This topic summarizes the features and kernel interfaces supported by Alibaba Cloud Linux 2.
Use of Alibaba Cloud Linux 2 images
The following table describes the operations on Alibaba Cloud Linux 2 images.
|Use Alibaba Cloud Linux 2 images in an on-premises environment||You can download Alibaba Cloud Linux 2 images to and use them on local kernel-based virtual machines (KVMs).|
|Use YUM to perform security updates||You can use YUM to query, check, or install security updates for Alibaba Cloud Linux 2.|
Function interfaces supported by Alibaba Cloud Linux 2
If you have a knowledge about the Linux kernel and want to use Linux kernel features, you can perform operations based on the Alibaba Cloud Linux 2 kernel features and interfaces described in the following table.
|Enable the cgroup writeback feature||Alibaba Cloud Linux 2 supports the cgroup writeback feature for the cgroup v1 kernel interface in the kernel of the 4.19.36-12.al7 or later version. This feature allows you to limit the buffered I/O rate when you use the cgroup v1 kernel interface.|
|Configure the weight-based throttling feature of blk-iocost||Alibaba Cloud Linux 2 provides the weight-based throttling feature (blk-iocost) based on the cost model in the kernel of the 4.19.81-17.al7.x86_64 or later version. This feature improves the weight-based disk throttling feature of the I/O subsystem (blkcg) within a kernel.|
|Enable the PSI feature for cgroup v1||Alibaba Cloud Linux 2 supports the Pressure Stall Information (PSI) feature for the cgroup v1 interface in the kernel of the 4.19.81-17.al7 or later version. This feature allows you to monitor CPUs, memory, and I/O performance.|
|Change the TCP TIME-WAIT timeout period||In the Linux kernel, TCP/IP connections remain in the TIME-WAIT state for 60 seconds. The length of this period cannot be changed. However, in some scenarios such as heavy TCP loads, network performance can be improved if this period is shortened. In this context, Alibaba Cloud Linux 2 provides a kernel interface in the kernel of the 4.19.43-13.al7 or later version to change the length of the TCP TIME-WAIT timeout period.|
|Enhance the monitoring of block I/O throttling||Alibaba Cloud Linux 2 provides interfaces in the kernel of the 4.19.81-17.al7 or later version to better monitor Linux block I/O throttling.|
|Use the JBD2 optimization interface||JBD2 is the kernel thread of ext4 file systems. It often experiences the shadow (BH_Shadow) state during its use, which can affect the system performance. To solve this problem, Alibaba Cloud Linux 2 provides an interface in the kernel of the 4.19.81-17.al7 or later version to optimize JBD2.|
|Create a hard link across project quotas||By default, ext4 file systems have constraints that disallow hard links to be created across project quotas. However, in practice, some scenarios require that hard links be created. Alibaba Cloud Linux 2 provides a custom interface to bypass the constraints of ext4 file systems and create hard links across project quotas.|
|Track I/O latency||Alibaba Cloud Linux 2 optimizes the /proc/diskstats interface that provides raw data for the I/O latency analysis tool iostat. Alibaba Cloud Linux 2 can calculate the durations of read, write, and special I/O (discard) operations on the device side. In addition, Alibaba Cloud Linux 2 provides the bcc tool to track I/O latency.|
|Detect I/O hangs of file systems and block layers||An I/O hang occurs when the system becomes unstable or even goes down due to time-consuming I/O requests. Alibaba Cloud Linux 2 extends the core data structure and provides the feature to locate and detect I/O hangs at a low overhead cost for the system.|
|Memcg global minimum watermark rating||Alibaba Cloud Linux 2 provides the memcg global minimum watermark rating feature. The global wmark_min of resource-consuming tasks is increased to trigger direct memory reclaim. The global minimum watermark of latency-sensitive tasks is decreased to avoid direct memory reclaim. When a resource-consuming task requests a large amount of memory, an increase in the global wmark_min throttles the resources used for the task for a short period to avoid direct memory reclaim for latency-sensitive tasks. After some amount of memory is reclaimed through global kswapd backend reclaim, the resource-consuming task is no longer throttled.|
|Memcg backend asynchronous reclaim||Alibaba Cloud Linux 2 provides the backend asynchronous reclaim feature for memcgs. This feature differs from the global kswapd kernel thread in that it uses the workqueue mechanism instead of a corresponding memcg kswapd kernel thread.|
|Memcg QoS feature of the cgroup v1 interface||The memcg quality of service (QoS) can be used to control locks and limits on memory usage in a memcg. Alibaba Cloud Linux 2 provides the memcg QoS feature supported by the cgroup v1 interface in the kernel of the 4.19.91-18.al7 or later version.|
|Memcg Exstat feature||Alibaba Cloud Linux 2 provides the memcg exstat (Extend/Extra) feature in the kernel of the 4.19.91-18.al7 or later version.|
|TCP-RT configurations||TCP-layer service monitoring (TCP-RT) is supported on Alibaba Cloud Linux 2 with a kernel of the 4.19.91-21.al7 or later version.|