RemoteCache: N-set caching

microsoft · Mar 17, 2024 · 114d0d0 · 114d0d0
1 parent a33436d
commit 114d0d0
Showing 1 changed file with 24 additions and 8 deletions.
diff --git a/src/snmalloc/mem/remotecache.h b/src/snmalloc/mem/remotecache.h
@@ -21,11 +21,15 @@ namespace snmalloc
  std::array<freelist::Builder<false>, REMOTE_SLOTS> list;
 
  static constexpr size_t RING_ASSOC = 2;
+ static constexpr size_t RING_SET_BITS = 4;
 
- std::array<freelist::Builder<false, true>, RING_ASSOC> open_builder;
- std::array<typename Config::PagemapEntry::SlabMetadata*, RING_ASSOC>
- open_meta = {nullptr};
- std::array<RemoteAllocator::alloc_id_t, RING_ASSOC> open_target = {0};
+ static constexpr size_t RINGS =
+ RING_ASSOC * bits::one_at_bit(RING_SET_BITS);
+
+ std::array<freelist::Builder<false, true>, RINGS> open_builder;
+ std::array<typename Config::PagemapEntry::SlabMetadata*, RINGS> open_meta =
+ {nullptr};
+ std::array<RemoteAllocator::alloc_id_t, RINGS> open_target = {0};
 
  /**
  * The total amount of memory we are waiting for before we will dispatch
@@ -109,6 +113,14 @@ namespace snmalloc
  open_target[ix] = id;
  }
 
+ SNMALLOC_FAST_PATH size_t
+ ring_way(typename Config::PagemapEntry::SlabMetadata* meta)
+ {
+ // See https://github.com/skeeto/hash-prospector for choice of constant
+ return ((meta->as_key_tweak() * 0x7EFB352D) >> 16) &
+ bits::mask_bits(RING_SET_BITS);
+ }
+
  template<size_t allocator_size>
  SNMALLOC_FAST_PATH void dealloc(
  typename Config::PagemapEntry::SlabMetadata* meta,
@@ -119,8 +131,11 @@ namespace snmalloc
 
  auto r = freelist::Object::make<capptr::bounds::AllocWild>(p);
 
- for (size_t ix = 0; ix < RING_ASSOC; ix++)
+ size_t ix_set = ring_way(meta);
+
+ for (size_t ix_way = 0; ix_way < RING_ASSOC; ix_way++)
  {
+ size_t ix = ix_set + ix_way;
  if (meta == open_meta[ix])
  {
  open_builder[ix].add(
@@ -129,10 +144,11 @@ namespace snmalloc
  }
  }
 
- size_t victim_ix = 0;
+ size_t victim_ix = ix_set;
  size_t victim_size = 0;
- for (size_t ix = 0; ix < RING_ASSOC; ix++)
+ for (size_t ix_way = 0; ix_way < RING_ASSOC; ix_way++)
  {
+ size_t ix = ix_set + ix_way;
  if (open_meta[ix] == nullptr)
  {
  victim_ix = ix;
@@ -173,7 +189,7 @@ namespace snmalloc
  };
 
  /* Close open rings */
- for (size_t ix = 0; ix < RING_ASSOC; ix++)
+ for (size_t ix = 0; ix < RINGS; ix++)
  {
  if (open_meta[ix] != nullptr)
  {