如果可用記憶體量 (vm.min_free_kbytes) 太低會發生什麼事？

Question

我在核心設定（在 sysctl 中）中遇到了以下參數：

vm.min_free_kbytes

這是無論如何都始終可用的可用記憶體 (RAM) 量。就我而言，我只有 1 GiB 的 RAM，並且此參數設定為大約 64MiB。我認為這相當高，所以到目前為止我將其降低到 8MiB。我不知道是否可以進一步降低它，或者降低到 8MiB 是否會造成任何麻煩，所以問題是如果可用內存量太低會發生什麼？我可以安全地將值降低到 1MiB 嗎？

Answer 1

應該是安全的，但不能保證。來自內核文檔：

min_free_kbytes:

This is used to force the Linux VM to keep a minimum number
of kilobytes free.  The VM uses this number to compute a
watermark[WMARK_MIN] value for each lowmem zone in the system.
Each lowmem zone gets a number of reserved free pages based
proportionally on its size.

Some minimal amount of memory is needed to satisfy PF_MEMALLOC
allocations; if you set this to lower than 1024KB, your system will
become subtly broken, and prone to deadlock under high loads.

Setting this too high will OOM your machine instantly.

本質上，如果將其設為低值，則會出現記憶體分配問題。