sorry for being not specific.
my question is:
according to my understanding about memstat ( correct me if I'm wrong)
with GOGC set to 50, I can see from the graph above that GCGoal is ~ 26GB
and heapIdle - heapReleased is how much memory go runtime retain from OS
for later usage, how can it (heapIdle - heapReleased) be 35GB which is 1.3x
GCGoal ?
it seem to me is something stop scavenger from releasing those memory back
to OS.
and by reading the code:
// HeapIdle is bytes in idle (unused) spans.
//
// Idle spans have no objects in them. These spans could be
// (and may already have been) returned to the OS, or they can
// be reused for heap allocations, or they can be reused as
// stack memory.
//
// HeapIdle minus HeapReleased estimates the amount of memory
// that could be returned to the OS, but is being retained by
// the runtime so it can grow the heap without requesting more
// memory from the OS. If this difference is significantly
// larger than the heap size, it indicates there was a recent
// transient spike in live heap size.
HeapIdle uint64
and from mgcscavenge.go:
// That goal is defined as:
// (retainExtraPercent+100) / 100 * (heapGoal / lastHeapGoal) *
last_heap_inuse
it seems (heapIdle - heapReleased) should be like 3GB (which is
retainExtraPercent/100 * heapInUse ~ 10% * 26GB ~ 3GB)
and i'm really confused by this situation that (heapIdle - heapReleased) be
35GB
On Thursday, November 24, 2022 at 3:09:10 PM UTC+8 Amnon wrote:
> Have a look at https://tip.golang.org/doc/gc-guide
>
> and
> https://opensourcelive.withgoogle.com/events/go-day-2022/watch?talk=talk4
>
> On Thursday, 24 November 2022 at 05:08:55 UTC Zhao Weng wrote:
>
>> [image: memory.jpg]
>> memstats show heapIdle - heapReleased > heapAlloc or heapInUse
>>
>> I try to search the code and found the below comment:
>>
>> // HeapIdle is bytes in idle (unused) spans.
>> //
>> // Idle spans have no objects in them. These spans could be
>> // (and may already have been) returned to the OS, or they can
>> // be reused for heap allocations, or they can be reused as
>> // stack memory.
>> //
>> // HeapIdle minus HeapReleased estimates the amount of memory
>> // that could be returned to the OS, but is being retained by
>> // the runtime so it can grow the heap without requesting more
>> // memory from the OS. If this difference is significantly
>> // larger than the heap size, it indicates there was a recent
>> // transient spike in live heap size.
>> HeapIdle uint64
>>
>> and from mgcscavenge.go:
>>
>> // That goal is defined as:
>> // (retainExtraPercent+100) / 100 * (heapGoal / lastHeapGoal) *
>> last_heap_inuse
>>
>> it seem to me heapIdle - heapReleased should be ~ heapInUse * 10%
>>
>> can anybody help me understand this?
>>
>> many thanks!!
>>
>
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