Improved pal_supports

src/mem/alloc.h

@@ -46,8 +46,7 @@ namespace snmalloc
 // Use flat map is under a single node.
 #  define SNMALLOC_MAX_FLATPAGEMAP_SIZE PAGEMAP_NODE_SIZE
 #endif
-  static constexpr bool USE_FLATPAGEMAP =
-    (Pal::pal_features & PalFeatures::LazyCommit) ||
+  static constexpr bool USE_FLATPAGEMAP = pal_supports<LazyCommit>() ||
     (SNMALLOC_MAX_FLATPAGEMAP_SIZE >=
      sizeof(FlatPagemap<SUPERSLAB_BITS, uint8_t>));
 
@@ -1209,9 +1208,7 @@ namespace snmalloc
           else if constexpr (decommit_strategy == DecommitSuperLazy)
           {
             static_assert(
-              std::remove_reference_t<decltype(
-                large_allocator.memory_provider)>::
-                template pal_supports<LowMemoryNotification>(),
+              pal_supports<LowMemoryNotification, MemoryProvider>(),
               "A lazy decommit strategy cannot be implemented on platforms "
               "without low memory notifications");
           }

src/mem/largealloc.h

@@ -175,15 +175,6 @@ namespace snmalloc
       return new (p) T(std::forward<Args...>(args)...);
     }
 
-    /**
-     * Query whether the PAL supports a specific feature.
-     */
-    template<PalFeatures F>
-    constexpr static bool pal_supports()
-    {
-      return (PAL::pal_features & F) == F;
-    }
-
     /**
      * Returns the number of low memory notifications that have been received
      * (over the lifetime of this process).  If the underlying system does not
@@ -192,7 +183,7 @@ namespace snmalloc
     SNMALLOC_FAST_PATH
     uint64_t low_memory_epoch()
     {
-      if constexpr (pal_supports<LowMemoryNotification>())
+      if constexpr (pal_supports<LowMemoryNotification, PAL>())
       {
         return PAL::low_memory_epoch();
       }
@@ -205,7 +196,7 @@ namespace snmalloc
     template<bool committed>
     void* reserve(size_t* size, size_t align) noexcept
     {
-      if constexpr (pal_supports<AlignedAllocation>())
+      if constexpr (pal_supports<AlignedAllocation, PAL>())
       {
         return PAL::template reserve<committed>(size, align);
       }

src/pal/pal.h

@@ -50,4 +50,13 @@ namespace snmalloc
   {
     Pal::error(str);
   }
+
+  /**
+   * Query whether the PAL supports a specific feature.
+   */
+  template<PalFeatures F, typename PAL = Pal>
+  constexpr static bool pal_supports()
+  {
+    return (PAL::pal_features & F) == F;
+  }
 } // namespace snmalloc

src/pal/pal_consts.h

@@ -28,8 +28,8 @@ namespace snmalloc
     AlignedAllocation = (1 << 1),
     /**
      * This PAL natively supports lazy commit of pages. This means have large
-     * allocations and not touching them does not up memory usage.  This is
-     * exposed in the P
+     * allocations and not touching them does not increase memory usage. This is
+     * exposed in the Pal.
      */
     LazyCommit = (1 << 2),
   };