message: nydusd: ensure fscache prefetch size is bigger than 256K
  Ensure fscache prefetch size is bigger than 256K, otherwise it may
  consume to much memory to issue prefetch requests.
diff: @@ -514,6 +514,7 @@ impl FsCacheHandler {
  Some(1) => nydus_api::default_batch_size() as u64,
  Some(s) => s as u64,
  };
  + let size = std::cmp::max(0x4_0000u64, size);
  let blob_size = blob_info.compressed_data_size();
  let count = (blob_size + size - 1) / size;
  let mut blob_req = Vec::with_capacity(count as usize);
  @@ -525,21 +526,15 @@ impl FsCacheHandler {
  len: cmp::min(size, blob_size - pre_offset),
  });
  pre_offset += size;
  - if pre_offset > blob_size {
  + if pre_offset >= blob_size {
  break;
  }
  }
  - info!(
  - "fscache: start to prefetch data for blob {}",
  - blob.blob_id()
  - );
  + let id = blob.blob_id();
  + info!("fscache: start to prefetch data for blob {}", id);
  if let Err(e) = blob.prefetch(blob.clone(), &blob_req, &[]) {
  - warn!(
  - "fscache: failed to prefetch data for blob {}, {}",
  - blob.blob_id(),
  - e
  - );
  + warn!("fscache: failed to prefetch data for blob {}, {}", id, e);
  }
  Ok(())
  @@ -748,8 +743,8 @@ impl FsCacheHandler {
  let file_name = match child.file_name().to_str() {
  Some(n) => n.to_string(),
  None => {
  - env::set_current_dir(&cwd_old)?;
  - return Err(eother!("get file name failed"));
  + warn!("failed to get file name of {}", child.path().display());
  + continue;
  }
  };
  if !path.is_dir() || !file_name.starts_with("Ierofs,") {
  @@ -771,7 +766,7 @@ impl FsCacheHandler {
  res = false;
  }
  Ok(true) => {
  - warn!("blob {} in use, skip!", cookie_path)
  + warn!("blob {} in use, skip!", cookie_path);
  res = false;
  }
  Ok(false) => {
  