Hello.
I've originally asked this question on StackOverflow:
https://stackoverflow.com/questions/57714300/ho-to-properly-interpret-heapinuse-heapidle-heapreleased-memory-stats-in-gol
So here I will write just a quick summary:
I monitor memory usage of my program to determine memory pressure
conditions when I need to clean up some internal cache to prevent my
program from being killed by OOM killer.
The problem is that (HeapInuse - HeapReleased) value is generally in line
with other system memory stats, but sometimes (after Go runtime starting to
release some used memory to OS), this resulting value is greater than
"used" memory reported by "free" utility:
# Looks BAD: 13488 + 14 + 3631 - 489 = 16644 - more that total system
memoryAvailable: 13488M, HeapAlloc: 10M, HeapInuse: 14M, HeapIdle: 3631M,
HeapReleased: 489M
# It is strange that at this moment HeapIdle - HeapReleased = 3142# > than
2134M of used memory reported by "free" utility.
$ free
total used free shared buff/cache
availableMem: 16123232 2185696 13337632 200 599904
13621988Swap: 73242180 34560 73207620
But, after a while, everything is OK again:
# Looks good: 11815 + 2325 + 1320 = 15460Available: 11815M, HeapAlloc: 2322M,
HeapInuse: 2325M, HeapIdle: 1320M, HeapReleased: 0M
I do not understand from where this additional 1.2G (16644M - 15460M) of
memory comes from. When total sum is around 15,5G everything looks good and
memory stats from Go and from "free" are properly aligned. But when total
sum is aroung 16.6G - they aren't - as total memory size is less than that.
>From where this 1.2G of memory originates?
Used swap size remained the same during the whole test.
Thanks in advance,
Sergey.
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