proc/meminfo新增的 MemAvailable

An estimate of how much memory is available for starting new applications, without swapping. Calculated from MemFree, SReclaimable, the size of the file LRU lists, and the low watermarks in each zone.

The estimate takes into account that the system needs some page cache to function well, and that not all reclaimable slab will be reclaimable, due to items being in use. The impact of those factors will vary from system to system.

https://blog.famzah.net/2014/09/24/memavailable-metric-for-linux-kernels-before-3-14-in-procmeminfo/

大概意思：

估算在準備啟動一個新程式時所需要的可用記憶體的，不包括交換區。計算包括空閑記憶體，可回收記憶體，最近最少使用清單的大小以及每個記憶體分區中的低水準标記。

這種估算考慮到系統需要一些頁面緩存給函數，不是所有可回收記憶體都能被回收，因為它們正在被使用着。面對這種情況，每個系統的處理都各不相同。