From 49412d93e27ebb69eccddc966c7101f69abb6e65 Mon Sep 17 00:00:00 2001
From: Aaron Gao <gzh@fb.com>
Date: Thu, 4 May 2017 01:21:31 -0700
Subject: [PATCH] fix memory alignment with logical sector size

Summary:
we align the buffer with logical sector size and should not test it with page size, which is usually 4k.
Closes https://github.com/facebook/rocksdb/pull/2245

Differential Revision: D5001842

Pulled By: lightmark

fbshipit-source-id: a7135fcf6351c6db363e8908956b1e193a4a6291
---
 env/io_posix.cc | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/env/io_posix.cc b/env/io_posix.cc
index 2fc7ad533..b978885b1 100644
--- a/env/io_posix.cc
+++ b/env/io_posix.cc
@@ -115,18 +115,13 @@ size_t GetLogicalBufferSize(int __attribute__((__unused__)) fd) {
  */
 #ifndef NDEBUG
 namespace {
-#ifdef OS_LINUX
-const size_t kPageSize = sysconf(_SC_PAGESIZE);
-#else
-const size_t kPageSize = 4 * 1024;
-#endif
 
 bool IsSectorAligned(const size_t off, size_t sector_size) {
   return off % sector_size == 0;
 }
 
-static bool IsPageAligned(const void* ptr) {
-  return uintptr_t(ptr) % (kPageSize) == 0;
+bool IsSectorAligned(const void* ptr, size_t sector_size) {
+  return uintptr_t(ptr) % sector_size == 0;
 }
 
 }
@@ -182,6 +177,11 @@ Status PosixSequentialFile::Read(size_t n, Slice* result, char* scratch) {
 
 Status PosixSequentialFile::PositionedRead(uint64_t offset, size_t n,
                                            Slice* result, char* scratch) {
+  if (use_direct_io()) {
+    assert(IsSectorAligned(offset, GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(n, GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(scratch, GetRequiredBufferAlignment()));
+  }
   Status s;
   ssize_t r = -1;
   size_t left = n;
@@ -306,6 +306,11 @@ PosixRandomAccessFile::~PosixRandomAccessFile() { close(fd_); }
 
 Status PosixRandomAccessFile::Read(uint64_t offset, size_t n, Slice* result,
                                    char* scratch) const {
+  if (use_direct_io()) {
+    assert(IsSectorAligned(offset, GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(n, GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(scratch, GetRequiredBufferAlignment()));
+  }
   Status s;
   ssize_t r = -1;
   size_t left = n;
@@ -704,9 +709,10 @@ PosixWritableFile::~PosixWritableFile() {
 }
 
 Status PosixWritableFile::Append(const Slice& data) {
-  assert(!use_direct_io() ||
-         (IsSectorAligned(data.size(), GetRequiredBufferAlignment()) &&
-          IsPageAligned(data.data())));
+  if (use_direct_io()) {
+    assert(IsSectorAligned(data.size(), GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(data.data(), GetRequiredBufferAlignment()));
+  }
   const char* src = data.data();
   size_t left = data.size();
   while (left != 0) {
@@ -725,10 +731,11 @@ Status PosixWritableFile::Append(const Slice& data) {
 }
 
 Status PosixWritableFile::PositionedAppend(const Slice& data, uint64_t offset) {
-  assert(use_direct_io() &&
-         IsSectorAligned(offset, GetRequiredBufferAlignment()) &&
-         IsSectorAligned(data.size(), GetRequiredBufferAlignment()) &&
-         IsPageAligned(data.data()));
+  if (use_direct_io()) {
+    assert(IsSectorAligned(offset, GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(data.size(), GetRequiredBufferAlignment()));
+    assert(IsSectorAligned(data.data(), GetRequiredBufferAlignment()));
+  }
   assert(offset <= std::numeric_limits<off_t>::max());
   const char* src = data.data();
   size_t left = data.size();