linux - Linux 中的 vm.overcommit_ratio 是什么？

Question

这是我当前的设置:

vm.overcommit_ratio = 50 (default)
vm.overcommit_memory = 2

和当前内存使用情况:

[localhost~]$ free -g
             total       used       free     shared    buffers     cached
Mem:            47         46          0          0          0         45
-/+ buffers/cache:          1         45
Swap:           47          0         47

根据 documentation我的理解是:

vm.overcommit_memory = 2 不允许过量使用内存超过 50% 的 RAM (因为 vm.overcommit_ratio 是 50) 但我仍然可以看到当前的内存使用情况是 47 GB 中的 46 GB。

我是不是误会了什么？

Answer 1

我相信 vm.overcommit_memory 的默认值是 0 而不是 2。overcommit_ratio 是否只与模式 2 相关？我想是的，但我不完全确定。

来自 https://www.kernel.org/doc/Documentation/vm/overcommit-accounting

0 - Heuristic overcommit handling. Obvious overcommits of addressspace are refused. Used for a typical system. It ensures a seriouslywild allocation fails while allowing overcommit to reduce swapusage. root is allowed to allocate slightly more memory in thismode. This is the default.

1 - Always overcommit. Appropriate for some scientific applications.Classic example is code using sparse arrays and just relying on thevirtual memory consisting almost entirely of zero pages.

2 - Don't overcommit. The total address space commit for the systemis not permitted to exceed swap + a configurable amount (default is50%) of physical RAM. Depending on the amount you use, in mostsituations this means a process will not be killed while accessingpages but will receive errors on memory allocation as appropriate.

而不是 free -g 我假设四舍五入为零，你可能想使用 free -m 或只是 free 是更精确。

这可能也很有趣:

cat/proc/meminfo|grep 提交