Use absolute value as lower bound for WriteAmpBasedRateLimiter's limit (

#200)

Make it possible to use a huge value as `rate-bytes-per-sec` without losing the ability to adapt to normal pressure.

Signed-off-by: tabokie <xy.tao@outlook.com>

utilities/rate_limiters/write_amp_based_rate_limiter.cc

@@ -267,9 +267,8 @@ int64_t WriteAmpBasedRateLimiter::CalculateRefillBytesPerPeriod(
 }
 
 Status WriteAmpBasedRateLimiter::Tune() {
- // computed rate limit will be larger than
- // `max_bytes_per_sec_ / kAllowedRangeFactor`
- const int kAllowedRangeFactor = 20;
+ // computed rate limit will be larger than `kMinBytesPerSec`
+ const int64_t kMinBytesPerSec = 10 * 1024 * 1024;
  // high-priority bytes are padded to 20MB
  const int64_t kHighBytesLower = 20 * 1024 * 1024;
  // lower bound for write amplification estimation
@@ -323,7 +322,7 @@ Status WriteAmpBasedRateLimiter::Tune() {
  (ratio + ratio_padding + ratio_delta_) *
  std::max(highpri_bytes_sampler_.GetRecentValue(), kHighBytesLower) / 10;
  new_bytes_per_sec = std::max(
- max_bytes_per_sec_ / kAllowedRangeFactor,
+ kMinBytesPerSec,
  std::min(new_bytes_per_sec,
  max_bytes_per_sec_ - highpri_bytes_sampler_.GetRecentValue()));
  if (new_bytes_per_sec != prev_bytes_per_sec) {