src/memfs_malloc.cc

// Copyright (c) 2007, Google Inc.
// All rights reserved.
// 
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// modification, are permitted provided that the following conditions are
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// 
//     * Redistributions of source code must retain the above copyright
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// in the documentation and/or other materials provided with the
// distribution.
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Arun Sharma
//
// A tcmalloc system allocator that uses a memory based filesystem such as
// tmpfs or hugetlbfs
//
// Since these only exist on linux, we only register this allocator there.

#ifdef __linux

#include "config.h"
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/vfs.h>           // for statfs
#include <string>

#include "base/basictypes.h"
#include "base/googleinit.h"
#include "base/logging.h"
#include "base/sysinfo.h"
#include "system-alloc.h"

using std::string;

DEFINE_string(memfs_malloc_path, EnvToString("TCMALLOC_MEMFS_MALLOC_PATH", ""),
              "Path where hugetlbfs or tmpfs is mounted. The caller is "
              "responsible for ensuring that the path is unique and does "
              "not conflict with another process");

// Hugetlbfs based allocator for tcmalloc
class HugetlbSysAllocator: public SysAllocator {
public:
  HugetlbSysAllocator(int fd, int page_size)
    : big_page_size_(page_size),
      hugetlb_fd_(fd),
      hugetlb_base_(0) {
  }

  void* Alloc(size_t size, size_t *actual_size, size_t alignment);

private:
  int64 big_page_size_;
  int hugetlb_fd_;      // file descriptor for hugetlb
  off_t hugetlb_base_;
};

// No locking needed here since we assume that tcmalloc calls
// us with an internal lock held (see tcmalloc/system-alloc.cc).
void* HugetlbSysAllocator::Alloc(size_t size, size_t *actual_size,
                                 size_t alignment) {

  // We don't respond to allocation requests smaller than big_page_size_ unless
  // the caller is willing to take more than they asked for.
  if (actual_size == NULL && size < big_page_size_) {
    return NULL;
  }

  // Enforce huge page alignment.  Be careful to deal with overflow.
  if (alignment < big_page_size_) alignment = big_page_size_;
  size_t aligned_size = ((size + alignment - 1) / alignment) * alignment;
  if (aligned_size < size) {
    return NULL;
  }
  size = aligned_size;

  // Ask for extra memory if alignment > pagesize
  size_t extra = 0;
  if (alignment > big_page_size_) {
    extra = alignment - big_page_size_;
  }

  // This is not needed for hugetlbfs, but needed for tmpfs.  Annoyingly
  // hugetlbfs returns EINVAL for ftruncate.
  int ret = ftruncate(hugetlb_fd_, hugetlb_base_ + size + extra);
  if (ret != 0 && errno != EINVAL) {
    failed_ = true;
    return NULL;
  }

  // Note: size + extra does not overflow since:
  //            size + alignment < (1<<NBITS).
  // and        extra <= alignment
  // therefore  size + extra < (1<<NBITS)
  void *result = mmap(0, size + extra, PROT_WRITE|PROT_READ,
                      MAP_SHARED, hugetlb_fd_, hugetlb_base_);
  if (result == reinterpret_cast<void*>(MAP_FAILED)) {
    failed_ = true;
    return NULL;
  }
  uintptr_t ptr = reinterpret_cast<uintptr_t>(result);

  // Adjust the return memory so it is aligned
  size_t adjust = 0;
  if ((ptr & (alignment - 1)) != 0) {
    adjust = alignment - (ptr & (alignment - 1));
  }
  ptr += adjust;
  hugetlb_base_ += (size + extra);

  if (actual_size) {
    *actual_size = size + extra - adjust;
  }

  return reinterpret_cast<void*>(ptr);
}

static void InitSystemAllocator() {
  if (FLAGS_memfs_malloc_path.length()) {
    // Don't rely on the caller to ensure unique path name
    char pid[64];              // pids are smaller than this!
    int n = snprintf(pid, sizeof(pid), "%u", (unsigned int)(getpid()));
    CHECK(n < sizeof(pid));
    string hugetlbfs_path = FLAGS_memfs_malloc_path
      + "." + pid;

    int hugetlb_fd = open(hugetlbfs_path.c_str(), O_RDWR | O_CREAT | O_EXCL,
                          0600);
    CHECK_ERR(hugetlb_fd);
    // Cleanup memory on process exit
    CHECK_ERR(unlink(hugetlbfs_path.c_str()));

    // Use fstatfs to figure out the default page size for memfs
    struct statfs sfs;
    CHECK_ERR(fstatfs(hugetlb_fd, &sfs));
    int64 page_size = sfs.f_bsize;

    SysAllocator *alloc = new HugetlbSysAllocator(hugetlb_fd, page_size);
    // Register ourselves with tcmalloc
    RegisterSystemAllocator(alloc, 0);
  }
}

REGISTER_MODULE_INITIALIZER(memfs_malloc, { InitSystemAllocator(); });

#endif   /* ifdef __linux */