Allocation stalls and Page Cache Flushed messages

[Sundara Mohan M]

Hi,
   We started using ZGC and seeing this pattern, Whenever there is
"Allocation Stall" messages before that i see messages like this
...
[2019-10-15T20:02:42.403+0000][71060.202s][info][gc,heap     ] Page Cache
Flushed: 10M requested, 18M(18530M->18512M) flushed
[2019-10-15T20:02:42.582+0000][71060.380s][info][gc,heap     ] Page Cache
Flushed: 12M requested, 18M(17432M->17414M) flushed
[2019-10-15T20:02:42.717+0000][71060.515s][info][gc,heap     ] Page Cache
Flushed: 14M requested, 36M(16632M->16596M) flushed
[2019-10-15T20:02:46.128+0000][71063.927s][info][gc,heap     ] Page Cache
Flushed: 4M requested, 18M(7742M->7724M) flushed
[2019-10-15T20:02:49.716+0000][71067.514s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 28M(2374M->2346M) flushed
[2019-10-15T20:02:49.785+0000][71067.583s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 76M(2346M->2270M) flushed
[2019-10-15T20:02:49.966+0000][71067.765s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2270M->2260M) flushed
[2019-10-15T20:02:50.006+0000][71067.805s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2260M->2250M) flushed
[2019-10-15T20:02:50.018+0000][71067.816s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2250M->2240M) flushed
[2019-10-15T20:02:50.098+0000][71067.896s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2240M->2230M) flushed
[2019-10-15T20:02:50.149+0000][71067.947s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2230M->2220M) flushed
[2019-10-15T20:02:50.198+0000][71067.996s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2220M->2210M) flushed
[2019-10-15T20:02:50.313+0000][71068.111s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 10M(2210M->2200M) flushed
[2019-10-15T20:02:50.327+0000][71068.125s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 26M(2200M->2174M) flushed
[2019-10-15T20:02:50.346+0000][71068.145s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 14M(2174M->2160M) flushed
[2019-10-15T20:02:50.365+0000][71068.163s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 14M(2160M->2146M) flushed
[2019-10-15T20:02:50.371+0000][71068.170s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 8M(2146M->2138M) flushed
[2019-10-15T20:02:50.388+0000][71068.187s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 8M(2138M->2130M) flushed
[2019-10-15T20:02:50.402+0000][71068.201s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 8M(2130M->2122M) flushed
[2019-10-15T20:02:50.529+0000][71068.327s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 8M(2122M->2114M) flushed
[2019-10-15T20:02:50.620+0000][71068.418s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 8M(2114M->2106M) flushed
[2019-10-15T20:02:50.657+0000][71068.455s][info][gc,heap     ] Page Cache
Flushed: 2M requested, 14M(2106M->2092M) flushed
...

1. Any idea what this info message conveys about the system?

2. Our application is allocating object 5X sometimes and Allocation Stall
happens immediately after that. Can ZGC heuristic learn about this increase
and later will it adjust accordingly? Other than increasing memory is there
any other tuning option to consider that will help in this scenario?

I am using JDK12 with 80G heap.

Thanks
Sundar