[heap] Use twice less Freelists categories

Our current Freelist uses 47 categories. Because FreeListCategory is
about 26 bytes or so, this causes a non-neglieable overhead per
page. This CL divides by two the number of categories used.

Benchmark have shown that this should not increase old heap size. And
since less categories will be used, size of mallocated objects will be
smaller.
Furthermore,in both precise and fast modes, Scavenger time is lower
when using 24 Freelists rather than 47.

Bug: v8:9329
Change-Id: I81cca63a0ffd0aad5f9e009a176f401f2299493d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1778941
Commit-Queue: Darius Mercadier <dmercadier@google.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63483}

src/heap/spaces.h

@@ -1922,8 +1922,8 @@ class V8_EXPORT_PRIVATE FreeListFastAlloc : public FreeList {
   }
 };
 
-// Use 47 Freelists: on per size between 24 and 256, and then a few ones for
-// larger sizes. See the variable |categories_max| for the size of each
+// Use 24 Freelists: on per 16 bytes between 24 and 256, and then a few ones for
+// larger sizes. See the variable |categories_min| for the size of each
 // Freelist.  Allocation is done using a best-fit strategy (considering only the
 // first element of each category though).
 // Performances are expected to be worst than FreeListLegacy, but memory
@@ -1953,28 +1953,25 @@ class V8_EXPORT_PRIVATE FreeListMany : public FreeList {
 
   // Categories boundaries generated with:
   // perl -E '
-  //   @cat = map {$_*8} 3..32, 48, 64;
-  //   while ($cat[-1] <= 32768) {
-  //     push @cat, $cat[-1]+$cat[-3], $cat[-1]*2
-  //   }
-  //   say join ", ", @cat;
-  //   say "\n", scalar @cat'
-  static const int kNumberOfCategories = 46;
+  //      @cat = (24, map {$_*16} 2..16, 48, 64);
+  //      while ($cat[-1] <= 32768) {
+  //        push @cat, $cat[-1]*2
+  //      }
+  //      say join ", ", @cat;
+  //      say "\n", scalar @cat'
+  static const int kNumberOfCategories = 24;
   static constexpr unsigned int categories_min[kNumberOfCategories] = {
-      24,    32,    40,    48,    56,    64,   72,   80,   88,   96,
-      104,   112,   120,   128,   136,   144,  152,  160,  168,  176,
-      184,   192,   200,   208,   216,   224,  232,  240,  248,  256,
-      384,   512,   768,   1024,  1536,  2048, 3072, 4096, 6144, 8192,
-      12288, 16384, 24576, 32768, 49152, 65536};
+      24,  32,  48,  64,  80,  96,   112,  128,  144,  160,   176,   192,
+      208, 224, 240, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536};
 
   // Return the smallest category that could hold |size_in_bytes| bytes.
   FreeListCategoryType SelectFreeListCategoryType(
       size_t size_in_bytes) override {
     if (size_in_bytes <= kPreciseCategoryMaxSize) {
       if (size_in_bytes < categories_min[1]) return 0;
-      return static_cast<FreeListCategoryType>(size_in_bytes >> 3) - 3;
+      return static_cast<FreeListCategoryType>(size_in_bytes >> 4) - 1;
     }
-    for (int cat = (kPreciseCategoryMaxSize >> 3) - 3; cat < last_category_;
+    for (int cat = (kPreciseCategoryMaxSize >> 4) - 1; cat < last_category_;
          cat++) {
       if (size_in_bytes < categories_min[cat + 1]) {
         return cat;
@@ -2078,13 +2075,13 @@ class V8_EXPORT_PRIVATE FreeListManyCachedFastPath : public FreeListManyCached {
                                            AllocationOrigin origin) override;
 
  protected:
-  // Objects in the 36th category are at least 2048 bytes
-  static const FreeListCategoryType kFastPathFirstCategory = 35;
+  // Objects in the 18th category are at least 2048 bytes
+  static const FreeListCategoryType kFastPathFirstCategory = 18;
   static const size_t kFastPathStart = 2048;
   static const size_t kTinyObjectMaxSize = 128;
   static const size_t kFastPathOffset = kFastPathStart - kTinyObjectMaxSize;
-  // Objects in the 30th category are at least 256 bytes
-  static const FreeListCategoryType kFastPathFallBackTiny = 29;
+  // Objects in the 15th category are at least 256 bytes
+  static const FreeListCategoryType kFastPathFallBackTiny = 15;
 
   STATIC_ASSERT(categories_min[kFastPathFirstCategory] == kFastPathStart);
   STATIC_ASSERT(categories_min[kFastPathFallBackTiny] ==