeof (guint32) * 8 - 1) / (sizeof (guint32) * 8))
 
@@ -2140,9 +2146,6 @@ major_free_swept_blocks (size_t section_reserve)
 		 * a VirtualAlloc ()-ed block.
 		 */
 		return;
-#elif defined(HOST_WASM)
-	if (!mono_opt_wasm_mmap)
-		return;
 #endif
 
 	{

src/mono/mono/utils/CMakeLists.txt

@@ -204,7 +204,7 @@ 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 "${utils_arch_sources};mono-hwcap-wasm.c;mono-mmap-wasm.c;mono-wasm-pagemgr.c")
+set(utils_arch_sources "${utils_arch_sources};mono-hwcap-wasm.c;mono-mmap-wasm.c")
 elseif(TARGET_WASI)
 set(utils_arch_sources "${utils_arch_sources};mono-hwcap-wasm.c")
 elseif(TARGET_POWERPC OR TARGET_POWERPC64)

src/mono/mono/utils/lock-free-alloc.h

@@ -46,7 +46,7 @@ typedef struct {
 } MonoLockFreeAllocator;
 
 #ifdef HOST_WASM
-#define LOCK_FREE_ALLOC_SB_MAX_SIZE					(mono_opt_wasm_mmap ? 65536 : 16384)
+#define LOCK_FREE_ALLOC_SB_MAX_SIZE					16384 * 32
 #else
 #define LOCK_FREE_ALLOC_SB_MAX_SIZE					16384
 #endif

src/mono/mono/utils/mono-mmap-wasm.c

@@ -24,8 +24,6 @@
 #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 (); \
 	if (__info) __info->inside_critical_region = TRUE;	\
@@ -37,22 +35,7 @@
 int
 mono_pagesize (void)
 {
-	if (mono_opt_wasm_mmap)
-		return MWPM_PAGE_SIZE;
-
-	static int saved_pagesize = 0;
-
-	if (saved_pagesize)
-		return saved_pagesize;
-
-	// Prefer sysconf () as it's signal safe.
-#if defined (HAVE_SYSCONF) && defined (_SC_PAGESIZE)
-	saved_pagesize = sysconf (_SC_PAGESIZE);
-#else
-	saved_pagesize = getpagesize ();
-#endif
-
-	return saved_pagesize;
+	return 16384;
 }
 
 int
@@ -96,122 +79,50 @@ mono_setmmapjit (int flag)
 	/* Ignored on HOST_WASM */
 }
 
-static void*
-valloc_impl (void *addr, size_t size, int flags, MonoMemAccountType type)
-{
-	void *ptr;
-	int mflags = 0;
-	int prot = prot_from_flags (flags);
-
-	if (!mono_valloc_can_alloc (size))
-		return NULL;
-
-	if (size == 0)
-		/* emscripten throws an exception on 0 length */
-		return NULL;
-
-	mflags |= MAP_ANONYMOUS;
-	mflags |= MAP_PRIVATE;
-
-	BEGIN_CRITICAL_SECTION;
-	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, (flags & MONO_MMAP_NOZERO) == 0);
-		if (!ptr)
-			return NULL;
-	} else
-		ptr = mmap (addr, size, prot, mflags, -1, 0);
-	END_CRITICAL_SECTION;
-
-	if (ptr == MAP_FAILED)
-		return NULL;
-
-	mono_account_mem (type, (ssize_t)size);
-
-	return ptr;
-}
 
 void*
-mono_valloc (void *addr, size_t size, int flags, MonoMemAccountType type)
+mono_valloc (void *addr, size_t length, int flags, MonoMemAccountType type)
 {
-#if HOST_WASI
-	// WASI implements mmap using malloc, so the returned address is not page aligned
-	// and our code depends on it
-	g_assert (!addr);
-	return mono_valloc_aligned (size, mono_pagesize (), flags, type);
-#else
-	return valloc_impl (addr, size, flags, type);
-#endif
+	g_assert (addr == NULL);
+	return mono_valloc_aligned (length, mono_pagesize (), flags, type);
 }
 
-static GHashTable *valloc_hash;
-
-typedef struct {
-	void *addr;
-	int size;
-} VallocInfo;
-
 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;
+#ifdef DISABLE_THREADS
+	void *old_sbrk = NULL;
+	if ((flags & MONO_MMAP_NOZERO) == 0) {
+		old_sbrk = sbrk (0);
+	}
+#endif
 
-	if (!mem)
+	void *res = NULL;
+	if (posix_memalign (&res, alignment, size))
 		return NULL;
 
-	aligned = mono_aligned_address (mem, size, alignment);
+#ifdef DISABLE_THREADS
+	if ((flags & MONO_MMAP_NOZERO) == 0 && old_sbrk > res) {
+		// this means that we got an old block, not the new block from sbrk
+		memset (res, 0, size);
+	}
+#else
+	if ((flags & MONO_MMAP_NOZERO) == 0) {
+		memset (res, 0, size);
+	}
+#endif
 
-	/* The mmap implementation in emscripten cannot unmap parts of regions */
-	/* Free the other two parts in when 'aligned' is freed */
-	// FIXME: This doubles the memory usage
-	if (!valloc_hash)
-		valloc_hash = g_hash_table_new (NULL, NULL);
-	VallocInfo *info = g_new0 (VallocInfo, 1);
-	info->addr = mem;
-	info->size = size + alignment;
-	g_hash_table_insert (valloc_hash, aligned, info);
+	mono_account_mem (type, (ssize_t)size);
 
-	return aligned;
+	return res;
 }
 
 int
 mono_vfree (void *addr, size_t length, MonoMemAccountType type)
 {
-	VallocInfo *info = (VallocInfo*)(valloc_hash ? g_hash_table_lookup (valloc_hash, addr) : NULL);
-
-	if (info) {
-		/*
-		 * We are passed the aligned address in the middle of the mapping allocated by
-		 * mono_valloc_align (), free the original mapping.
-		 */
-		BEGIN_CRITICAL_SECTION;
-		if (mono_opt_wasm_mmap)
-			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;
-		if (mono_opt_wasm_mmap)
-			mwpm_free_range (addr, length);
-		else
-			munmap (addr, length);
-		END_CRITICAL_SECTION;
-	}
+	// NOTE: this doesn't implement partial freeing like munmap does
+	// we set MS_BLOCK_ALLOC_NUM to 1 to avoid partial freeing
+	g_free (addr);
 
 	mono_account_mem (type, -(ssize_t)length);
 
@@ -267,6 +178,9 @@ mono_file_unmap (void *addr, void *handle)
 int
 mono_mprotect (void *addr, size_t length, int flags)
 {
+	if (flags & MONO_MMAP_DISCARD) {
+		memset (addr, 0, length);
+	}
 	return 0;
 }