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: Add nr_reclaimed to reclaim_stat so shrink_folio_list() can be changed
to void, giving a consistent interface where all per-pass statistics
are reported through reclaim_stat.
Patch 2: Extract the folio activation block at activate_locked into
folio_active_bounce().
Patch 3: Extract the pageout() dispatch state machine and the folio-freeing path
into pageout_one() and folio_free() respectively.
Patch 4: Extract the TTU setup and try_to_unmap() block into folio_try_unmap().
Patch 5: 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>
---
Changes in v2:
- Fix incorrect comment about page_ref_freeze
- Add folio_maybe_dma_pinned() check in pageout_batch()
- Link to v1: https://lore.kernel.org/r/20260309-batch-tlb-flush-v1-0-eb8fed7d1a9e@icloud.com
---
Zhang Peng (5):
mm/vmscan: track reclaimed pages in reclaim_stat
mm/vmscan: extract folio activation into folio_active_bounce()
mm/vmscan: extract folio_free() and pageout_one()
mm/vmscan: extract folio unmap logic into folio_try_unmap()
mm/vmscan: flush TLB for every 31 folios evictions
include/linux/vmstat.h | 1 +
mm/vmscan.c | 456 +++++++++++++++++++++++++++++++------------------
2 files changed, 287 insertions(+), 170 deletions(-)
---
base-commit: 7c5507fca017a80ece36f34e36c77e2bee267517
change-id: 20260309-batch-tlb-flush-893f0e56b496
Best regards,
--
Zhang Peng <zippermonkey@icloud.com>