[PATCH 0/2] mm: batch TLB flushing for dirty folios in vmscan

Zhang Peng via B4 Relay
2026-03-09T08:18:01Z

This series introduces batch TLB flushing optimization for dirty folios
during memory reclaim, aiming to reduce IPI overhead on multi-core systems.

Background
----------
Currently, when performing pageout in memory reclaim, try_to_unmap_flush_dirty()
is called for each dirty folio individually. On multi-core systems, this causes
frequent IPIs which can significantly impact performance.

Approach
--------
This patch series accumulates dirty folios into batches and performs a single
TLB flush for the entire batch, rather than flushing for each individual folio.

Changes
-------
Patch 1: Refactor shrink_folio_list() to improve code readability and
maintainability by extracting common logic into helper functions:
- folio_active_bounce(): Handle folio activation logic
- folio_free(): Handle folio freeing logic
- pageout_one(): Handle single folio pageout logic

Patch 2: Implement batch TLB flushing logic. Dirty folios are accumulated
in batches and a single TLB flush is performed for each batch
before calling pageout.

Testing
-------
The benchmark script uses stress-ng to compare TLB shootdown behavior before and
after this patch. It constrains a stress-ng workload via memcg to force reclaim
through shrink_folio_list(), reporting TLB shootdowns and IPIs.

Core benchmark command: stress-ng --vm 16 --vm-bytes 2G --vm-keep --timeout 60

==========================================================================
batch_dirty_tlb_flush Benchmark Results
==========================================================================
Kernel: 7.0.0-rc1+ CPUs: 16
MemTotal: 31834M SwapTotal: 8191M
memcg limit: 512M alloc: 2G workers: 16 duration: 60s
--------------------------------------------------------------------------
Metric Before After Delta (abs / %)
--------------------------------------------------------------------------
bogo ops/s 28238.63 35833.97 +7595.34 (+26.9%)
TLB shootdowns 55428953 17621697 -37807256 (-68.2%)
Function call IPIs 34073695 14498768 -19574927 (-57.4%)
pgscan_anon (pages) 52856224 60252894 7396670 (+14.0%)
pgsteal_anon (pages) 29004962 34054753 5049791 (+17.4%)
--------------------------------------------------------------------------

Suggested-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Zhang Peng <bruzzhang@tencent.com>
---
bruzzhang (2):
mm/vmscan: refactor shrink_folio_list for readability and maintainability
mm, vmscan: flush TLB for every 31 folios evictions

include/linux/vmstat.h | 1 +
mm/vmscan.c | 387 +++++++++++++++++++++++++++++++------------------
2 files changed, 245 insertions(+), 143 deletions(-)
---
base-commit: 49cb736d092aaa856283e33b78ec3afb3964d82f
change-id: 20260309-batch-tlb-flush-893f0e56b496

Best regards,
--
Zhang Peng <zippermonkey@icloud.com>