mfbt/TaggedAnonymousMemory.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 // Linux kernels since 5.17 have a feature for assigning names to
   8 // ranges of anonymous memory (i.e., memory that doesn't have a "name"
   9 // in the form of an underlying mapped file).  These names are
  10 // reported in /proc/<pid>/smaps alongside system-level memory usage
  11 // information such as Proportional Set Size (memory usage adjusted
  12 // for sharing between processes), which allows reporting this
  13 // information at a finer granularity than would otherwise be possible
  14 // (e.g., separating malloc() heap from JS heap).
  15 //
  16 // Existing memory can be tagged with MozTagAnonymousMemory(); it will
  17 // tag the range of complete pages containing the given interval, so
  18 // the results may be inexact if the range isn't page-aligned.
  19 // MozTaggedAnonymousMmap() can be used like mmap() with an extra
  20 // parameter, and will tag the returned memory if the mapping was
  21 // successful (and if it was in fact anonymous).
  22 //
  23 // NOTE: The pointer given as the "tag" argument MUST remain valid as
  24 // long as the mapping exists.  The referenced string is read when
  25 // /proc/<pid>/smaps or /proc/<pid>/maps is read, not when the tag is
  26 // established, so freeing it or changing its contents will have
  27 // unexpected results.  Using a static string is probably best.
  28 //
  29 // Also note that this header can be used by both C and C++ code.
  30
  31 #ifndef mozilla_TaggedAnonymousMemory_h
  32 #define mozilla_TaggedAnonymousMemory_h
  33
  34 #ifndef XP_WIN
  35
  36 #  ifdef __wasi__
  37 #    include <stdlib.h>
  38 #  else
  39 #    include <sys/types.h>
  40 #    include <sys/mman.h>
  41 #  endif  // __wasi__
  42
  43 #  include "mozilla/Types.h"
  44
  45 #  ifdef XP_LINUX
  46
  47 #    ifdef __cplusplus
  48 extern "C" {
  49 #    endif
  50
  51 MFBT_API void MozTagAnonymousMemory(const void* aPtr, size_t aLength,
  52                                     const char* aTag);
  53
  54 MFBT_API void* MozTaggedAnonymousMmap(void* aAddr, size_t aLength, int aProt,
  55                                       int aFlags, int aFd, off_t aOffset,
  56                                       const char* aTag);
  57
  58 #    ifdef __cplusplus
  59 }  // extern "C"
  60 #    endif
  61
  62 #  else  // XP_LINUX
  63
  64 static inline void MozTagAnonymousMemory(const void* aPtr, size_t aLength,
  65                                          const char* aTag) {}
  66
  67 static inline void* MozTaggedAnonymousMmap(void* aAddr, size_t aLength,
  68                                            int aProt, int aFlags, int aFd,
  69                                            off_t aOffset, const char* aTag) {
  70 #    ifdef __wasi__
  71   MOZ_CRASH("We don't use this memory for WASI right now.");
  72   return nullptr;
  73 #    else
  74   return mmap(aAddr, aLength, aProt, aFlags, aFd, aOffset);
  75 #    endif
  76 }
  77
  78 #  endif  // XP_LINUX
  79
  80 #endif  // !XP_WIN
  81
  82 #endif  // mozilla_TaggedAnonymousMemory_h