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rate limit calls to posix_fadvise()

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There can be a large kernel overhead involved in POSIX_FADV_DONTNEED.
There is no point in calling this per item logged, so rate limit
to at most once per 2MiB written.

With a simple test program that logs 100K items at WARNING level:

Before:

  $ time strace -c -e fadvise64 log.test \
    -log_dir=/dev/shm -logtofiles=true -logtostderr=false
  % time     seconds  usecs/call     calls    errors syscall
  ------ ----------- ----------- --------- --------- ----------------
  100.00   12.522509         125     99957           fadvise64
  ------ ----------- ----------- --------- --------- ----------------
  real    0m52.671s
  user    0m2.194s
  sys     0m44.022s

After:

  $ time strace -c -e fadvise64 log.test \
    -log_dir=/dev/shm -logtofiles=true -logtostderr=false

  % time     seconds  usecs/call     calls    errors syscall
  ------ ----------- ----------- --------- --------- ----------------
  100.00    0.000759         152         5           fadvise64
  ------ ----------- ----------- --------- --------- ----------------
  real    0m4.206s
  user    0m1.436s
  sys     0m3.153s

Fixes issue #84
This commit is contained in:
Pádraig Brady 2016-12-09 19:45:34 +00:00
parent b6a5e0524c
commit dacd296796
1 changed files with 14 additions and 11 deletions
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25
src/logging.cc
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@ -114,11 +114,6 @@ GLOG_DEFINE_bool(drop_log_memory, true, "Drop in-memory buffers of log contents.
"Logs can grow very quickly and they are rarely read before they "
"need to be evicted from memory. Instead, drop them from memory "
"as soon as they are flushed to disk.");
_START_GOOGLE_NAMESPACE_
namespace logging {
static const int64 kPageSize = getpagesize();
}
_END_GOOGLE_NAMESPACE_
#endif
// By default, errors (including fatal errors) get logged to stderr as
@ -438,6 +433,7 @@ class LogFileObject : public base::Logger {
FILE* file_;
LogSeverity severity_;
uint32 bytes_since_flush_;
uint32 dropped_mem_length_;
uint32 file_length_;
unsigned int rollover_attempt_;
int64 next_flush_time_; // cycle count at which to flush log
@ -839,6 +835,7 @@ LogFileObject::LogFileObject(LogSeverity severity,
file_(NULL),
severity_(severity),
bytes_since_flush_(0),
dropped_mem_length_(0),
file_length_(0),
rollover_attempt_(kRolloverAttemptFrequency-1),
next_flush_time_(0) {
@ -976,7 +973,7 @@ void LogFileObject::Write(bool force_flush,
PidHasChanged()) {
if (file_ != NULL) fclose(file_);
file_ = NULL;
file_length_ = bytes_since_flush_ = 0;
file_length_ = bytes_since_flush_ = dropped_mem_length_ = 0;
rollover_attempt_ = kRolloverAttemptFrequency-1;
}
@ -1116,11 +1113,17 @@ void LogFileObject::Write(bool force_flush,
(CycleClock_Now() >= next_flush_time_) ) {
FlushUnlocked();
#ifdef OS_LINUX
if (FLAGS_drop_log_memory) {
if (file_length_ >= logging::kPageSize) {
// don't evict the most recent page
uint32 len = file_length_ & ~(logging::kPageSize - 1);
posix_fadvise(fileno(file_), 0, len, POSIX_FADV_DONTNEED);
// Only consider files >= 3MiB
if (FLAGS_drop_log_memory && file_length_ >= (3 << 20)) {
// Don't evict the most recent 1-2MiB so as not to impact a tailer
// of the log file and to avoid page rounding issue on linux < 4.7
uint32 total_drop_length = (file_length_ & ~((1 << 20) - 1)) - (1 << 20);
uint32 this_drop_length = total_drop_length - dropped_mem_length_;
if (this_drop_length >= (2 << 20)) {
// Only advise when >= 2MiB to drop
posix_fadvise(fileno(file_), dropped_mem_length_, this_drop_length,
POSIX_FADV_DONTNEED);
dropped_mem_length_ = total_drop_length;
}
}
#endif