Enable GC Regions on Mac #115251

mangod9 · 2025-05-02T19:52:09Z

Regions will be enabled for macOS, but still disabled for iOS and tvOS builds for now (will investigate the test failures on those platforms and try to enable in subsequent PRs).

Copilot

Pull Request Overview

This pull request attempts to re-enable regions on Mac by modifying the preprocessor condition.

Removed the APPLE exclusion from the condition for defining USE_REGIONS
Adjusted the code responsible for enabling regions on 64-bit systems

src/coreclr/gc/gcpriv.h

dotnet-policy-service · 2025-05-02T19:52:43Z

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jkotas · 2025-05-02T20:37:56Z

It is ok to try and the CI may even pass if the run does not happen to generate crash dump along the way. We need a positive confirmation that enabling regions GC won't kill post-mortem diagnostic on mac. Have we done anything to resolve the problem with prohibitively large crash dumps on mac?

mangod9 · 2025-05-02T21:06:51Z

the last time we looked we werent able to repro the large dumps locally. Believe @janvorli had tried it too, given lower priority we never investigated it completely. Hoping we get to root cause this time around.

mangod9 · 2025-05-07T15:59:34Z

I have validated that with large memory reservation size with regions the dump generated on MacOS is about 100mb larger (so it's only about 2% more) -- not order of magnitude larger we thought it would be. Need to figure out failures in iOS/tvOS NativeAOT failures before we can enable.

…into enable_regions_mac

mangod9 · 2025-05-08T04:33:00Z

excluding iOS and tvOS seems to get things to work. Will need to figure out if reducing the reservation size would get regions to work on those platforms too.

Maoni0 · 2025-05-15T07:04:29Z

src/coreclr/gc/gcpriv.h

@@ -140,11 +140,11 @@ inline void FATAL_GC_ERROR()
 //
 // This means any empty regions can be freely used for any generation. For
 // Server GC we will balance regions between heaps.
-// For now disable regions for standalone GC and macOS builds
+// For now disable regions for standalone GC and iOS and tvOS builds


Suggested change

// For now disable regions for standalone GC and iOS and tvOS builds

// For now disable regions for iOS and tvOS builds

might as well take this opportunity to fix this comment since we do have a standalone GC with regions.

Maoni0 · 2025-05-15T07:04:58Z

src/tests/nativeaot/SmokeTests/HardwareIntrinsics/Program.cs

@@ -22,7 +22,7 @@ static int Main()

        long lowerBound, upperBound;
        lowerBound = 1200 * 1024; // ~1.2 MB
-        upperBound = 1600 * 1024; // ~1.6 MB
+        upperBound = 1700 * 1024; // ~1.7 MB


what's the reason for this change?

this test checks for size_on_disk of the test binary. Regions adds more code which puts it over the test threshold.

jkotas · 2025-05-15T13:43:53Z

disabled for iOS and tvOS builds for now (will investigate the test failures on those platforms and try to enable in subsequent PRs).

I do not think this is a good plan. Analyzing failures and debugging iOS/tvOS is much harder than debugging macOS. If a segments-specific issue gets introduced in the meantime, it will be a lot harder and much more time consuming to diagnose it.

mangod9 · 2025-05-15T14:40:02Z

ok, will investigate failures and enable for them too.

filipnavara · 2025-05-22T10:00:48Z

src/coreclr/gc/gc.cpp

            // If no hard_limit is configured the reservation size is min of 1/2 GetVirtualMemoryLimit() or max of 256Gb or 2x physical limit.
            gc_heap::regions_range = max((size_t)256 * 1024 * 1024 * 1024, (size_t)(2 * gc_heap::total_physical_mem));
+#else // MUTLIPLE_HEAPS
+            // If no hard_limit is configured the reservation size is min of 1/2 GetVirtualMemoryLimit() or max of 256Gb or 2x physical limit.


Update the comment?

on my local testing looks like reservation of 1/4th of physical memory seems to succeed.

mangod9 · 2025-05-22T23:46:58Z

src/coreclr/gc/gc.cpp

+#else // MUTLIPLE_HEAPS
+#if defined(TARGET_IOS) || defined(TARGET_TVOS)
+            // On iOS and tvOS only try to reserve 1/4 of physical memory
+            gc_heap::regions_range = (size_t)(gc_heap::total_physical_mem / 4);


physical_mem / 4 was required to get the iOS sample to work on my device. That works for CI as well. Haven't found any specific guidance online around specific policy here. CoPilot claims 2x to 4x reservation should be allowed on iOS but that doesn't seem to be the case. @vitek-karas, any guidance here?

How much is physical_mem / 4 in absolute numbers?

https://alwaysprocessing.blog/2022/02/20/size-matters is a great description of iOS virtual address space limitations. The available address space is limited and precious, very similar to the situation on 32-bit OSes.

physical_mem / 4

I expect that this number will be even lower for real world apps that load a bunch of libraries and occupy/fragment the address space further. iOS does some address space randomization, so the exact size of the largest block of memory that we are able to reserve will differ from run to run. And if we reserve too big of a block, other parts of the app may run into out of memory errors while there is a plenty of memory available.

I think it means that we should treat iOS as 32-bit OS when it comes to memory reservations. Unless we figure out how to make regions GC work well on 32-bit OSes, we should probably keep using segments GC on iOS, maybe even lower default segment size to make it work more like 32-bit OS.

How much is physical_mem / 4 in absolute numbers?

on my iPhone 16 Pro its 2gb (8gb total physical memory). Agree that we should keep iOS on segments for now.

Then the question is whether we want to keep macOS on segments too to get a real-world test coverage for segments on 64-bit architectures in an easy to diagnose environment.

Don't have a strong preference since Mac has always been on segments. However, given the overall memory policy differences do we feel that iOS specific issues would be repro-able on Mac to help with diagnosing?

mangod9 · 2025-06-11T18:14:49Z

closing this PR for now, given the challenges with iOS probably reasonable to leave Apple platforms on segments for now. We will evaluate again if there is a strong case of regions helping on MacOS.

try enabling regions on Mac again

42cf430

Copilot AI review requested due to automatic review settings May 2, 2025 19:52

ghost added the area-GC-coreclr label May 2, 2025

mangod9 marked this pull request as draft May 2, 2025 19:52

dotnet-policy-service bot assigned mangod9 May 2, 2025

mangod9 added the NO-MERGE The PR is not ready for merge yet (see discussion for detailed reasons) label May 2, 2025

Copilot AI reviewed May 2, 2025

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src/coreclr/gc/gcpriv.h Show resolved Hide resolved

mangod9 added 3 commits May 7, 2025 09:12

Merge branch 'main' into enable_regions_mac

e789573

dont enable for iOS and tvOS

5fe5e62

Merge branch 'enable_regions_mac' of http://github.com/mangod9/runtime …

7990cf5

…into enable_regions_mac

build-analysis bot mentioned this pull request May 8, 2025

SmtpClientSendMailTest_SendAsync.MultipleRecipients_Failure_All test failure #115070

Closed

update binary size due to regions

ff2904d

build-analysis bot mentioned this pull request May 8, 2025

CI flakiness: mono interpreter build getting killed #114123

Open

mangod9 added 2 commits May 14, 2025 21:58

update comment

c746c16

Merge branch 'main' into enable_regions_mac

db2b2cb

mangod9 marked this pull request as ready for review May 15, 2025 05:00

mangod9 changed the title ~~[DRAFT] try enabling regions on Mac again~~ Enable GC Regions on Mac May 15, 2025

mangod9 requested a review from Maoni0 May 15, 2025 05:01

Maoni0 reviewed May 15, 2025

View reviewed changes

This was referenced May 15, 2025

[wasm][debugger] Debugger tests disabled #89409

Open

The active test run was aborted. Reason: Test host process crashed dotnet/dnceng#451

Open

make regions_ranage 2x physical_mem for WKS

63a230d

filipnavara reviewed May 22, 2025

View reviewed changes

mangod9 added 2 commits May 22, 2025 13:05

update reservationSize on iOS

a0ee7ec

on my local testing looks like reservation of 1/4th of physical memory seems to succeed.

fixing typo

47ba0b7

mangod9 commented May 22, 2025

View reviewed changes

build-analysis bot mentioned this pull request May 23, 2025

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

Open

3 tasks

jkotas mentioned this pull request May 31, 2025

enable regions for MacOS #98521

Closed

mangod9 closed this Jun 11, 2025

	// For now disable regions for standalone GC and iOS and tvOS builds
	// For now disable regions for iOS and tvOS builds

Enable GC Regions on Mac #115251

Enable GC Regions on Mac #115251

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