linux 关于 swap分区的划分规则

Swap should equal 2x physical RAM for up to 2 GB of physical RAM, and then 1x physical RAM for any amount above 2 GB, but never less than 32 MB.

Using this formula, a system with 2 GB of physical RAM would have 4 GB of , while one with 3 GB of physical RAM would have 5 GB of . Creating a large swap space partition can be especially helpful if you plan to upgrade your RAM at a later time.

Tip
If your partitioning scheme requires a swap partition that is larger than 2 GB, you should create an additional swap partition. For example, if you need 4 GB of swap, you should create two 2 GB swap partitions. If you have 4 GB of RAM, you should create three 2 GB swap partitions. Red Hat Enterprise Linux supports up to 32 swap files.


For systems with really large amounts of RAM (more than 32 GB) you can likely get away with a smaller swap partition (around 1x, or less, of physical RAM).

大概的意思是：
当物理内存小于2G时，swap大小为物理内存的2倍。超过2G的部分，swap大小跟物理内存相等。

也即是，得到如下公式：

x<= 2G的部分, y=2x

x>2G   的部分, y=x

利用这个公式，2G物理内存需要4G swap，而3G物理内存则需要5G swap。如果你打算添加内存的话，创建一个大些的swap区是很有帮助的。

举个例子：如果按照计划，你的swap区超过2G，那么应该创建另外的swap。比如，你需要4G的swap的分区，应该创建2个2G的swap分区。

如果有4G的物理内存，就要6G的swap（根据公式：
2x2GB=4G    1x2GB=2G   上述2个之和。一共6G）
每个swap分区2G。则应该创建3个2G的swap分区。

Redhat EL支持多达32个swap文件。
对于超过32G物理内存的，使用小于等于物理内存容量的swap区会更好。