fix(uffd): dedupe deferred page faults by ValentaTomas · Pull Request #2864 · e2b-dev/infra

ValentaTomas · 2026-05-29T21:29:33Z

Summary

Deduplicate deferred UFFD faults by address so repeated EAGAINs for the same page do not flood the retry queue or wake loop.

Test plan

Not run; Linux UFFD package depends on Linux cgo types and cannot execute on this macOS host.

cursor · 2026-05-29T21:29:39Z

PR Summary

Low Risk
Small, localized change to deferred fault retry bookkeeping in the Linux sandbox UFFD path, with unit tests and no auth or data-path impact.

Overview
Deferred userfaultfd retries now keep at most one queued fault per page address, so many threads faulting the same page after EAGAIN no longer multiply entries in the retry queue and poll wake loop. When a later fault for that page is a write, the kept entry is upgraded to a write fault so the retry resolves the page dirty instead of relying on a follow-up WP fault.

^{Reviewed by Cursor Bugbot for commit 2b7e091. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-05-29T21:30:34Z

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
2707	2	2705	5

View the full list of 2 ❄️ flaky test(s)

github.com/e2b-dev/infra/tests/integration/internal/tests/orchestrator::TestSandboxMemoryIntegrity

Flake rate in main: 57.71% (Passed 740 times, Failed 1010 times)

Stack Traces | 69s run time

=== RUN   TestSandboxMemoryIntegrity
=== PAUSE TestSandboxMemoryIntegrity
=== CONT  TestSandboxMemoryIntegrity
    sandbox_memory_integrity_test.go:27: Build completed successfully
--- FAIL: TestSandboxMemoryIntegrity (68.98s)

github.com/e2b-dev/infra/tests/integration/internal/tests/orchestrator::TestSandboxMemoryIntegrity/tmpfs_hash

Flake rate in main: 57.83% (Passed 730 times, Failed 1001 times)

Stack Traces | 199s run time

=== RUN   TestSandboxMemoryIntegrity/tmpfs_hash
=== PAUSE TestSandboxMemoryIntegrity/tmpfs_hash
=== CONT  TestSandboxMemoryIntegrity/tmpfs_hash
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{start:{pid:1259}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stdout:"Total memory: 985 MB\n"}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stdout:"Used memory before tmpfs mount: 193 MB\n"}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stdout:"Free memory before tmpfs mount: 791 MB\nMemory to use in integrity test (60% of free, min 64MB): 474 MB\n"}}
Executing command bash in sandbox iv6onr1rvybod2v97dlph (user: root)
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stderr:"474+0 records in\n474+0 records out\n497025024 bytes (497 MB, 474 MiB) copied, 2.16223 s, 230 MB/s\n"}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stdout:"Used memory after tmpfs mount and file fill: 669 MB\n"}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{data:{stderr:"\tCommand being timed: \"dd if=/dev/urandom of=/mnt/testfile bs=1M count=474\"\n\tUser time (seconds): 0.00\n\tSystem time (seconds): 1.99\n\tPercent of CPU this job got: 91%\n\tElapsed (wall clock) time (h:mm:ss or m:ss): 0:02.16\n\tAverage shared text size (kbytes): 0\n\tAverage unshared data size (kbytes): 0\n\tAverage stack size (kbytes): 0\n\tAverage total size (kbytes): 0\n\tMaximum resident set size (kbytes): 2636\n\tAverage resident set size (kbytes): 0\n\tMajor (requiring I/O) page faults: 3\n\tMinor (reclaiming a frame) page faults: 344\n\tVoluntary context switches: 4\n\tInvoluntary context switches: 45\n\tSwaps: 0\n\tFile system inputs: 176\n\tFile system outputs: 0\n\tSocket messages sent: 0\n\tSocket messages received: 0\n\tSignals delivered: 0\n\tPage size (bytes): 4096\n\tExit status: 0\n"}}
    sandbox_memory_integrity_test.go:70: Command [bash] output: event:{end:{exited:true  status:"exit status 0"}}
    sandbox_memory_integrity_test.go:70: Command [bash] completed successfully in sandbox ihllff4vv3buv3t5d7ky1
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
    sandbox_memory_integrity_test.go:80: Command [bash] output: event:{start:{pid:1275}}
Executing command bash in sandbox i3j7ic510elbcxuk4gsup (user: root)
    sandbox_memory_integrity_test.go:80: Command [bash] output: event:{data:{stdout:"76a021f37a9659849c0e0c3697177da8237a2e38edb2d04d66382f4b625c6d16\n"}}
    sandbox_memory_integrity_test.go:80: Command [bash] output: event:{end:{exited:true  status:"exit status 0"}}
    sandbox_memory_integrity_test.go:80: Command [bash] completed successfully in sandbox ihllff4vv3buv3t5d7ky1
    sandbox_memory_integrity_test.go:80: Command [bash] output: event:{start:{pid:1278}}
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
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Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
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Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
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Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
Executing command bash in sandbox ihllff4vv3buv3t5d7ky1 (user: root)
    sandbox_memory_integrity_test.go:110: 
        	Error Trace:	.../tests/orchestrator/sandbox_memory_integrity_test.go:81
        	            				.../hostedtoolcache/go/1.26.3.../src/runtime/asm_amd64.s:1771
        	Error:      	Received unexpected error:
        	            	failed to execute command bash in sandbox ihllff4vv3buv3t5d7ky1: unavailable: HTTP status 502 Bad Gateway
    sandbox_memory_integrity_test.go:110: 
        	Error Trace:	.../tests/orchestrator/sandbox_memory_integrity_test.go:78
        	            				.../tests/orchestrator/sandbox_memory_integrity_test.go:110
        	Error:      	Condition never satisfied
        	Test:       	TestSandboxMemoryIntegrity/tmpfs_hash
--- FAIL: TestSandboxMemoryIntegrity/tmpfs_hash (198.86s)

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gemini-code-assist

Code Review

This pull request introduces deduplication of deferred pagefaults by address in the deferredFaults struct to prevent redundant wakeups. It adds a byAddr map to track and deduplicate addresses, updates the Serve loop to only signal wakeups when a new pagefault is successfully deferred, and includes unit tests to verify this behavior. There are no review comments, and no issues were identified in the changes.

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cursor

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Drop the dedupe map after draining so one burst of unique addresses does not retain map capacity for the sandbox lifetime.

Key deferred page faults by page boundary so same-page offsets coalesce before retry.

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Convert the cgo pagefault address to uint64 before page-boundary dedupe.

Round cgo pagefault addresses to the page boundary before deduping deferred retries.

fix(uffd): dedupe deferred page faults

b1824ec

cla-bot Bot added the cla-signed label May 29, 2026

gemini-code-assist Bot reviewed May 29, 2026

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ValentaTomas marked this pull request as ready for review May 29, 2026 22:04

ValentaTomas requested review from dobrac and jakubno as code owners May 29, 2026 22:04

fix(uffd): cast deferred fault addresses

db70cc9

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Comment thread packages/orchestrator/pkg/sandbox/uffd/userfaultfd/deferred.go Outdated

dobrac approved these changes May 30, 2026

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fix(uffd): upgrade deduped deferred fault to write

306359e

cursor Bot reviewed May 31, 2026

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Comment thread packages/orchestrator/pkg/sandbox/uffd/userfaultfd/deferred.go Outdated

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Comment thread packages/orchestrator/pkg/sandbox/uffd/userfaultfd/deferred.go

ValentaTomas added 2 commits May 30, 2026 20:02

fix(uffd): release deferred fault address map on drain

e45c225

Drop the dedupe map after draining so one burst of unique addresses does not retain map capacity for the sandbox lifetime.

fix(uffd): dedupe deferred faults by page

dd691d5

Key deferred page faults by page boundary so same-page offsets coalesce before retry.

chatgpt-codex-connector Bot reviewed May 31, 2026

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Comment thread packages/orchestrator/pkg/sandbox/uffd/userfaultfd/deferred.go Outdated

ValentaTomas added 6 commits May 30, 2026 20:43

fix(uffd): dedupe deferred faults by address

3f35cda

fix(uffd): minimize deferred fault dedup to address-only

2e11f6e

fix(uffd): cast deferred fault address before keying

390e586

Convert the cgo pagefault address to uint64 before page-boundary dedupe.

fix(uffd): dedupe deferred faults by page

6b552c9

Round cgo pagefault addresses to the page boundary before deduping deferred retries.

fix(uffd): drop redundant page-aligned dedup key

509eb58

fix(uffd): upgrade deduped deferred fault to write

2b7e091

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fix(uffd): dedupe deferred page faults#2864

fix(uffd): dedupe deferred page faults#2864
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ValentaTomas commented May 29, 2026

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