bindings for memory info (#761)

* bindings for memory info

* update api

* keep cache low if requested

* fix default

* nit in ops error

docs/src/index.rst

@@ -64,6 +64,7 @@ are the CPU and GPU.
    python/transforms
    python/fft
    python/linalg
+   python/metal
    python/nn
    python/optimizers
    python/tree_utils

docs/src/python/metal.rst

@@ -0,0 +1,14 @@
+Metal
+=====
+
+.. currentmodule:: mlx.core.metal
+
+.. autosummary:: 
+  :toctree: _autosummary
+
+  is_available
+  get_active_memory
+  get_peak_memory
+  get_cache_memory
+  set_memory_limit
+  set_cache_limit

docs/src/python/ops.rst

@@ -57,6 +57,7 @@ Operations
    greater_equal
    identity
    inner
+   isclose
    isnan
    isposinf
    isneginf
@@ -121,6 +122,7 @@ Operations
    tan
    tanh
    tensordot
+   tile
    transpose
    tri
    tril

mlx/backend/metal/allocator.cpp

@@ -1,4 +1,4 @@
-// Copyright © 2023 Apple Inc.
+// Copyright © 2023-2024 Apple Inc.
 
 #include "mlx/backend/metal/allocator.h"
 #include "mlx/backend/metal/metal.h"
@@ -23,16 +23,6 @@ void* Buffer::raw_ptr() {
 
 namespace metal {
 
-static bool cache_enabled_ = true;
-
-bool cache_enabled() {
-  return cache_enabled_;
-}
-
-void set_cache_enabled(bool enabled) {
-  cache_enabled_ = enabled;
-}
-
 namespace {
 
 BufferCache::BufferCache(MTL::Device* device)
@@ -158,9 +148,23 @@ void BufferCache::remove_from_list(BufferCache::BufferHolder* to_remove) {
 MetalAllocator::MetalAllocator()
     : device_(device(mlx::core::Device::gpu).mtl_device()),
       buffer_cache_(device_),
-      peak_allocated_size_(0),
       block_limit_(1.5 * device_->recommendedMaxWorkingSetSize()),
-      gc_limit_(0.95 * device_->recommendedMaxWorkingSetSize()) {}
+      gc_limit_(0.95 * device_->recommendedMaxWorkingSetSize()),
+      max_pool_size_(block_limit_) {}
+
+size_t MetalAllocator::set_cache_limit(size_t limit) {
+  std::swap(limit, max_pool_size_);
+  return limit;
+};
+
+size_t MetalAllocator::set_memory_limit(size_t limit, bool relaxed) {
+  std::swap(limit, block_limit_);
+  relaxed_ = relaxed;
+  gc_limit_ = std::min(
+      block_limit_,
+      static_cast<size_t>(0.95 * device_->recommendedMaxWorkingSetSize()));
+  return limit;
+};
 
 Buffer MetalAllocator::malloc(size_t size, bool allow_swap /* = false */) {
   // Metal doesn't like empty buffers
@@ -175,10 +179,12 @@ Buffer MetalAllocator::malloc(size_t size, bool allow_swap /* = false */) {
 
   // Try the cache
   MTL::Buffer* buf = buffer_cache_.reuse_from_cache(size);
-
+  size_t pool_size = get_cache_memory();
   if (!buf) {
+    size_t mem_required = get_active_memory() + pool_size + size;
+
     // If there is too much memory pressure, fail (likely causes a wait).
-    if (!allow_swap && device_->currentAllocatedSize() + size >= block_limit_) {
+    if (!(allow_swap && relaxed_) && mem_required >= block_limit_) {
       return Buffer{nullptr};
     }
 
@@ -186,10 +192,8 @@ Buffer MetalAllocator::malloc(size_t size, bool allow_swap /* = false */) {
 
     // If we have a lot of memory pressure, check if we can reclaim some memory
     // from the cache
-    if (device_->currentAllocatedSize() + size >= gc_limit_) {
-      size_t min_bytes_to_free =
-          size + device_->currentAllocatedSize() - gc_limit_;
-      buffer_cache_.release_cached_buffers(min_bytes_to_free);
+    if (mem_required >= gc_limit_) {
+      buffer_cache_.release_cached_buffers(mem_required - gc_limit_);
     }
 
     // Allocate new buffer if needed
@@ -198,15 +202,22 @@ Buffer MetalAllocator::malloc(size_t size, bool allow_swap /* = false */) {
     buf = device_->newBuffer(size, res_opt);
   }
 
-  peak_allocated_size_ =
-      std::max(peak_allocated_size_, device_->currentAllocatedSize());
+  // Maintain the cache below the requested limit
+  if (pool_size >= max_pool_size_) {
+    auto thread_pool = metal::new_scoped_memory_pool();
+    buffer_cache_.release_cached_buffers(pool_size - max_pool_size_);
+  }
+
+  active_memory_ += buf->length();
+  peak_memory_ = std::max(peak_memory_, active_memory_);
 
   return Buffer{static_cast<void*>(buf)};
 }
 
 void MetalAllocator::free(Buffer buffer) {
   auto buf = static_cast<MTL::Buffer*>(buffer.ptr());
-  if (cache_enabled()) {
+  active_memory_ -= buf->length();
+  if (max_pool_size_ > 0) {
     buffer_cache_.recycle_to_cache(buf);
   } else {
     buf->release();
@@ -218,6 +229,22 @@ MetalAllocator& allocator() {
   return allocator_;
 }
 
+size_t set_cache_limit(size_t limit) {
+  return allocator().set_cache_limit(limit);
+}
+size_t set_memory_limit(size_t limit, bool relaxed /* = true */) {
+  return allocator().set_memory_limit(limit, relaxed);
+}
+size_t get_active_memory() {
+  return allocator().get_active_memory();
+}
+size_t get_peak_memory() {
+  return allocator().get_peak_memory();
+}
+size_t get_cache_memory() {
+  return allocator().get_cache_memory();
+}
+
 } // namespace metal
 
 } // namespace mlx::core

mlx/backend/metal/allocator.h

@@ -1,4 +1,4 @@
-// Copyright © 2023 Apple Inc.
+// Copyright © 2023-2024 Apple Inc.
 
 #pragma once
 
@@ -24,6 +24,9 @@ class BufferCache {
   MTL::Buffer* reuse_from_cache(size_t size);
   void recycle_to_cache(MTL::Buffer* buf);
   void release_cached_buffers(size_t min_bytes_to_free);
+  size_t pool_size() {
+    return pool_size_;
+  }
 
  private:
   struct BufferHolder {
@@ -54,6 +57,17 @@ class MetalAllocator : public allocator::Allocator {
  public:
   virtual Buffer malloc(size_t size, bool allow_swap = false) override;
   virtual void free(Buffer buffer) override;
+  size_t get_active_memory() {
+    return active_memory_;
+  };
+  size_t get_peak_memory() {
+    return peak_memory_;
+  };
+  size_t get_cache_memory() {
+    return buffer_cache_.pool_size();
+  };
+  size_t set_cache_limit(size_t limit);
+  size_t set_memory_limit(size_t limit, bool relaxed);
 
  private:
   MTL::Device* device_;
@@ -64,9 +78,12 @@ class MetalAllocator : public allocator::Allocator {
   BufferCache buffer_cache_;
 
   // Allocation stats
-  size_t peak_allocated_size_;
   size_t block_limit_;
   size_t gc_limit_;
+  size_t active_memory_{0};
+  size_t peak_memory_{0};
+  size_t max_pool_size_;
+  bool relaxed_{true};
 };
 
 MetalAllocator& allocator();

mlx/backend/metal/metal.h

@@ -12,8 +12,51 @@
 namespace mlx::core::metal {
 
 bool is_available();
-bool cache_enabled(void);
-void set_cache_enabled(bool enabled);
+
+/* Get the actively used memory in bytes.
+ *
+ * Note, this will not always match memory use reported by the system because
+ * it does not include cached memory buffers.
+ * */
+size_t get_active_memory();
+
+/* Get the peak amount of used memory in bytes.
+ *
+ * The maximum memory used is recorded from the beginning of the program
+ * execution.
+ * */
+size_t get_peak_memory();
+
+/* Get the cache size in bytes.
+ *
+ * The cache includes memory not currently used that has not been returned
+ * to the system allocator.
+ * */
+size_t get_cache_memory();
+
+/* Set the memory limit.
+ * Calls to malloc will wait on scheduled tasks if the limit is exceeded.  If
+ * there are no more scheduled tasks an error will be raised if relaxed
+ * is false or memory will be allocated (including the potential for
+ * swap) if relaxed is true.
+ *
+ * The memory limit defaults to 1.5 times the maximum recommended working set
+ * size reported by the device.
+ *
+ * Returns the previous memory limit.
+ * */
+size_t set_memory_limit(size_t limit, bool relaxed = true);
+
+/* Set the free cache limit.
+ * If using more than the given limit, free memory will be reclaimed
+ * from the cache on the next allocation. To disable the cache,
+ * set the limit to 0.
+ *
+ * The cache limit defaults to the memory limit.
+ *
+ * Returns the previous cache limit.
+ * */
+size_t set_cache_limit(size_t limit);
 
 void new_stream(Stream stream);
 std::shared_ptr<void> new_scoped_memory_pool();

mlx/backend/no_metal/metal.cpp

@@ -23,10 +23,21 @@ std::function<void()> make_task(
       "[metal::make_task] Cannot make GPU task without metal backend");
 }
 
-// No cache for CPU only
-bool cache_enabled(void) {
-  return false;
+// No-ops when Metal is not available.
+size_t get_active_memory() {
+  return 0;
+}
+size_t get_peak_memory() {
+  return 0;
+}
+size_t get_cache_memory() {
+  return 0;
+}
+size_t set_memory_limit(size_t, bool) {
+  return 0;
+}
+size_t set_cache_limit(size_t) {
+  return 0;
 }
-void set_cache_enabled(bool) {}
 
 } // namespace mlx::core::metal

python/src/metal.cpp

@@ -5,18 +5,88 @@
 #include "mlx/backend/metal/metal.h"
 
 namespace py = pybind11;
+using namespace py::literals;
 
 using namespace mlx::core;
 
 void init_metal(py::module_& m) {
   py::module_ metal = m.def_submodule("metal", "mlx.metal");
-  metal.def("is_available", &metal::is_available);
   metal.def(
-      "cache_enabled",
-      &metal::cache_enabled,
-      "check if metal buffer cache is enabled, default is true");
+      "is_available",
+      &metal::is_available,
+      R"pbdoc(
+      Check if the Metal back-end is available.
+      )pbdoc");
   metal.def(
-      "set_cache_enabled",
-      &metal::set_cache_enabled,
-      "enable or disable metal buffer cache");
+      "get_active_memory",
+      &metal::get_active_memory,
+      R"pbdoc(
+      Get the actively used memory in bytes.
+
+      Note, this will not always match memory use reported by the system because
+      it does not include cached memory buffers.
+      )pbdoc");
+  metal.def(
+      "get_peak_memory",
+      &metal::get_peak_memory,
+      R"pbdoc(
+      Get the peak amount of used memory in bytes.
+
+      The maximum memory used is recorded from the beginning of the program
+      execution.
+      )pbdoc");
+  metal.def(
+      "get_cache_memory",
+      &metal::get_cache_memory,
+      R"pbdoc(
+      Get the cache size in bytes.
+
+      The cache includes memory not currently used that has not been returned
+      to the system allocator.
+      )pbdoc");
+  metal.def(
+      "set_memory_limit",
+      &metal::set_memory_limit,
+      "limit"_a,
+      py::kw_only(),
+      "relaxed"_a = true,
+      R"pbdoc(
+      Set the memory limit.
+
+      Memory allocations will wait on scheduled tasks to complete if the limit
+      is exceeded. If there are no more scheduled tasks an error will be raised
+      if ``relaxed`` is ``False``. Otherwise memory will be allocated
+      (including the potential for swap) if ``relaxed`` is ``True``.
+
+      The memory limit defaults to 1.5 times the maximum recommended working set
+      size reported by the device.
+
+      Args:
+        limit (int): Memory limit in bytes.
+        relaxed (bool, optional): If `False`` an error is raised if the limit
+          is exceeded. Default: ``True``
+
+      Returns:
+        int: The previous memory limit in bytes.
+      )pbdoc");
+  metal.def(
+      "set_cache_limit",
+      &metal::set_cache_limit,
+      "limit"_a,
+      R"pbdoc(
+      Set the free cache limit.
+
+      If using more than the given limit, free memory will be reclaimed
+      from the cache on the next allocation. To disable the cache, set
+      the limit to ``0``.
+
+      The cache limit defaults to the memory limit. See
+      :func:`set_memory_limit` for more details.
+
+      Args:
+        limit (int): The cache limit in bytes.
+
+      Returns:
+        int: The previous cache limit in bytes.
+      )pbdoc");
 }

python/tests/test_metal.py

@@ -0,0 +1,45 @@
+# Copyright © 2023-2024 Apple Inc.
+
+import unittest
+
+import mlx.core as mx
+import mlx_tests
+
+
+class TestMetal(mlx_tests.MLXTestCase):
+
+    @unittest.skipIf(not mx.metal.is_available(), "Metal is not available")
+    def test_memory_info(self):
+        old_limit = mx.metal.set_cache_limit(0)
+
+        a = mx.zeros((4096,))
+        mx.eval(a)
+        del a
+        self.assertEqual(mx.metal.get_cache_memory(), 0)
+        self.assertEqual(mx.metal.set_cache_limit(old_limit), 0)
+        self.assertEqual(mx.metal.set_cache_limit(old_limit), old_limit)
+
+        old_limit = mx.metal.set_memory_limit(10)
+        self.assertTrue(mx.metal.set_memory_limit(old_limit), 10)
+        self.assertTrue(mx.metal.set_memory_limit(old_limit), old_limit)
+
+        # Query active and peak memory
+        a = mx.zeros((4096,))
+        mx.eval(a)
+        active_mem = mx.metal.get_active_memory()
+        self.assertTrue(active_mem >= 4096 * 4)
+
+        b = mx.zeros((4096,))
+        mx.eval(b)
+        del b
+
+        new_active_mem = mx.metal.get_active_memory()
+        self.assertEqual(new_active_mem, active_mem)
+        peak_mem = mx.metal.get_peak_memory()
+        self.assertTrue(peak_mem >= 4096 * 8)
+        cache_mem = mx.metal.get_cache_memory()
+        self.assertTrue(cache_mem >= 4096 * 4)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/metal_tests.cpp

@@ -1,4 +1,4 @@
-// Copyright © 2023 Apple Inc.
+// Copyright © 2023-2024 Apple Inc.
 
 #include <array>
 #include "doctest/doctest.h"
@@ -473,41 +473,42 @@ TEST_CASE("test metal validation") {
   eval(scatter_max(array(1), {}, array(2), std::vector<int>{}));
 }
 
-TEST_CASE("test metal enable/disable cache") {
-  // Test enable metal cache
+TEST_CASE("test metal memory info") {
+  // Test cache limits
   {
-    metal::set_cache_enabled(true);
-    CHECK(metal::cache_enabled());
-
-    auto& a = metal::allocator();
-    auto size = 100;
-    auto buf = a.malloc(size, false);
-
-    // Release a
-    a.free(buf);
-
-    // Check size should equals to size
-    CHECK_EQ(static_cast<MTL::Buffer*>(buf.ptr())->length(), size);
-  }
-
-  // Test disable metal cache
+    auto old_limit = metal::set_cache_limit(0);
     {
-    metal::set_cache_enabled(false);
-    CHECK(!metal::cache_enabled());
+      auto a = zeros({4096});
+      eval(a);
+    }
+    CHECK_EQ(metal::get_cache_memory(), 0);
+    CHECK_EQ(metal::set_cache_limit(old_limit), 0);
+    CHECK_EQ(metal::set_cache_limit(old_limit), old_limit);
+  }
 
-    auto& a = metal::allocator();
-    auto size = 100;
-    auto buf = a.malloc(size, false);
-    auto buf_ptr = static_cast<MTL::Buffer*>(buf.ptr());
-    unsigned char first_byte = *reinterpret_cast<unsigned char*>(buf_ptr);
+  // Test memory limits
+  {
+    auto old_limit = metal::set_memory_limit(10);
+    CHECK_EQ(metal::set_memory_limit(old_limit), 10);
+    CHECK_EQ(metal::set_memory_limit(old_limit), old_limit);
+  }
 
-    // Release a
-    a.free(buf);
+  // Query active and peak memory
+  {
+    auto a = zeros({4096});
+    eval(a);
+    auto active_mem = metal::get_active_memory();
+    CHECK(active_mem >= 4096 * 4);
+    {
+      auto b = zeros({4096});
+      eval(b);
+    }
+    auto new_active_mem = metal::get_active_memory();
+    CHECK_EQ(new_active_mem, active_mem);
+    auto peak_mem = metal::get_peak_memory();
+    CHECK(peak_mem >= 4096 * 8);
 
-    // If release successfully, the first byte should be different from the
-    // first byte before release
-    unsigned char new_first_byte = *reinterpret_cast<unsigned char*>(buf_ptr);
-
-    CHECK_NE(new_first_byte, first_byte);
+    auto cache_mem = metal::get_cache_memory();
+    CHECK(cache_mem >= 4096 * 4);
   }
 }