diagnostics: dotnet-dump is incredibly slow in dumpheap scenario

I’m trying to detect a memory leak in the application. Here is what tool says:

> dumpheap -stat -min 5000
Statistics:
              MT    Count    TotalSize Class Name
00007fa6a019a818        1        22080 System.Collections.Generic.Dictionary`2+Entry[[System.Type, System.Private.CoreLib],[System.Collections.Generic.List`1[[System.Type, System.Private.CoreLib]], System.Private.CoreLib]][]
00007fa6985150a0        1        23020 System.UInt16[]
00007fa6a01a39e0        1        32792 MS.Internal.Xml.Cache.XPathNode[]
00007fa69db666e0        1        32792 System.Collections.Concurrent.ConcurrentQueue`1+Segment+Slot[[System.Buffers.MemoryPoolBlock, Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions]][]
00007fa69ccd1778        1        35840 System.Collections.Concurrent.ConcurrentDictionary`2+Node[[System.Int64, System.Private.CoreLib],[Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.HttpConnectionReference, Microsoft.AspNetCore.Server.Kestrel.Core]][]
00007fa69cbb5ad0        1        35840 UNKNOWN
00007fa6986f9328        1       194312 System.Collections.Generic.HashSet`1+Slot[[System.String, System.Private.CoreLib]][]
00007fa69cbb4ff0        1       196632 UNKNOWN
00007fa696067b40        4       261344 System.Object[]
00007fa69611d910        8       353816 System.Int32[]
00007fa69cbd6be8        1       420480 UNKNOWN
00007fa69611f500        1       420480 System.Collections.Generic.Dictionary`2+Entry[[System.String, System.Private.CoreLib],[System.Object, System.Private.CoreLib]][]
00007fa69810a440        1       524312 System.Collections.Concurrent.ConcurrentQueue`1+Segment+Slot[[System.Threading.IThreadPoolWorkItem, System.Private.CoreLib]][]
00007fa696104d68        1       524312 System.String[]
00007fa6a1b19580       21       688296 UNKNOWN
00007fa6a2244840       36       999264 UNKNOWN
00007fa69fff73d8       14      1182224 UNKNOWN
00007fa69fc2f4e0       25      1940280 UNKNOWN
00007fa69dda3ab0       54      2950416 System.Int16[]
00007fa69632cb10        7      4161704 UNKNOWN
00007fa6961050a0      335     29103136 System.Char[]
00007fa6961014b8     1064     91757068 System.Byte[]
00007fa696100fa0    15422   1358062600 System.String
0000000000c59fa0     8267   1559225242      Free
Total 25269 objects

Not great, but at least I can see that there is a lots of string. Okay, now I’m running

dumpheap -type System.String -min 100

I was awaiting for response for 11 (!) hours and it didn’t print a single line. I had to “cancel command at the user’s request”. So I actually have at least two problems:

1. dump created with createdump has lots of UNKNOWN types in dump. I’ve managed to investigate it with dumpobj and I understood some of them, but the others are just “value type array” and I don’t know what to do with it: there is nothing like da from a windbg. But maybe it’s ok because of symbols since I didn’t use --full flag so I don’t include it in subject and merely point that this problem exists. Creating full dump solves the problem but dump is very large (21gb vs 1.7gb)
2. I just cannot find what eats the memory. Requests don’t get to the end. I’m patient and when I didn’t get result immediately I’ve just left it for the whole night. Now it still didn’t print a single line. On 32gb ram modern CPU hardware.

Configuration

• Is this related to a specific tool? I’m not sure, container is running 2.1 and I cannot change it due to incompatibilities between aspnetcore 2.1 and 3.1
• What OS and version, and what distro if applicable? mcr.microsoft.com/dotnet/core/aspnet:2.1-stretch-slim
• Are you running in any particular type of environment? (e.g. Containers, a cloud scenario, app you are trying to target is a different user) Docker
• Is it a self-contained published application? no

P.S. I wonder if there is an IM to discuss this kind of matter instead of creating issues since I’ve got absolutely no reaction in https://gitter.im/dotnet/csharplang and I don’t know other places.