warn issues about large block I/O performance for Linux older than 4.0.0 (#14524)

This PR simply adds a warning message when it detects older kernel
versions and warn's them about potential performance issues on this
kernel.

The issue can be seen only with parallel I/O across all drives
on denser setups such as 90 drives or 45 drives per server configurations.

cmd/server-main.go

@@ -448,6 +448,11 @@ func serverMain(ctx *cli.Context) {
 	// Set system resources to maximum.
 	setMaxResources()
 
+	// Verify kernel release and version.
+	if oldLinux() {
+		logger.Info(color.RedBold("WARNING: Detected Linux kernel version older than 4.0.0 release, there are some known potential performance problems with this kernel version. MinIO recommends a minimum of 4.x.x linux kernel version for best performance"))
+	}
+
 	// Configure server.
 	handler, err := configureServerHandler(globalEndpoints)
 	if err != nil {

cmd/server-rlimit.go

@@ -21,10 +21,28 @@ import (
 	"runtime"
 	"runtime/debug"
 
+	"github.com/minio/minio/internal/kernel"
 	"github.com/minio/minio/internal/logger"
 	"github.com/minio/pkg/sys"
 )
 
+func oldLinux() bool {
+	currentKernel, err := kernel.CurrentVersion()
+	if err != nil {
+		// Could not probe the kernel version
+		return false
+	}
+
+	if currentKernel == 0 {
+		// We could not get any valid value return false
+		return false
+	}
+
+	// legacy linux indicator for printing warnings
+	// about older Linux kernels and Go runtime.
+	return currentKernel < kernel.Version(4, 0, 0)
+}
+
 func setMaxResources() (err error) {
 	// Set the Go runtime max threads threshold to 90% of kernel setting.
 	sysMaxThreads, mErr := sys.GetMaxThreads()

cmd/xl-storage.go

@@ -49,11 +49,12 @@ import (
 
 const (
 	nullVersionID = "null"
-	// Really large streams threshold per shard.
-	reallyLargeFileThreshold = 64 * humanize.MiByte // Optimized for HDDs
+	// Largest streams threshold per shard.
+	largestFileThreshold = 64 * humanize.MiByte // Optimized for HDDs
 
 	// Small file threshold below which data accompanies metadata from storage layer.
 	smallFileThreshold = 128 * humanize.KiByte // Optimized for NVMe/SSDs
+
 	// For hardrives it is possible to set this to a lower value to avoid any
 	// spike in latency. But currently we are simply keeping it optimal for SSDs.
 
@@ -1786,8 +1787,8 @@ func (s *xlStorage) CreateFile(ctx context.Context, volume, path string, fileSiz
 	}()
 
 	var bufp *[]byte
-	if fileSize > 0 && fileSize >= reallyLargeFileThreshold {
-		// use a larger 4MiB buffer for really large streams.
+	if fileSize > 0 && fileSize >= largestFileThreshold {
+		// use a larger 4MiB buffer for a really large streams.
 		bufp = xioutil.ODirectPoolXLarge.Get().(*[]byte)
 		defer xioutil.ODirectPoolXLarge.Put(bufp)
 	} else {