Share kPageSize (and other small tweaks) (#6443)

Summary:
Make kPageSize extern const size_t (used in draft https://github.com/facebook/rocksdb/issues/6427)
Make kLitteEndian constexpr bool
Clarify a couple of comments
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6443

Test Plan: make check, CI

Differential Revision: D20044558

Pulled By: pdillinger

fbshipit-source-id: e0c5cc13229c82726280dc0ddcba4078346b8418

env/env_test.cc

@@ -42,14 +42,10 @@
 #include "util/mutexlock.h"
 #include "util/string_util.h"
 
-#ifdef OS_LINUX
-static const size_t kPageSize = sysconf(_SC_PAGESIZE);
-#else
-static const size_t kPageSize = 4 * 1024;
-#endif
-
 namespace ROCKSDB_NAMESPACE {
 
+using port::kPageSize;
+
 static const int kDelayMicros = 100000;
 
 struct Deleter {
@@ -881,9 +877,10 @@ TEST_F(EnvPosixTest, PositionedAppend) {
   // Verify the above
   std::unique_ptr<SequentialFile> seq_file;
   ASSERT_OK(env_->NewSequentialFile(ift.name() + "/f", &seq_file, options));
-  char scratch[kPageSize * 2];
+  size_t scratch_len = kPageSize * 2;
+  std::unique_ptr<char[]> scratch(new char[scratch_len]);
   Slice result;
-  ASSERT_OK(seq_file->Read(sizeof(scratch), &result, scratch));
+  ASSERT_OK(seq_file->Read(scratch_len, &result, scratch.get()));
   ASSERT_EQ(kPageSize + kBlockSize, result.size());
   ASSERT_EQ('a', result[kBlockSize - 1]);
   ASSERT_EQ('b', result[kBlockSize]);
@@ -977,7 +974,6 @@ TEST_P(EnvPosixTestWithParam, AllocateTest) {
     // allocate 100 MB
     size_t kPreallocateSize = 100 * 1024 * 1024;
     size_t kBlockSize = 512;
-    size_t kPageSize = 4096;
     size_t kDataSize = 1024 * 1024;
     auto data_ptr = NewAligned(kDataSize, 'A');
     Slice data(data_ptr.get(), kDataSize);

include/rocksdb/advanced_options.h

@@ -151,7 +151,6 @@ enum UpdateStatus {    // Return status For inplace update callback
   UPDATED         = 2, // No inplace update. Merged value set
 };
 
-
 struct AdvancedColumnFamilyOptions {
   // The maximum number of write buffers that are built up in memory.
   // The default and the minimum number is 2, so that when 1 write buffer
@@ -330,10 +329,9 @@ struct AdvancedColumnFamilyOptions {
   std::shared_ptr<const SliceTransform>
       memtable_insert_with_hint_prefix_extractor = nullptr;
 
-  // Control locality of bloom filter probes to improve cache miss rate.
+  // Control locality of bloom filter probes to improve CPU cache hit rate.
-  // This option only applies to memtable prefix bloom and plaintable
+  // This option now only applies to plaintable prefix bloom. This
-  // prefix bloom. It essentially limits every bloom checking to one cache line.
+  // optimization is turned off when set to 0, and positive number to turn
-  // This optimization is turned off when set to 0, and positive number to turn
   // it on.
   // Default: 0
   uint32_t bloom_locality = 0;

include/rocksdb/filter_policy.h

@@ -84,7 +84,8 @@ class FilterBitsReader {
 };
 
 // Contextual information passed to BloomFilterPolicy at filter building time.
-// Used in overriding FilterPolicy::GetBuilderWithContext().
+// Used in overriding FilterPolicy::GetBuilderWithContext(). References other
+// structs because this is expected to be a temporary, stack-allocated object.
 struct FilterBuildingContext {
   // This constructor is for internal use only and subject to change.
   FilterBuildingContext(const BlockBasedTableOptions& table_options);

port/port_posix.cc

@@ -217,6 +217,18 @@ void cacheline_aligned_free(void *memblock) {
   free(memblock);
 }
 
+static size_t GetPageSize() {
+#if defined(OS_LINUX) || defined(_SC_PAGESIZE)
+  long v = sysconf(_SC_PAGESIZE);
+  if (v >= 1024) {
+    return static_cast<size_t>(v);
+  }
+#endif
+  // Default assume 4KB
+  return 4U * 1024U;
+}
+
+const size_t kPageSize = GetPageSize();
 
 }  // namespace port
 }  // namespace ROCKSDB_NAMESPACE

port/port_posix.h

@@ -99,7 +99,7 @@ const int64_t kMaxInt64 = std::numeric_limits<int64_t>::max();
 const int64_t kMinInt64 = std::numeric_limits<int64_t>::min();
 const size_t kMaxSizet = std::numeric_limits<size_t>::max();
 
-static const bool kLittleEndian = PLATFORM_IS_LITTLE_ENDIAN;
+constexpr bool kLittleEndian = PLATFORM_IS_LITTLE_ENDIAN;
 #undef PLATFORM_IS_LITTLE_ENDIAN
 
 class CondVar;
@@ -212,5 +212,7 @@ extern void Crash(const std::string& srcfile, int srcline);
 
 extern int GetMaxOpenFiles();
 
+extern const size_t kPageSize;
+
 } // namespace port
 }  // namespace ROCKSDB_NAMESPACE

port/win/port_win.cc

@@ -262,5 +262,8 @@ void Crash(const std::string& srcfile, int srcline) {
 
 int GetMaxOpenFiles() { return -1; }
 
+// Assume 4KB page size
+const size_t kPageSize = 4U * 1024U;
+
 }  // namespace port
 }  // namespace ROCKSDB_NAMESPACE

port/win/port_win.h

@@ -16,10 +16,6 @@
 #define WIN32_LEAN_AND_MEAN
 #endif
 
-// Assume that for everywhere
-#undef PLATFORM_IS_LITTLE_ENDIAN
-#define PLATFORM_IS_LITTLE_ENDIAN true
-
 #include <windows.h>
 #include <string>
 #include <string.h>
@@ -70,10 +66,6 @@ typedef SSIZE_T ssize_t;
 
 #endif
 
-#ifndef PLATFORM_IS_LITTLE_ENDIAN
-#define PLATFORM_IS_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
-#endif
-
 namespace ROCKSDB_NAMESPACE {
 
 #define PREFETCH(addr, rw, locality)
@@ -122,7 +114,10 @@ const size_t kMaxSizet = std::numeric_limits<size_t>::max();
 
 #endif //_MSC_VER
 
-const bool kLittleEndian = true;
+// "Windows is designed to run on little-endian computer architectures."
+// https://docs.microsoft.com/en-us/windows/win32/sysinfo/registry-value-types
+constexpr bool kLittleEndian = true;
+#undef PLATFORM_IS_LITTLE_ENDIAN
 
 class CondVar;
 
@@ -270,6 +265,8 @@ inline void cacheline_aligned_free(void *memblock) {
 #endif
 }
 
+extern const size_t kPageSize;
+
 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52991 for MINGW32
 // could not be worked around with by -mno-ms-bitfields
 #ifndef __MINGW32__