Reduce WriteAll allocs

[klauspost]

Motivation and Context

WriteAll saw 127GB allocs in a 5 minute timeframe for 4MiB buffers used by io.CopyBuffer even if they are pooled.

Since all writers appear to write byte buffers, just send those instead and write directly.

The files are opened through the os package so they have no special properties anyway.

This removes the alloc and copy for each operation.

REST sends content length so a precise alloc can be made.

This should probably be released alongside an API upgrade since we now send and rely on content-length.

How to test this PR?

Operation should be covered by existing tests.

Types of changes

• Feature

[minio-trusted]

Mint Automation

Test	Result
mint-large-bucket.sh	✔️
mint-fs.sh	✔️
mint-gateway-s3.sh	✔️
mint-erasure.sh	✔️
mint-dist-erasure.sh	✔️
mint-zoned.sh	✔️
mint-gateway-nas.sh	✔️
mint-gateway-azure.sh	❌ more...

10810-da5cb01/mint-gateway-azure.sh.log:

Running with
SERVER_ENDPOINT:      minio-dev7.minio.io:32660
ACCESS_KEY:           minioazure
SECRET_KEY:           ***REDACTED***
ENABLE_HTTPS:         0
SERVER_REGION:        us-east-1
MINT_DATA_DIR:        /mint/data
MINT_MODE:            full
ENABLE_VIRTUAL_STYLE: 0

To get logs, run 'docker cp d9f8415fc809:/mint/log /tmp/mint-logs'

(1/15) Running aws-sdk-go tests ... done in 9 seconds
(2/15) Running aws-sdk-java tests ... done in 1 seconds
(3/15) Running aws-sdk-php tests ... done in 3 minutes and 31 seconds
(4/15) Running aws-sdk-ruby tests ... done in 20 seconds
(5/15) Running awscli tests ... done in 3 minutes and 1 seconds
(6/15) Running healthcheck tests ... done in 1 seconds
(7/15) Running mc tests ... done in 3 minutes and 26 seconds
(8/15) Running minio-dotnet tests ... done in 1 minutes and 40 seconds
(9/15) Running minio-go tests ... FAILED in 1 minutes and 50 seconds
{
  "args": {
    "bucketName": "minio-go-test-6xypjsz3ksmakh1h",
    "objectName": "test-object",
    "opts": "",
    "size": -1
  },
  "duration": 1086,
  "function": "PutObject(bucketName, objectName, reader,size,opts)",
  "message": "Unexpected size",
  "name": "minio-go: testPutObjectStreaming",
  "status": "FAIL"
}
(9/15) Running minio-java tests ... done in 10 minutes and 45 seconds
(10/15) Running minio-js tests ... FAILED in 46 seconds
{
  "name": "minio-js",
  "function": "\"after all\" hook in \"functional tests\"",
  "duration": 79,
  "status": "FAIL",
  "error": "S3Error: The bucket you tried to delete is not empty at Object.parseError (node_modules/minio/dist/main/xml-parsers.js:86:11) at /mint/run/core/minio-js/node_modules/minio/dist/main/transformers.js:156:22 at DestroyableTransform._flush (node_modules/minio/dist/main/transformers.js:80:10) at DestroyableTransform.prefinish (node_modules/readable-stream/lib/_stream_transform.js:129:10) at prefinish (node_modules/readable-stream/lib/_stream_writable.js:611:14) at finishMaybe (node_modules/readable-stream/lib/_stream_writable.js:620:5) at endWritable (node_modules/readable-stream/lib/_stream_writable.js:643:3) at DestroyableTransform.Writable.end (node_modules/readable-stream/lib/_stream_writable.js:571:22) at IncomingMessage.onend (_stream_readable.js:682:10) at endReadableNT (_stream_readable.js:1252:12) at processTicksAndRejections (internal/process/task_queues.js:80:21)"
}
(10/15) Running minio-py tests ... done in 20 minutes and 8 seconds
(11/15) Running s3cmd tests ... done in 2 minutes and 28 seconds
(12/15) Running s3select tests ... done in 39 seconds
(13/15) Running security tests ... done in 1 seconds

Executed 13 out of 15 tests successfully.

Deleting image on docker hub
Deleting image locally