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-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()