Full GC notify not raised on Server GC

[hyabean]

Description

In server GC mode and concurrent GC mode, GC.WaitForFullGCApproach() does not return when the remaining memory is reduced to zero.
The code is based on the example from GC.RegisterForFullGCNotification(Int32, Int32) Method (System).

Reproduction Steps

https://github.com/hyabean/GCNotifyTest

Expected behavior

print "GC Notification raised."

Actual behavior

GC.WaitForFullGCApproach() not return even when the remaining memory is 0%.

2025/4/28 19:41:24:Registered for GC notification.
2025/4/28 19:41:25:Gen 2 collection count: 1
2025/4/28 19:41:25:allocCount: 1000000
2025/4/28 19:41:25:allocCount: 2000000
2025/4/28 19:41:25:allocCount: 3000000
2025/4/28 19:41:25:allocCount: 4000000
2025/4/28 19:41:26:allocCount: 5000000
2025/4/28 19:41:26:allocCount: 6000000
2025/4/28 19:41:26:allocCount: 7000000
2025/4/28 19:41:26:Gen 2 collection count: 2
2025/4/28 19:41:27:allocCount: 8000000
2025/4/28 19:41:27:allocCount: 9000000
2025/4/28 19:41:27:allocCount: 10000000
2025/4/28 19:41:27:allocCount: 11000000
2025/4/28 19:41:28:allocCount: 12000000
2025/4/28 19:41:28:allocCount: 13000000
2025/4/28 19:41:28:Gen 2 collection count: 3
2025/4/28 19:41:28:allocCount: 14000000
2025/4/28 19:41:29:allocCount: 15000000
2025/4/28 19:41:29:allocCount: 16000000
2025/4/28 19:41:29:allocCount: 17000000
2025/4/28 19:41:30:allocCount: 18000000
2025/4/28 19:41:30:Gen 2 collection count: 4
2025/4/28 19:41:32:allocCount: 19000000
2025/4/28 19:41:34:allocCount: 20000000
2025/4/28 19:41:35:allocCount: 21000000
2025/4/28 19:41:35:Gen 2 collection count: 5
2025/4/28 19:41:36:allocCount: 22000000
2025/4/28 19:41:39:allocCount: 23000000
2025/4/28 19:41:43:Gen 2 collection count: 6
2025/4/28 19:41:48:allocCount: 24000000
2025/4/28 19:41:50:allocCount: 25000000
2025/4/28 19:41:52:allocCount: 26000000
2025/4/28 19:41:52:allocCount: 27000000
2025/4/28 19:41:53:Gen 2 collection count: 7
2025/4/28 19:42:34:allocCount: 28000000
2025/4/28 19:42:35:allocCount: 29000000
2025/4/28 19:42:36:Gen 2 collection count: 8
2025/4/28 19:43:16:allocCount: 30000000
2025/4/28 19:43:17:allocCount: 31000000
2025/4/28 19:43:18:allocCount: 32000000
2025/4/28 19:43:19:allocCount: 33000000
2025/4/28 19:43:20:Gen 2 collection count: 9
2025/4/28 19:43:20:allocCount: 34000000
2025/4/28 19:44:21:allocCount: 35000000
2025/4/28 19:44:22:allocCount: 36000000
2025/4/28 19:44:22:Gen 2 collection count: 10

PerfViewData_gcnotify3.etl.zip
PerfViewData_gcnotify3.log.txt

Regression?

No response

Known Workarounds

No response

Configuration

.NET 8.0.15
Windows 10 专业版 22H2
x64

Other information

Sometimes, the notification is triggered at the beginning of program execution, but it stops being
after a few tens of seconds. The memory remains full, and both garbage collection (GC) and allocations are very slow.

log triggered at begin.txt

2025/4/28 19:57:45:Registered for GC notification.
2025/4/28 19:57:45:Gen 2 collection count: 1
2025/4/28 19:57:45:allocCount: 1000000
2025/4/28 19:57:45:allocCount: 2000000
2025/4/28 19:57:46:allocCount: 3000000
2025/4/28 19:57:46:allocCount: 4000000
2025/4/28 19:57:46:allocCount: 5000000
2025/4/28 19:57:46:allocCount: 6000000
2025/4/28 19:57:47:allocCount: 7000000
2025/4/28 19:57:47:GC Notification raised.
2025/4/28 19:57:47:Gen 2 collection count: 2
2025/4/28 19:57:47:Redirecting requests.
2025/4/28 19:57:47: bAllocate : False
...
2025/4/28 19:57:47: bAllocate : False
2025/4/28 19:57:47:Induced a collection.
2025/4/28 19:57:47: bAllocate : False
2025/4/28 19:57:47: bAllocate : False
2025/4/28 19:57:47:GC Notification not applicable 2.
2025/4/28 19:57:47: bAllocate : False
2025/4/28 19:57:47:Accepting requests again.
2025/4/28 19:57:47:Gen 2 collection count: 3
2025/4/28 19:57:47:allocCount: 8000000
2025/4/28 19:57:47:allocCount: 9000000
2025/4/28 19:57:47:allocCount: 10000000
2025/4/28 19:57:47:allocCount: 11000000
2025/4/28 19:57:47:allocCount: 12000000
2025/4/28 19:57:47:allocCount: 13000000
2025/4/28 19:57:47:allocCount: 14000000
2025/4/28 19:57:48:GC Notification raised.
2025/4/28 19:57:48:Redirecting requests.
2025/4/28 19:57:48: bAllocate : False
...
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:Induced a collection.
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:GC Notification raised.
2025/4/28 19:57:48:Accepting requests again.
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:Gen 2 collection count: 4
2025/4/28 19:57:48:allocCount: 15000000
2025/4/28 19:57:48:allocCount: 16000000
2025/4/28 19:57:48:allocCount: 17000000
2025/4/28 19:57:48:allocCount: 18000000
2025/4/28 19:57:48:allocCount: 19000000
2025/4/28 19:57:48:GC Notification raised.
2025/4/28 19:57:48:Redirecting requests.
2025/4/28 19:57:48: bAllocate : False
...
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:Induced a collection.
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:GC Notification raised.
2025/4/28 19:57:48:Accepting requests again.
2025/4/28 19:57:48: bAllocate : False
2025/4/28 19:57:48:Gen 2 collection count: 5
2025/4/28 19:57:48:allocCount: 20000000
2025/4/28 19:57:48:allocCount: 21000000
2025/4/28 19:57:48:allocCount: 22000000
2025/4/28 19:57:48:allocCount: 23000000
2025/4/28 19:57:48:allocCount: 24000000
2025/4/28 19:57:48:allocCount: 25000000
2025/4/28 19:57:49:GC Notification raised.
2025/4/28 19:57:49:Redirecting requests.
2025/4/28 19:57:49: bAllocate : False
...
2025/4/28 19:57:49: bAllocate : False
2025/4/28 19:57:49:Induced a collection.
2025/4/28 19:57:49: bAllocate : False
...
2025/4/28 19:57:49: bAllocate : False
2025/4/28 19:57:49:GC Notification raised.
2025/4/28 19:57:49: bAllocate : False
2025/4/28 19:57:49:Accepting requests again.
2025/4/28 19:57:49:Gen 2 collection count: 6
2025/4/28 19:57:49:allocCount: 26000000
2025/4/28 19:57:49:allocCount: 27000000
2025/4/28 19:57:49:allocCount: 28000000
2025/4/28 19:57:49:allocCount: 29000000
2025/4/28 19:57:49:allocCount: 30000000
2025/4/28 19:57:49:allocCount: 31000000
2025/4/28 19:57:49:Gen 2 collection count: 7
2025/4/28 19:57:49:allocCount: 32000000
2025/4/28 19:57:49:allocCount: 33000000
2025/4/28 19:57:50:allocCount: 34000000
2025/4/28 19:57:50:allocCount: 35000000
2025/4/28 19:57:50:allocCount: 36000000
2025/4/28 19:57:50:allocCount: 37000000
2025/4/28 19:57:51:allocCount: 38000000
2025/4/28 19:57:51:allocCount: 39000000
2025/4/28 19:57:52:allocCount: 40000000
2025/4/28 19:57:52:allocCount: 41000000
2025/4/28 19:57:52:allocCount: 42000000
2025/4/28 19:57:53:Gen 2 collection count: 8
2025/4/28 19:57:54:allocCount: 43000000
2025/4/28 19:57:54:Gen 2 collection count: 9
2025/4/28 19:57:56:allocCount: 44000000
2025/4/28 19:57:56:allocCount: 45000000
2025/4/28 19:57:57:Gen 2 collection count: 10
2025/4/28 19:57:57:allocCount: 46000000
2025/4/28 19:57:58:allocCount: 47000000
2025/4/28 19:58:05:allocCount: 48000000
2025/4/28 19:58:07:Gen 2 collection count: 11
2025/4/28 19:58:07:allocCount: 49000000
2025/4/28 19:58:26:allocCount: 50000000
2025/4/28 19:58:27:allocCount: 51000000
2025/4/28 19:58:28:Gen 2 collection count: 12
2025/4/28 19:59:05:allocCount: 52000000
2025/4/28 19:59:05:allocCount: 53000000
2025/4/28 19:59:07:Gen 2 collection count: 13
2025/4/28 19:59:07:allocCount: 54000000
2025/4/28 19:59:46:allocCount: 55000000
2025/4/28 19:59:46:allocCount: 56000000
2025/4/28 19:59:47:Gen 2 collection count: 14
2025/4/28 20:00:42:allocCount: 57000000
2025/4/28 20:00:43:allocCount: 58000000
2025/4/28 20:00:44:Gen 2 collection count: 15
2025/4/28 20:00:44:allocCount: 59000000
2025/4/28 20:01:45:allocCount: 60000000
2025/4/28 20:01:45:allocCount: 61000000
2025/4/28 20:01:46:Gen 2 collection count: 16
2025/4/28 20:02:46:allocCount: 62000000
2025/4/28 20:02:47:allocCount: 63000000
2025/4/28 20:02:48:Gen 2 collection count: 17
2025/4/28 20:02:48:allocCount: 64000000
2025/4/28 20:04:01:allocCount: 65000000
2025/4/28 20:04:02:allocCount: 66000000
2025/4/28 20:04:03:Gen 2 collection count: 18
2025/4/28 20:04:03:allocCount: 67000000
2025/4/28 20:05:23:allocCount: 68000000
2025/4/28 20:05:24:allocCount: 69000000
2025/4/28 20:05:25:Gen 2 collection count: 19
2025/4/28 20:06:50:allocCount: 70000000
2025/4/28 20:06:51:allocCount: 71000000
2025/4/28 20:06:52:allocCount: 72000000
2025/4/28 20:06:53:allocCount: 73000000
2025/4/28 20:06:54:Gen 2 collection count: 20
2025/4/28 20:06:54:allocCount: 74000000
2025/4/28 20:08:35:allocCount: 75000000
2025/4/28 20:08:36:allocCount: 76000000
2025/4/28 20:08:37:allocCount: 77000000
2025/4/28 20:08:37:allocCount: 78000000
2025/4/28 20:08:38:Gen 2 collection count: 21
2025/4/28 20:10:21:allocCount: 79000000
2025/4/28 20:10:21:allocCount: 8000000
2025/4/28 20:10:23:allocCount: 81000000
2025/4/28 20:10:23:Gen 2 collection count: 22

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[hyabean]

There might be an issue with the example of GC.RegisterForFullGCNotification. Because the memory is being referenced by List<byte[]> load, the GC might assume that even performing a FULL GC cannot clean up the heap. If we regularly clear half of the 'load' objects, notification triggering should work as expected.