Memory leak in s3manager.newPartPool

[michele]

Please fill out the sections below to help us address your issue.

Version of AWS SDK for Go?

v1.25.48

Version of Go (go version)?

1.13

What issue did you see?

We recently started uploading some files to S3 and noticed we started leaking like crazy. After running pprof, we noticed 97% of the heap is consumed by github.com/aws/aws-sdk-go/service/s3/s3manager.newPartPool.func1

Steps to reproduce

This is the function we're using to serialize a bunch of objects and upload it to S3:

func (s S3Store) Upload(obj Object) error {
        uploader := s3manager.NewUploaderWithClient(s.svc)
        bts, err := json.Marshal(obj)
        if err != nil {
                return errors.Wrap(err, "S3Store#Upload: couldn't marshal object")
        }
        buf := bytes.NewBuffer(bts)
        params := &s3manager.UploadInput{
                Bucket:      aws.String(s.Bucket),
                Key:         aws.String(obj.Filename()),
                Body:        buf,
                ContentType: aws.String("application/json"),
        }
        _, err = uploader.Upload(params)
        if err != nil {
                return errors.Wrap(err, fmt.Sprintf("couldn't upload file to S3: s3://%s/%s", *params.Bucket, *params.Key))
        }
        return nil
}

s.svc is what's returned by s3.New. When uploading a few thousands objects it can easily eat through 100s of MB of RAM.