[PATCH v2 0/5] mm: batch TLB flushing for dirty folios in vmscan

[PATCH v2 0/5] mm: batch TLB flushing for dirty folios in vmscan

[Zhang Peng]

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>

[PATCH v2 1/5] mm/vmscan: track reclaimed pages in reclaim_stat

[Zhang Peng]

From: Zhang Peng <bruzzhang@tencent.com>

shrink_folio_list() returns nr_reclaimed while all other statistics are
reported via reclaim_stat. Add nr_reclaimed to reclaim_stat and change
the function to void for a consistent interface.

No functional change.

Suggested-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Zhang Peng <bruzzhang@tencent.com>
---
 include/linux/vmstat.h |  1 +
 mm/vmscan.c            | 25 ++++++++++++++-----------
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 3c9c266cf782..f088c5641d99 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -26,6 +26,7 @@ struct reclaim_stat {
 	unsigned nr_unmap_fail;
 	unsigned nr_lazyfree_fail;
 	unsigned nr_demoted;
+	unsigned nr_reclaimed;
 };
 
 /* Stat data for system wide items */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5ee64cf81378..f3f03a44042e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1053,9 +1053,9 @@ static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)
 }
 
 /*
- * shrink_folio_list() returns the number of reclaimed pages
+ * Reclaimed folios are counted in stat->nr_reclaimed.
  */
-static unsigned int shrink_folio_list(struct list_head *folio_list,
+static void shrink_folio_list(struct list_head *folio_list,
 		struct pglist_data *pgdat, struct scan_control *sc,
 		struct reclaim_stat *stat, bool ignore_references,
 		struct mem_cgroup *memcg)
@@ -1063,7 +1063,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 	struct folio_batch free_folios;
 	LIST_HEAD(ret_folios);
 	LIST_HEAD(demote_folios);
-	unsigned int nr_reclaimed = 0, nr_demoted = 0;
+	unsigned int nr_demoted = 0;
 	unsigned int pgactivate = 0;
 	bool do_demote_pass;
 	struct swap_iocb *plug = NULL;
@@ -1477,7 +1477,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 					 * increment nr_reclaimed here (and
 					 * leave it off the LRU).
 					 */
-					nr_reclaimed += nr_pages;
+					stat->nr_reclaimed += nr_pages;
 					continue;
 				}
 			}
@@ -1507,7 +1507,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 		 * Folio may get swapped out as a whole, need to account
 		 * all pages in it.
 		 */
-		nr_reclaimed += nr_pages;
+		stat->nr_reclaimed += nr_pages;
 
 		folio_unqueue_deferred_split(folio);
 		if (folio_batch_add(&free_folios, folio) == 0) {
@@ -1549,7 +1549,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 
 	/* Migrate folios selected for demotion */
 	nr_demoted = demote_folio_list(&demote_folios, pgdat, memcg);
-	nr_reclaimed += nr_demoted;
+	stat->nr_reclaimed += nr_demoted;
 	stat->nr_demoted += nr_demoted;
 	/* Folios that could not be demoted are still in @demote_folios */
 	if (!list_empty(&demote_folios)) {
@@ -1589,7 +1589,6 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 
 	if (plug)
 		swap_write_unplug(plug);
-	return nr_reclaimed;
 }
 
 unsigned int reclaim_clean_pages_from_list(struct zone *zone,
@@ -1623,8 +1622,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 	 * change in the future.
 	 */
 	noreclaim_flag = memalloc_noreclaim_save();
-	nr_reclaimed = shrink_folio_list(&clean_folios, zone->zone_pgdat, &sc,
+	shrink_folio_list(&clean_folios, zone->zone_pgdat, &sc,
 					&stat, true, NULL);
+	nr_reclaimed = stat.nr_reclaimed;
 	memalloc_noreclaim_restore(noreclaim_flag);
 
 	list_splice(&clean_folios, folio_list);
@@ -1992,8 +1992,9 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 	if (nr_taken == 0)
 		return 0;
 
-	nr_reclaimed = shrink_folio_list(&folio_list, pgdat, sc, &stat, false,
+	shrink_folio_list(&folio_list, pgdat, sc, &stat, false,
 					 lruvec_memcg(lruvec));
+	nr_reclaimed = stat.nr_reclaimed;
 
 	move_folios_to_lru(&folio_list);
 
@@ -2168,7 +2169,8 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
 		.no_demotion = 1,
 	};
 
-	nr_reclaimed = shrink_folio_list(folio_list, pgdat, &sc, &stat, true, NULL);
+	shrink_folio_list(folio_list, pgdat, &sc, &stat, true, NULL);
+	nr_reclaimed = stat.nr_reclaimed;
 	while (!list_empty(folio_list)) {
 		folio = lru_to_folio(folio_list);
 		list_del(&folio->lru);
@@ -4862,7 +4864,8 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	if (list_empty(&list))
 		return scanned;
 retry:
-	reclaimed = shrink_folio_list(&list, pgdat, sc, &stat, false, memcg);
+	shrink_folio_list(&list, pgdat, sc, &stat, false, memcg);
+	reclaimed = stat.nr_reclaimed;
 	sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
 	sc->nr_reclaimed += reclaimed;
 	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,

-- 
2.43.7

[PATCH v2 0/5] mm: batch TLB flushing for dirty folios in vmscan

[Zhang Peng]

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>