Make text section 2MB aligned for hugepages.

chromeos/hugepage_text/hugepage_text.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // Author: Ken Chen <kenchen@google.com>
 //
 // hugepage text library to remap process executable segment with hugepages.
 
 #include "chromeos/hugepage_text/hugepage_text.h"
 
 #include <link.h>
@@ skipping 154 matching lines @@
 }
 
 // Top level text remapping function.
 //
 // Inputs: vaddr, the starting virtual address to remap to hugepage
 //         hsize, size of the memory segment to remap in bytes
 // Return: none
 // Effect: physical backing page changed from small page to hugepage. If there
 //         are error condition, the remaping operation is aborted.
 static void RemapHugetlbText(void* vaddr, const size_t segsize) {
-  int hsize = segsize;
+  // remove unaligned head regions
+  size_t head_gap = (kHpageSize - (size_t)addr % kHpageSize) % kHpageSize;

[kenchen, 2016/01/22 22:19:42]

This should vaddr and the last mod operation is not necessary.

[yunlian, 2016/01/22 22:27:00]

Yes, the vaddr is part is done. The last mod is useful when the vaddr is 2MB
aligned. In this case, the head_gap is 0 instead of kHpageSize

+  size_t addr = (size_t)vaddr + head_gap;
+
+  int hsize = segsize - head_gap;
   if (segsize > kHpageSize * kNumHugePages)
     hsize = kHpageSize * kNumHugePages;
   hsize = hsize & kHpageMask;
 
   if (hsize == 0)
     return;
 
-  MremapHugetlbText(vaddr, hsize);
+  MremapHugetlbText((void *)addr, hsize);
 }
 
 // For a given ELF program header descriptor, iterates over all segments within
 // it and find the first segment that has PT_LOAD and is executable, call
 // RemapHugetlbText().
 //
 // Inputs: info: pointer to a struct dl_phdr_info that describes the DSO.
 //         size: size of the above structure (not used in this function).
 //         data: user param (not used in this function).
 // Return: always return true.  The value is propagated by dl_iterate_phdr().
@@ skipping 18 matching lines @@
 
 // Main library function.  This function will iterate all ELF segments and
 // attempt to remap text segment from small page to hugepage.
 // If remapping is successful.  All error conditions are soft fail such that
 // effect will be rolled back and remap operation will be aborted.
 void ReloadElfTextInHugePages(void) {
   dl_iterate_phdr(FilterElfHeader, 0);
 }
 
 }  // namespace chromeos