Linux 内核参数：extra_free_kbytes

源码基于：Linux 5.4

针对节点 /proc/sys/vm/extra_free_kbytes

0. 官方描述

/Documentation/admin-guide/sysctl/vm.rst

This parameter tells the VM to keep extra free memory between the threshold
where background reclaim (kswapd) kicks in, and the threshold where direct
reclaim (by allocating processes) kicks in.

This is useful for workloads that require low latency memory allocations
and have a bounded burstiness in memory allocations, for example a
realtime application that receives and transmits network traffic
(causing in-kernel memory allocations) with a maximum total message burst
size of 200MB may need 200MB of extra free memory to avoid direct reclaim
related latencies.

在后台回收和直接回收发生的时候告诉 VM 保留额外的空闲内存。这对于需要低延迟内存分配和内存分配中有限制的突发的工作负载非常有用。例如，一个接收和传输网络流量(导致内核内内存分配) 的实时应用程序，其最大总消息突发大小为200MB&#