mm: rework MGLRU workingset protection

[raz123]

Feature summary

Port Yu Zhao's MGLRU workingset-protection rework to this page-based Linux 4.19.325 tree. File-descriptor references now use the reference-bit mask, PG_workingset represents the highest tier, and lazy promotion is preserved through generation movement and refault handling.

Source provenance

• Upstream: Yu Zhao, commit 4d5d14a01e2c9091b128fb46e1d07475e9a7bb72
• Subject: mm/mglru: rework workingset protection
• Source license: GPL-2.0
• This is a minimal page-based adaptation; no direct cherry-pick was possible because upstream is folio/newer-kernel based.

Baseline and branch

• Baseline: origin/codex/mglru-bootloop-investigation at 75249a53957b5725b695ca0af6b7825d7ef31c57
• Branch: feature/mglru-workingset-protection-page
• Commit: f4fc226092387263c9101172c70235b8de767cd8

Exact files changed

• include/linux/mm_inline.h
• include/linux/mmzone.h
• mm/swap.c
• mm/vmscan.c
• mm/workingset.c

ABI and userspace behavior

No framework, ROM, device-tree, sepolicy, or userspace changes. Existing MGLRU sysfs/debugfs controls and vmstat interfaces remain in place; only reclaim tier classification and workingset protection behavior change.

Regression gate

1. Testing: MGLRU workingset protection, lazy promotion, deactivation clearing, and page-based refault tier restoration.
2. Baseline diff: zero before edits against the exact integration SHA above.
3. Failure meaning: a failure indicates a porting or reclaim-lifecycle regression, not a mixed feature failure.
4. Isolation: only the five MGLRU MM/header files changed; KSU stayed enabled and no target/device/userspace variables changed.
5. Import/adaptation: yes—clean upstream import intent with minimal page-API adaptations; the target's existing refault-age check was retained as a separate prior experiment.

CI and artifact

• CI run 29380499564
• Result: success; KSU, manual hook, KALLSYMS, SELinux, Binder, image-size, DTB and DTBO gates passed.
• Artifact: flashable-anykernel3 (ID 8329656734)
• Inner flashable ZIP: rp-pocof3_ReSukiSU_b275.zip
• Inner ZIP SHA-256: 843c9b4b0d84b3d3c0bc4958daad0f848ca9365ffa7b44d600d27b5379f30d2c
• Embedded identity: 4.19.325-cip130-st14-aptusitu-perf-b275-gf4fc22609238 #275

Device verification

b275 was validated read-only on alioth: Android 13, boot complete, cold boot, slot _b, and exact kernel identity 4.19.325-cip130-st14-aptusitu-perf-b275-gf4fc22609238 #275 matching CI. CONFIG_LRU_GEN=y, CONFIG_LRU_GEN_ENABLED=y, runtime enabled=0x0003, and live /sys/kernel/debug/lru_gen generation data were present. Refault/reclaim counters were active; oom_kill=0, and the kernel log scan found no panic, Oops, BUG, watchdog, OOM-killer, or RCU-stall match.

Known limitations

This is a page-based 4.19 port, not a direct folio backport. The newer PTE-mapped large-folio follow-up and newer reclaim/writeback series are intentionally excluded. Runtime performance impact is unmeasured.

Next test

Run a controlled b274 versus b275 A/B workload with fixed app set, reboot state, and measurement window. Compare refaults, activation/restoration, reclaim scan/steal, latency, memory pressure, and battery; do not infer performance from lifetime counters alone.