Port 126929 to 10.0 - #126977

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JulieLeeMSFT merged 2 commits into
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mangod9:fix/gc-largepages-10.0
Apr 29, 2026
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Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from
mangod9:fix/gc-largepages-10.0

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Fixes#126903

Customer Impact

  • Customer reported
  • Found internally

GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.

Regression

  • Yes
  • No

This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level
decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.

Testing

The fix was validated by the customer against their production workload.

Risk

Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11

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Pull request overview

Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.

Changes:

  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.

Comment threadsrc/coreclr/gc/gc.cpp
This was referenced Apr 16, 2026
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@BenV

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?

So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.

@BenV

BenV commented Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?

So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.

Yes, so far so good on the production test, will keep you posted if we run into anything on that front.

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ok will work on getting this approved for back port. Thanks!

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@mangod9mangod9 added the Servicing-consider Issue for next servicing release review label Apr 28, 2026
@JulieLeeMSFTJulieLeeMSFT added Servicing-approved Approved for servicing release and removed Servicing-consider Issue for next servicing release review labels Apr 28, 2026
@JulieLeeMSFTJulieLeeMSFT added this to the 10.0.x milestone Apr 28, 2026
@rbhandarbhanda modified the milestones: 10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.

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JulieLeeMSFT merged commit 5713889 into dotnet:release/10.0Apr 29, 2026
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@BenV, this is now merged so should be included in June servicing.

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@BenV, this is now merged so should be included in June servicing.

Excellent, thanks again for all the help!

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
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Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
@mangod9
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
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Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
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ok will work on getting this approved for back port. Thanks!
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added this to the 10.0.x milestone
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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, 'i');
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
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@mangod9
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Apr 16, 2026•

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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
@mangod9
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MemberAuthor
@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
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Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
@mangod9
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ok will work on getting this approved for back port. Thanks!
@mangod9
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@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
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modified the milestones:
10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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(function(){
try {
var __m = "*";
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Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Conversation
@mangod9
@mangod9mangod9
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Apr 16, 2026•

edited

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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
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ok will work on getting this approved for back port. Thanks!
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@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Apr 28, 2026
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modified the milestones:
10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
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ok will work on getting this approved for back port. Thanks!
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added this to the 10.0.x milestone
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10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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merged commit 5713889
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
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@mangod9
@mangod9mangod9
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Apr 16, 2026•

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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
@mangod9
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
BenV
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Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
@mangod9
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ok will work on getting this approved for back port. Thanks!
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Apr 28, 2026
@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Apr 28, 2026
@rbhandarbhanda
modified the milestones:
10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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merged commit 5713889
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Port 126929 to 10.0 - #126977
Merged
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Apr 29, 2026
Merged
Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
dotnet:release/10.0from 
mangod9:fix/gc-largepages-10.0
Conversation
@mangod9
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commented
Apr 16, 2026•

edited

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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

This was referenced Apr 16, 2026

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@BenV
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
@mangod9
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commented
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MemberAuthor
@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
@BenV
BenV
commented
Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
@mangod9
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ok will work on getting this approved for back port. Thanks!
@mangod9
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added
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added

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and removed

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Apr 28, 2026
@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Apr 28, 2026
@rbhandarbhanda
modified the milestones:
10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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merged commit 5713889
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dotnet:release/10.0Apr 29, 2026

107 of 108 checks passed

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@BenV, this is now merged so should be included in June servicing.
@BenV
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Apr 29, 2026

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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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Port 126929 to 10.0 - #126977
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JulieLeeMSFT merged 2 commits into
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mangod9:fix/gc-largepages-10.0
Apr 29, 2026
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Port 126929 to 10.0#126977
JulieLeeMSFT merged 2 commits into
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mangod9:fix/gc-largepages-10.0
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Apr 16, 2026•

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Fixes#126903
Customer Impact
  •  Customer reported
  •  Found internally
GC heap corruption when DOTNET_GCLargePages=1 is enabled on Linux (#126903). . Reproducible by calling GC.Collect(2, GCCollectionMode.Aggressive, true, true) with large pages enabled, but also occurs in normal production workloads without aggressive GC.
Regression
  •  Yes
  •  No
This is a pre-existing bug in the GC's large-page decommit logic. When GCLargePages is enabled, the GC skips OS-level

decommits but still updates bookkeeping as if the decommit succeeded. This causes regions to be reused without being zeroed, leading to heap corruption. The bug has existed since Regions was enabled.
Testing
The fix was validated by the customer against their production workload.
Risk
Low. The fix clears decommitted memory in the large-pages scenario to ensure regions are properly zeroed before reuse. This is a targeted change to the GC's decommit path that only affects GCLargePages=1 configurations. The larger fix#127290 is made in .NET 11
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April 16, 2026 00:23
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Pull request overview
Ports the fix for #126903 to the 10.0 branch by ensuring memory that is logically decommitted while GCLargePages is enabled is also cleared, preventing stale object references from being observed when the region is later reused.
Changes:
  • Extends gc_heap::virtual_decommit with an optional end_of_data parameter to allow clearing memory when OS decommit is a no-op under large pages.
  • In the aggressive-induced GC path, passes heap_segment_used(region) so the GC clears stale reference-containing bytes when shrinking heap_segment_committed.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/gc/gcpriv.hUpdates the virtual_decommit declaration to accept an optional end_of_data pointer.
src/coreclr/gc/gc.cppImplements large-page clearing in virtual_decommit and wires end_of_data from distribute_free_regions() for aggressive-induced decommits.
Comment threadsrc/coreclr/gc/gc.cpp

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@BenV
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Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
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Apr 28, 2026

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@mangod9 Thanks again for helping out with this - is this still on track to get merged for the June release? Would it also make sense to backport #127290?
So just checking that your prod test went well too? Current thinking is to back port only the targeted fix.
Yes, so far so good on the production test, will keep you posted if we run into anything on that front.
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ok will work on getting this approved for back port. Thanks!
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added this to the 10.0.x milestone
Apr 28, 2026
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10.0.x, 10.0.9Apr 28, 2026
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@neiljohari, @janvorli, @mangod9, please resolve code review comments.
@JulieLeeMSFT
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@BenV, this is now merged so should be included in June servicing.
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@BenV, this is now merged so should be included in June servicing.
Excellent, thanks again for all the help!
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