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Enable GC Regions on Mac #115251

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42cf430
try enabling regions on Mac again
mangod9 May 2, 2025
e789573
Merge branch 'main' into enable_regions_mac
mangod9 May 7, 2025
5fe5e62
dont enable for iOS and tvOS
mangod9 May 7, 2025
7990cf5
Merge branch 'enable_regions_mac' of http://github.com/mangod9/runtim…
mangod9 May 7, 2025
ff2904d
update binary size due to regions
mangod9 May 8, 2025
c746c16
update comment
mangod9 May 15, 2025
db2b2cb
Merge branch 'main' into enable_regions_mac
mangod9 May 15, 2025
63a230d
make regions_ranage 2x physical_mem for WKS
mangod9 May 21, 2025
a0ee7ec
update reservationSize on iOS
mangod9 May 22, 2025
47ba0b7
fixing typo
mangod9 May 22, 2025
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10 changes: 10 additions & 0 deletions src/coreclr/gc/gc.cpp
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Expand Up @@ -49318,8 +49318,18 @@ HRESULT GCHeap::Initialize()
}
else
{
#ifdef MULTIPLE_HEAPS
// 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 defined(TARGET_IOS) || defined(TARGET_TVOS)
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Update the comment?

// 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);
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@mangod9 mangod9 May 22, 2025 •
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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?

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How much is physical_mem / 4 in absolute numbers?

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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.

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@jkotas jkotas May 23, 2025 •
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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.

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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.

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@jkotas jkotas May 23, 2025 •
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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.

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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?

#else // TARGET_IOS && TARGET_TVOS
// 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 = (size_t)(2 * gc_heap::total_physical_mem);
#endif // TARGET_IOS && TARGET_TVOS
#endif // MUTLIPLE_HEAPS
}
size_t virtual_mem_limit = GCToOSInterface::GetVirtualMemoryLimit();
gc_heap::regions_range = min(gc_heap::regions_range, virtual_mem_limit/2);
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4 changes: 2 additions & 2 deletions src/coreclr/gc/gcpriv.h
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Expand Up @@ -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
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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.

// For SunOS or illumos this is temporary, until we can add MAP_PRIVATE
// to the mmap() calls in unix/gcenv.unix.cpp More details here:
// https://github.com/dotnet/runtime/issues/104211
#if defined (HOST_64BIT) && !defined (BUILD_AS_STANDALONE) && !defined(__APPLE__) && !defined(__sun)
#if defined (HOST_64BIT) && !defined (BUILD_AS_STANDALONE) && !defined(__sun)
#define USE_REGIONS
#endif //HOST_64BIT && BUILD_AS_STANDALONE && !__APPLE__

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2 changes: 1 addition & 1 deletion src/tests/nativeaot/SmokeTests/HardwareIntrinsics/Program.cs
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Expand Up @@ -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
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what's the reason for this change?

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


if (fileSize < lowerBound || fileSize > upperBound)
{
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