When will G1 GC trigger initial-mark besides IHOP

[Bernd Eckenfels]

Hello Roy,

here you find something about the G1 Evacuation Pause (full young mode)

https://plumbr.io/handbook/garbage-collection-algorithms-implementations/g1/evacuation-pause-fully-young

This in addition to the meta space resizing Thomas described.

Gruss
Bernd


--
http://bernd.eckenfels.net
________________________________
Von: hotspot-gc-use <hotspot-gc-use-bounces at openjdk.java.net> im Auftrag von Thomas Schatzl <thomas.schatzl at oracle.com>
Gesendet: Donnerstag, Januar 30, 2020 5:36 PM
An: hotspot-gc-use at openjdk.java.net
Betreff: Re: When will G1 GC trigger initial-mark besides IHOP

Hi,

On 30.01.20 16:51, Roy Zhang wrote:
> Dear JVM experts,
>
> I set -XX:InitiatingHeapOccupancyPercent=70 in JDK8 (no adaptive IHOP
> feature), but I found there are two initial-mark phase at the beginning
> of JVM start when HeapOccupancyPercent is far less than 70%, is there
> any other factor which will trigger G1 GC initial mark phase? Thanks in
> advance!
>
> *Excerpt of GC log:*
> 2020-01-22T03:58:14.227+0000: 3.158: [GC pause (Metadata GC Threshold)
> (young) (initial-mark), 0.1583711 secs]
> [Eden: 1056.0M(81920.0M)->0.0B(81184.0M) Survivors: 0.0B->736.0M Heap:
> 1472.0M(160.0G)->1179.5M(160.0G)]
> 2020-01-22T04:13:07.073+0000: 896.004: [GC pause (G1 Evacuation Pause)
> (young) (initial-mark), 3.8512514 secs]
> [Eden: 81184.0M(81184.0M)->0.0B(71904.0M) Survivors: 736.0M->10016.0M
> Heap: 83643.5M(160.0G)->11744.0M(160.0G)]
>

   the log message before the "initial mark" gc tells you - when the
Metaspace is about to get full to try to unload data in it (e.g. Class
data).

I.e. the condition is either:
- Java heap gets too full
- Metaspace gets too full

Thanks,
   Thomas
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