* [PATCH v7 01/15] mm/mglru: consolidate common code for retrieving evictable size
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 02/15] mm/mglru: rename variables related to aging and rotation Kairui Song via B4 Relay
` (14 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Merge commonly used code for counting evictable folios in a lruvec.
No behavior change.
Acked-by: Yuanchu Xie <yuanchu@google.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 36 ++++++++++++++----------------------
1 file changed, 14 insertions(+), 22 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b2d89ed69d22..b80fbc4fc285 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4084,27 +4084,33 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
}
-static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
+static unsigned long lruvec_evictable_size(struct lruvec *lruvec, int swappiness)
{
int gen, type, zone;
- unsigned long total = 0;
- int swappiness = get_swappiness(lruvec, sc);
+ unsigned long seq, total = 0;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
- struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MAX_SEQ(lruvec);
DEFINE_MIN_SEQ(lruvec);
for_each_evictable_type(type, swappiness) {
- unsigned long seq;
-
for (seq = min_seq[type]; seq <= max_seq; seq++) {
gen = lru_gen_from_seq(seq);
-
for (zone = 0; zone < MAX_NR_ZONES; zone++)
total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
}
}
+ return total;
+}
+
+static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
+{
+ unsigned long total;
+ int swappiness = get_swappiness(lruvec, sc);
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+ total = lruvec_evictable_size(lruvec, swappiness);
+
/* whether the size is big enough to be helpful */
return mem_cgroup_online(memcg) ? (total >> sc->priority) : total;
}
@@ -4909,9 +4915,6 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
int swappiness, unsigned long *nr_to_scan)
{
- int gen, type, zone;
- unsigned long size = 0;
- struct lru_gen_folio *lrugen = &lruvec->lrugen;
DEFINE_MIN_SEQ(lruvec);
*nr_to_scan = 0;
@@ -4919,18 +4922,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
return true;
- for_each_evictable_type(type, swappiness) {
- unsigned long seq;
-
- for (seq = min_seq[type]; seq <= max_seq; seq++) {
- gen = lru_gen_from_seq(seq);
-
- for (zone = 0; zone < MAX_NR_ZONES; zone++)
- size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
- }
- }
-
- *nr_to_scan = size;
+ *nr_to_scan = lruvec_evictable_size(lruvec, swappiness);
/* better to run aging even though eviction is still possible */
return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
}
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 02/15] mm/mglru: rename variables related to aging and rotation
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 01/15] mm/mglru: consolidate common code for retrieving evictable size Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 03/15] mm/mglru: relocate the LRU scan batch limit to callers Kairui Song via B4 Relay
` (13 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
The current variable name isn't helpful. Make the variable names more
meaningful.
Only naming change, no behavior change.
Suggested-by: Barry Song <baohua@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b80fbc4fc285..7f011ff4c478 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4934,7 +4934,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
*/
static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
{
- bool success;
+ bool need_aging;
unsigned long nr_to_scan;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
DEFINE_MAX_SEQ(lruvec);
@@ -4942,7 +4942,7 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int s
if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
return -1;
- success = should_run_aging(lruvec, max_seq, swappiness, &nr_to_scan);
+ need_aging = should_run_aging(lruvec, max_seq, swappiness, &nr_to_scan);
/* try to scrape all its memory if this memcg was deleted */
if (nr_to_scan && !mem_cgroup_online(memcg))
@@ -4951,7 +4951,7 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int s
nr_to_scan = apply_proportional_protection(memcg, sc, nr_to_scan);
/* try to get away with not aging at the default priority */
- if (!success || sc->priority == DEF_PRIORITY)
+ if (!need_aging || sc->priority == DEF_PRIORITY)
return nr_to_scan >> sc->priority;
/* stop scanning this lruvec as it's low on cold folios */
@@ -5040,7 +5040,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
{
- bool success;
+ bool need_rotate;
unsigned long scanned = sc->nr_scanned;
unsigned long reclaimed = sc->nr_reclaimed;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
@@ -5058,7 +5058,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
memcg_memory_event(memcg, MEMCG_LOW);
}
- success = try_to_shrink_lruvec(lruvec, sc);
+ need_rotate = try_to_shrink_lruvec(lruvec, sc);
shrink_slab(sc->gfp_mask, pgdat->node_id, memcg, sc->priority);
@@ -5068,10 +5068,10 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
flush_reclaim_state(sc);
- if (success && mem_cgroup_online(memcg))
+ if (need_rotate && mem_cgroup_online(memcg))
return MEMCG_LRU_YOUNG;
- if (!success && lruvec_is_sizable(lruvec, sc))
+ if (!need_rotate && lruvec_is_sizable(lruvec, sc))
return 0;
/* one retry if offlined or too small */
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 03/15] mm/mglru: relocate the LRU scan batch limit to callers
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 01/15] mm/mglru: consolidate common code for retrieving evictable size Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 02/15] mm/mglru: rename variables related to aging and rotation Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 04/15] mm/mglru: restructure the reclaim loop Kairui Song via B4 Relay
` (12 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Same as active / inactive LRU, MGLRU isolates and scans folios in batches.
The batch split is done hidden deep in the helper, which makes the code
harder to follow. The helper's arguments are also confusing since callers
usually request more folios than the batch size, so the helper almost
never processes the full requested amount.
Move the batch splitting into the top loop to make it cleaner, there
should be no behavior change.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7f011ff4c478..a011733a6392 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4695,10 +4695,10 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
int scanned = 0;
int isolated = 0;
int skipped = 0;
- int scan_batch = min(nr_to_scan, MAX_LRU_BATCH);
- int remaining = scan_batch;
+ unsigned long remaining = nr_to_scan;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
+ VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
VM_WARN_ON_ONCE(!list_empty(list));
if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
@@ -4751,7 +4751,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
mod_lruvec_state(lruvec, item, isolated);
mod_lruvec_state(lruvec, PGREFILL, sorted);
mod_lruvec_state(lruvec, PGSCAN_ANON + type, isolated);
- trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, scan_batch,
+ trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
scanned, skipped, isolated,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
if (type == LRU_GEN_FILE)
@@ -4987,7 +4987,7 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
- long nr_to_scan;
+ long nr_batch, nr_to_scan;
unsigned long scanned = 0;
int swappiness = get_swappiness(lruvec, sc);
@@ -4998,7 +4998,8 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
if (nr_to_scan <= 0)
break;
- delta = evict_folios(nr_to_scan, lruvec, sc, swappiness);
+ nr_batch = min(nr_to_scan, MAX_LRU_BATCH);
+ delta = evict_folios(nr_batch, lruvec, sc, swappiness);
if (!delta)
break;
@@ -5623,6 +5624,7 @@ static int run_aging(struct lruvec *lruvec, unsigned long seq,
static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_control *sc,
int swappiness, unsigned long nr_to_reclaim)
{
+ int nr_batch;
DEFINE_MAX_SEQ(lruvec);
if (seq + MIN_NR_GENS > max_seq)
@@ -5639,8 +5641,8 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
if (sc->nr_reclaimed >= nr_to_reclaim)
return 0;
- if (!evict_folios(nr_to_reclaim - sc->nr_reclaimed, lruvec, sc,
- swappiness))
+ nr_batch = min(nr_to_reclaim - sc->nr_reclaimed, MAX_LRU_BATCH);
+ if (!evict_folios(nr_batch, lruvec, sc, swappiness))
return 0;
cond_resched();
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 04/15] mm/mglru: restructure the reclaim loop
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (2 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 03/15] mm/mglru: relocate the LRU scan batch limit to callers Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 05/15] mm/mglru: scan and count the exact number of folios Kairui Song via B4 Relay
` (11 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
The current loop will calculate the scan number on each iteration. The
number of folios to scan is based on the LRU length, with some unclear
behaviors, e.g, the scan number is only shifted by reclaim priority when
aging is not needed or when at the default priority, and it couples the
number calculation with aging and rotation.
Adjust, simplify it, and decouple aging and rotation. Just calculate the
scan number for once at the beginning of the reclaim, always respect the
reclaim priority, and make the aging and rotation more explicit.
This slightly changes how aging and offline memcg reclaim works:
Previously, aging was skipped at DEF_PRIORITY even when eviction was no
longer possible, so the reclaimer wasted an iteration until the priority
escalated. Now aging runs immediately whenever it is needed to make
progress; the DEF_PRIORITY skip only applies when eviction is still
viable. This may avoid wasted iterations that over-reclaim slab and break
reclaim balance in multi-cgroup setups.
Similar for offline memcg. Previously, offline memcg wouldn't be aged
unless it didn't have any evictable folios. Now, we might age it if it
has only 3 generations, which should be fine. On one hand, offline memcg
might still hold long-term folios, and in fact, a long-existing offline
memcg must be pinned by some long-term folios like shmem. These folios
might be used by other memcg, so aging them as ordinary memcg seems
correct. Besides, aging enables further reclaim of an offlined memcg,
which will certainly happen if we keep shrinking it. And offline memcg
might soon be no longer an issue with reparenting.
Overall, the memcg LRU rotation, as described in mmzone.h, remains the
same.
Note that because the scan budget is now pinned at loop entry, tiny
lruvec might skip this reclaim pass, also skipping aging, which could be
beneficial as aging is not helpful since it will still be un-reclaimable
after aging. Reclaim will go on as usual once priority escalates.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 72 ++++++++++++++++++++++++++++++-------------------------------
1 file changed, 36 insertions(+), 36 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a011733a6392..b247f216f28b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4913,49 +4913,37 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
}
static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
- int swappiness, unsigned long *nr_to_scan)
+ struct scan_control *sc, int swappiness)
{
DEFINE_MIN_SEQ(lruvec);
- *nr_to_scan = 0;
/* have to run aging, since eviction is not possible anymore */
if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
return true;
- *nr_to_scan = lruvec_evictable_size(lruvec, swappiness);
+ /* try to avoid aging, do gentle reclaim at the default priority */
+ if (sc->priority == DEF_PRIORITY)
+ return false;
+
/* better to run aging even though eviction is still possible */
return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
}
-/*
- * For future optimizations:
- * 1. Defer try_to_inc_max_seq() to workqueues to reduce latency for memcg
- * reclaim.
- */
-static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
+static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
+ struct mem_cgroup *memcg, int swappiness)
{
- bool need_aging;
- unsigned long nr_to_scan;
- struct mem_cgroup *memcg = lruvec_memcg(lruvec);
- DEFINE_MAX_SEQ(lruvec);
+ unsigned long nr_to_scan, evictable;
- if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
- return -1;
-
- need_aging = should_run_aging(lruvec, max_seq, swappiness, &nr_to_scan);
+ evictable = lruvec_evictable_size(lruvec, swappiness);
/* try to scrape all its memory if this memcg was deleted */
- if (nr_to_scan && !mem_cgroup_online(memcg))
- return nr_to_scan;
-
- nr_to_scan = apply_proportional_protection(memcg, sc, nr_to_scan);
+ if (!mem_cgroup_online(memcg))
+ return evictable;
- /* try to get away with not aging at the default priority */
- if (!need_aging || sc->priority == DEF_PRIORITY)
- return nr_to_scan >> sc->priority;
+ nr_to_scan = apply_proportional_protection(memcg, sc, evictable);
+ nr_to_scan >>= sc->priority;
- /* stop scanning this lruvec as it's low on cold folios */
- return try_to_inc_max_seq(lruvec, max_seq, swappiness, false) ? -1 : 0;
+ return nr_to_scan;
}
static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
@@ -4985,31 +4973,44 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
return true;
}
+/*
+ * For future optimizations:
+ * 1. Defer try_to_inc_max_seq() to workqueues to reduce latency for memcg
+ * reclaim.
+ */
static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
+ bool need_rotate = false;
long nr_batch, nr_to_scan;
- unsigned long scanned = 0;
int swappiness = get_swappiness(lruvec, sc);
+ struct mem_cgroup *memcg = lruvec_memcg(lruvec);
- while (true) {
+ nr_to_scan = get_nr_to_scan(lruvec, sc, memcg, swappiness);
+ while (nr_to_scan > 0) {
int delta;
+ DEFINE_MAX_SEQ(lruvec);
- nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness);
- if (nr_to_scan <= 0)
+ if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
+ need_rotate = true;
break;
+ }
+
+ if (should_run_aging(lruvec, max_seq, sc, swappiness)) {
+ if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
+ need_rotate = true;
+ /* stop scanning as it's low on cold folios */
+ break;
+ }
nr_batch = min(nr_to_scan, MAX_LRU_BATCH);
delta = evict_folios(nr_batch, lruvec, sc, swappiness);
if (!delta)
break;
- scanned += delta;
- if (scanned >= nr_to_scan)
- break;
-
if (should_abort_scan(lruvec, sc))
break;
+ nr_to_scan -= delta;
cond_resched();
}
@@ -5035,8 +5036,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
}
- /* whether this lruvec should be rotated */
- return nr_to_scan < 0;
+ return need_rotate;
}
static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 05/15] mm/mglru: scan and count the exact number of folios
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (3 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 04/15] mm/mglru: restructure the reclaim loop Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 06/15] mm/mglru: avoid reclaim type fall back when isolation makes no progress Kairui Song via B4 Relay
` (10 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Make the scan helpers return the exact number of folios being scanned or
isolated. Since the reclaim loop now has a natural scan budget that
controls the scan progress, returning the scan number and consuming the
budget makes the scan more accurate and easier to follow.
The number of scanned folios for each iteration is always larger than 0,
unless the reclaim must stop for a forced aging, so there is no more need
for any special handling when there is no progress made:
- `return isolated || !remaining ? scanned : 0` in scan_folios: both
the function and the call now just return the exact scan count,
combined with the scan budget introduced in the previous commit to
avoid livelock or under scan.
- `scanned += try_to_inc_min_seq` in evict_folios: adding a bool as
a scan count was kind of confusing and no longer needed, as scan
number should never be zero as long as there are still evictable
gens. We may encounter a empty old gen that returns 0 scan count,
to avoid that, do a try_to_inc_min_seq before toisolation which
have slight to none overhead in most cases.
- `evictable_min_seq + MIN_NR_GENS > max_seq` guard in evict_folios:
the per-type get_nr_gens == MIN_NR_GENS check in scan_folios
naturally returns 0 when only two gens remain and breaks the loop.
Also change try_to_inc_min_seq to return void, as its return value is no
longer used by any caller. Call it before isolate_folios to flush any
empty gens left by external folio freeing, and again after isolate_folios
when scanning moved or protected folios may have emptied the oldest gen.
The scan still stops if only two gens are left, as the scan number will be
zero. This matches the previous behavior. This forced gen protection may
be removed or softened later to improve reclaim further.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 58 +++++++++++++++++++++++++++++-----------------------------
1 file changed, 29 insertions(+), 29 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b247f216f28b..2dbd39e29dfc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3878,10 +3878,9 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
return true;
}
-static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
+static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
{
int gen, type, zone;
- bool success = false;
bool seq_inc_flag = false;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
DEFINE_MIN_SEQ(lruvec);
@@ -3907,11 +3906,10 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
/*
* If min_seq[type] of both anonymous and file is not increased,
- * we can directly return false to avoid unnecessary checking
- * overhead later.
+ * return here to avoid unnecessary checking overhead later.
*/
if (!seq_inc_flag)
- return success;
+ return;
/* see the comment on lru_gen_folio */
if (swappiness && swappiness <= MAX_SWAPPINESS) {
@@ -3929,10 +3927,7 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
reset_ctrl_pos(lruvec, type, true);
WRITE_ONCE(lrugen->min_seq[type], min_seq[type]);
- success = true;
}
-
- return success;
}
static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness)
@@ -4686,7 +4681,7 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
struct scan_control *sc, int type, int tier,
- struct list_head *list)
+ struct list_head *list, int *isolatedp)
{
int i;
int gen;
@@ -4756,11 +4751,9 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
if (type == LRU_GEN_FILE)
sc->nr.file_taken += isolated;
- /*
- * There might not be eligible folios due to reclaim_idx. Check the
- * remaining to prevent livelock if it's not making progress.
- */
- return isolated || !remaining ? scanned : 0;
+
+ *isolatedp = isolated;
+ return scanned;
}
static int get_tier_idx(struct lruvec *lruvec, int type)
@@ -4804,33 +4797,36 @@ static int get_type_to_scan(struct lruvec *lruvec, int swappiness)
static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
struct scan_control *sc, int swappiness,
- int *type_scanned, struct list_head *list)
+ struct list_head *list, int *isolated,
+ int *isolate_type, int *isolate_scanned)
{
int i;
+ int total_scanned = 0;
int type = get_type_to_scan(lruvec, swappiness);
for_each_evictable_type(i, swappiness) {
int scanned;
int tier = get_tier_idx(lruvec, type);
- *type_scanned = type;
+ scanned = scan_folios(nr_to_scan, lruvec, sc,
+ type, tier, list, isolated);
- scanned = scan_folios(nr_to_scan, lruvec, sc, type, tier, list);
- if (scanned)
- return scanned;
+ total_scanned += scanned;
+ if (*isolated) {
+ *isolate_type = type;
+ *isolate_scanned = scanned;
+ break;
+ }
type = !type;
}
- return 0;
+ return total_scanned;
}
static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
struct scan_control *sc, int swappiness)
{
- int type;
- int scanned;
- int reclaimed;
LIST_HEAD(list);
LIST_HEAD(clean);
struct folio *folio;
@@ -4838,19 +4834,23 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
enum node_stat_item item;
struct reclaim_stat stat;
struct lru_gen_mm_walk *walk;
+ int scanned, reclaimed;
+ int isolated = 0, type, type_scanned;
bool skip_retry = false;
- struct lru_gen_folio *lrugen = &lruvec->lrugen;
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
lruvec_lock_irq(lruvec);
- scanned = isolate_folios(nr_to_scan, lruvec, sc, swappiness, &type, &list);
+ /* In case folio deletion left empty old gens, flush them */
+ try_to_inc_min_seq(lruvec, swappiness);
- scanned += try_to_inc_min_seq(lruvec, swappiness);
+ scanned = isolate_folios(nr_to_scan, lruvec, sc, swappiness,
+ &list, &isolated, &type, &type_scanned);
- if (evictable_min_seq(lrugen->min_seq, swappiness) + MIN_NR_GENS > lrugen->max_seq)
- scanned = 0;
+ /* Scanning may have emptied the oldest gen, flush it */
+ if (scanned)
+ try_to_inc_min_seq(lruvec, swappiness);
lruvec_unlock_irq(lruvec);
@@ -4861,7 +4861,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
sc->nr_reclaimed += reclaimed;
trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
- scanned, reclaimed, &stat, sc->priority,
+ type_scanned, reclaimed, &stat, sc->priority,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
list_for_each_entry_safe_reverse(folio, next, &list, lru) {
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 06/15] mm/mglru: avoid reclaim type fall back when isolation makes no progress
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (4 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 05/15] mm/mglru: scan and count the exact number of folios Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-28 4:18 ` Kairui Song
2026-04-27 18:06 ` [PATCH v7 07/15] mm/mglru: use a smaller batch for reclaim Kairui Song via B4 Relay
` (9 subsequent siblings)
15 siblings, 1 reply; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: "Barry Song (Xiaomi)" <baohua@kernel.org>
While isolation makes no progress in scan_folios(), we quickly fall back
to the other type in isolate_folios(). This is incorrect, as the current
type may still have sufficient folios. Falling back can undermine the
positive_ctrl_err() result from get_type_to_scan(), which is derived
from swappiness.
So just continue scanning this type for another round.
Worth noting if the cold generations are all reclaimed, scan will no
longer make any progress either, which may undermine the swappiness
again. This is not a new issue and hence better be fixed later [1].
Link: https://lore.kernel.org/linux-mm/CAGsJ_4zjdOYEtuO6gNjABm7NDxW0skzBFNRNee-k2D6VwsYEQA@mail.gmail.com/ [1]
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Reviewed-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2dbd39e29dfc..ac9d2d4f8e65 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4817,8 +4817,13 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
*isolate_scanned = scanned;
break;
}
-
- type = !type;
+ /*
+ * If scanned > 0 and isolated == 0, avoid falling back to the
+ * other type, as this type remains sufficient. Falling back
+ * too readily can disrupt the positive_ctrl_err() bias.
+ */
+ if (!scanned)
+ type = !type;
}
return total_scanned;
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* Re: [PATCH v7 06/15] mm/mglru: avoid reclaim type fall back when isolation makes no progress
2026-04-27 18:06 ` [PATCH v7 06/15] mm/mglru: avoid reclaim type fall back when isolation makes no progress Kairui Song via B4 Relay
@ 2026-04-28 4:18 ` Kairui Song
0 siblings, 0 replies; 18+ messages in thread
From: Kairui Song @ 2026-04-28 4:18 UTC (permalink / raw)
To: kasong
Cc: linux-mm, Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel, Qi Zheng
Forwarding sashiko review, which I think is just false positives, just
to make things clear:
> commit dd4c6bd11860d1bc69ef77e9f0d457abec425fc6
> Author: Barry Song (Xiaomi) <baohua@kernel.org>
> mm/mglru: avoid reclaim type fall back when isolation makes no progress
> This commit modifies isolate_folios() to only fallback to the alternate LRU
> type if no folios were scanned. This prevents falling back when folios are
> scanned but none are isolated.
> Link: https://lore.kernel.org/linux-mm/CAGsJ_4zjdOYEtuO6gNjABm7NDxW0skzBFNRNee-k2D6VwsYEQA@mail.gmail.com/ [1]
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 43c0f22f15d5..304d5a4704ec 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4817,8 +4817,13 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
> > *isolate_scanned = scanned;
> > break;
> > }
> > -
> > - type = !type;
> > + /*
> > + * If scanned > 0 and isolated == 0, avoid falling back to the
> > + * other type, as this type remains sufficient. Falling back
> > + * too readily can disrupt the positive_ctrl_err() bias.
> > + */
> > + if (!scanned)
> > + type = !type;
> > }
> >
> > return total_scanned;
> Could skipping this fallback cause a livelock when folios are evictable but
> un-isolatable?
No. The total scan budget in try_to_shrink_lruvec() bounds the loop and scanned
folios are moved to newer gen. And we used to skip it here just fine, this
commit just restored that behavior.
> For example, in constrained direct reclaim like GFP_NOIO, isolate_folio()
> can early-reject anonymous folios due to missing __GFP_IO and return false.
> When scan_folios() places these rejected folios into a temporary list and
> splices them back at the head of the oldest generation's list, this code
> path will see scanned > 0 but isolated == 0.
> Because the fallback is skipped, isolate_folios() scans the exact same LRU
> type on the next iteration. It encounters the identical un-isolatable
> folios at the head of the list, skips them again, and returns 0 isolated
> folios.
> When try_to_shrink_lruvec() decrements nr_to_scan and retries, no memory
> has been reclaimed, so the MGLRU statistics are unchanged.
> get_type_to_scan() will then select the exact same blocked LRU type again.
> Will this starve the alternate LRU type and potentially trigger premature
> OOMs?
No. Folios stuck in a non-reclaimable state (GFP_NOIO anon, writeback-waiting
file, etc.) is a pre-existing concern orthogonal to this change, and it also
applies to the fallback type
Falling back to another type is still done if we ran out of gens (scan
consumes cold gen). In following commit the writeback throttling we just
introduced improves the folio stuck in non-reclaimable state issue but
not related to this commit.
> I note this behavior is addressed later in the patch series by commit
> 8992ac501e543b77bf0d5e24175632b6eba8086c, which removes the redundant swap
> constraint check. That allows the folios to be isolated and promoted, emptying
> the oldest generation so scanned can become 0. However, does this patch
> introduce an intermediate bisection regression for the LRU fallback mechanism?
No, as said above, that's not related.
^ permalink raw reply [flat|nested] 18+ messages in thread
* [PATCH v7 07/15] mm/mglru: use a smaller batch for reclaim
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (5 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 06/15] mm/mglru: avoid reclaim type fall back when isolation makes no progress Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:06 ` [PATCH v7 08/15] mm/mglru: don't abort scan immediately right after aging Kairui Song via B4 Relay
` (8 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
With a fixed number to reclaim calculated at the beginning, making each
following step smaller should reduce the lock contention and avoid
over-aggressive reclaim of folios, as it will abort earlier when the
number of folios to be reclaimed is reached.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ac9d2d4f8e65..2a607546277c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5007,7 +5007,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
break;
}
- nr_batch = min(nr_to_scan, MAX_LRU_BATCH);
+ nr_batch = min(nr_to_scan, MIN_LRU_BATCH);
delta = evict_folios(nr_batch, lruvec, sc, swappiness);
if (!delta)
break;
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 08/15] mm/mglru: don't abort scan immediately right after aging
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (6 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 07/15] mm/mglru: use a smaller batch for reclaim Kairui Song via B4 Relay
@ 2026-04-27 18:06 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 09/15] mm/mglru: remove redundant swap constrained check upon isolation Kairui Song via B4 Relay
` (7 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:06 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Right now, if eviction triggers aging, the reclaimer will abort. This is
not the optimal strategy for several reasons.
Aborting the reclaim early wastes a reclaim cycle when under pressure, and
for concurrent reclaim, if the LRU is under aging, all concurrent
reclaimers might fail. And if the age has just finished, new cold folios
exposed by the aging are not reclaimed until the next reclaim iteration.
What's more, the current aging trigger is quite lenient, having 3 gens
with a reclaim priority lower than default will trigger aging, and blocks
reclaiming from one memcg. This wastes reclaim retry cycles easily. And
in the worst case, if the reclaim is making slower progress and all
following attempts fail due to being blocked by aging, it triggers
unexpected early OOM.
And if a lruvec requires aging, it doesn't mean it's hot. Instead, the
lruvec could be idle for quite a while, and hence it might contain lots of
cold folios to be reclaimed.
While it's helpful to rotate memcg LRU after aging for global reclaim, as
global reclaim fairness is coupled with the rotation in shrink_many, memcg
fairness is instead handled by cgroup iteration in shrink_node_memcgs.
So, for memcg level pressure, this abort is not the key part for keeping
the fairness. And in most cases, there is no need to age, and fairness
must be achieved by upper-level reclaim control.
So instead, just keep the scanning going unless one whole batch of folios
failed to be isolated or enough folios have been scanned, which is
triggered by evict_folios returning 0. And only abort for global reclaim
after one batch, so when there are fewer memcgs, progress is still made,
and the fairness mechanism described above still works fine.
And in most cases, the one more batch attempt for global reclaim might
just be enough to satisfy what the reclaimer needs, hence improving global
reclaim performance by reducing reclaim retry cycles.
Rotation is still there after the reclaim is done, which still follows the
comment in mmzone.h. And fairness still looking good.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2a607546277c..42ccc6eb0748 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4985,7 +4985,7 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
*/
static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
- bool need_rotate = false;
+ bool need_rotate = false, should_age = false;
long nr_batch, nr_to_scan;
int swappiness = get_swappiness(lruvec, sc);
struct mem_cgroup *memcg = lruvec_memcg(lruvec);
@@ -5003,8 +5003,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
if (should_run_aging(lruvec, max_seq, sc, swappiness)) {
if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
need_rotate = true;
- /* stop scanning as it's low on cold folios */
- break;
+ should_age = true;
}
nr_batch = min(nr_to_scan, MIN_LRU_BATCH);
@@ -5015,6 +5014,13 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
if (should_abort_scan(lruvec, sc))
break;
+ /*
+ * Root reclaim needs rotation when low on cold folio for better
+ * fairness. Cgroup reclaim gets fairness from the iterator.
+ */
+ if (root_reclaim(sc) && should_age)
+ break;
+
nr_to_scan -= delta;
cond_resched();
}
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 09/15] mm/mglru: remove redundant swap constrained check upon isolation
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (7 preceding siblings ...)
2026-04-27 18:06 ` [PATCH v7 08/15] mm/mglru: don't abort scan immediately right after aging Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 10/15] mm/mglru: use the common routine for dirty/writeback reactivation Kairui Song via B4 Relay
` (6 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Remove the swap-constrained early reject check upon isolation. This check
is a micro optimization when swap IO is not allowed, so folios are
rejected early. But it is redundant and overly broad since
shrink_folio_list() already handles all these cases with proper
granularity.
Notably, this check wrongly rejected lazyfree folios, and it doesn't cover
all rejection cases. shrink_folio_list() uses may_enter_fs(), which
distinguishes non-SWP_FS_OPS devices from filesystem-backed swap and does
all the checks after folio is locked, so flags like swap cache are stable.
This check also covers dirty file folios, which are not a problem now
since sort_folio() already bumps dirty file folios to the next generation,
but causes trouble for unifying dirty folio writeback handling.
And there should be no performance impact from removing it. We may have
lost a micro optimization, but unblocked lazyfree reclaim for NOIO
contexts, which is not a common case in the first place.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 42ccc6eb0748..ea86297b604c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4650,12 +4650,6 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
{
bool success;
- /* swap constrained */
- if (!(sc->gfp_mask & __GFP_IO) &&
- (folio_test_dirty(folio) ||
- (folio_test_anon(folio) && !folio_test_swapcache(folio))))
- return false;
-
/* raced with release_pages() */
if (!folio_try_get(folio))
return false;
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 10/15] mm/mglru: use the common routine for dirty/writeback reactivation
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (8 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 09/15] mm/mglru: remove redundant swap constrained check upon isolation Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 11/15] mm/mglru: simplify and improve dirty writeback handling Kairui Song via B4 Relay
` (5 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Currently MGLRU will move the dirty writeback folios to the second oldest
gen instead of reactivate them like the classical LRU. This might help to
reduce the LRU contention as it skipped the isolation. But as a result we
will see these folios at the LRU tail more frequently leading to
inefficient reclaim.
Besides, the dirty / writeback check after isolation in shrink_folio_list
is more accurate and covers more cases. So instead, just drop the special
handling for dirty writeback, use the common routine and re-activate it
like the classical LRU.
This should in theory improve the scan efficiency. These folios will be
rotated back to LRU tail once writeback is done so there is no risk of
hotness inversion. And now each reclaim loop will have a higher success
rate. This also prepares for unifying the writeback and throttling
mechanism with classical LRU, we keep these folios far from tail so
detecting the tail batch will have a similar pattern with classical LRU.
The micro optimization that avoids LRU contention by skipping the
isolation is gone, which should be fine. Compared to IO and writeback
cost, the isolation overhead is trivial.
And using the common routine also keeps the folio's referenced bits (tier
bits), which could improve metrics in the long term. Also no more need to
clean reclaim bit as the common routine will make use of it.
Note the common routine updates a few throttling and writeback counters,
which are not used, and never have been for the MGLRU case. We will start
making use of these in later commits.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 19 -------------------
1 file changed, 19 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ea86297b604c..bb7e2cecf48e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4578,7 +4578,6 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
int tier_idx)
{
bool success;
- bool dirty, writeback;
int gen = folio_lru_gen(folio);
int type = folio_is_file_lru(folio);
int zone = folio_zonenum(folio);
@@ -4628,21 +4627,6 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
return true;
}
- dirty = folio_test_dirty(folio);
- writeback = folio_test_writeback(folio);
- if (type == LRU_GEN_FILE && dirty) {
- sc->nr.file_taken += delta;
- if (!writeback)
- sc->nr.unqueued_dirty += delta;
- }
-
- /* waiting for writeback */
- if (writeback || (type == LRU_GEN_FILE && dirty)) {
- gen = folio_inc_gen(lruvec, folio, true);
- list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
- return true;
- }
-
return false;
}
@@ -4664,9 +4648,6 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
if (!folio_test_referenced(folio))
set_mask_bits(&folio->flags.f, LRU_REFS_MASK, 0);
- /* for shrink_folio_list() */
- folio_clear_reclaim(folio);
-
success = lru_gen_del_folio(lruvec, folio, true);
VM_WARN_ON_ONCE_FOLIO(!success, folio);
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 11/15] mm/mglru: simplify and improve dirty writeback handling
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (9 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 10/15] mm/mglru: use the common routine for dirty/writeback reactivation Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 12/15] mm/mglru: remove no longer used reclaim argument for folio protection Kairui Song via B4 Relay
` (4 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Right now the flusher wakeup mechanism for MGLRU is less responsive and
unlikely to trigger compared to classical LRU. The classical LRU wakes
the flusher if one batch of folios passed to shrink_folio_list is
unevictable due to under writeback. MGLRU instead check and handle this
after the whole reclaim loop is done.
We previously even saw OOM problems due to passive flusher, which were
fixed but still not perfect [1].
We have just unified the dirty folio counting and activation routine, now
just move the dirty flush into the loop right after shrink_folio_list.
This improves the performance a lot for workloads involving heavy
writeback and prepares for throttling too.
Test with YCSB workloadb showed a major performance improvement:
Before this series:
Throughput(ops/sec): 62485.02962831822
AverageLatency(us): 500.9746963330107
pgpgin 159347462
workingset_refault_file 34522071
After this commit:
Throughput(ops/sec): 80857.08510208207
AverageLatency(us): 386.653262968934
pgpgin 112233121
workingset_refault_file 19516246
The performance is a lot better with significantly lower refault. We also
observed similar or higher performance gain for other real-world
workloads.
We were concerned that the dirty flush could cause more wear for SSD: that
should not be the problem here, since the wakeup condition is when the
dirty folios have been pushed to the tail of LRU, which indicates that
memory pressure is so high that writeback is blocking the workload
already.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Link: https://lore.kernel.org/linux-mm/20241026115714.1437435-1-jingxiangzeng.cas@gmail.com/ [1]
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 41 ++++++++++++++++-------------------------
1 file changed, 16 insertions(+), 25 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bb7e2cecf48e..244cdae99573 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4724,8 +4724,6 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
scanned, skipped, isolated,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
- if (type == LRU_GEN_FILE)
- sc->nr.file_taken += isolated;
*isolatedp = isolated;
return scanned;
@@ -4838,12 +4836,27 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
return scanned;
retry:
reclaimed = shrink_folio_list(&list, pgdat, sc, &stat, false, memcg);
- sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
sc->nr_reclaimed += reclaimed;
trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
type_scanned, reclaimed, &stat, sc->priority,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
+ /*
+ * If too many file cache in the coldest generation can't be evicted
+ * due to being dirty, wake up the flusher.
+ */
+ if (stat.nr_unqueued_dirty == isolated) {
+ wakeup_flusher_threads(WB_REASON_VMSCAN);
+
+ /*
+ * For cgroupv1 dirty throttling is achieved by waking up
+ * the kernel flusher here and later waiting on folios
+ * which are in writeback to finish (see shrink_folio_list()).
+ */
+ if (!writeback_throttling_sane(sc))
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+ }
+
list_for_each_entry_safe_reverse(folio, next, &list, lru) {
DEFINE_MIN_SEQ(lruvec);
@@ -5000,28 +5013,6 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
cond_resched();
}
- /*
- * If too many file cache in the coldest generation can't be evicted
- * due to being dirty, wake up the flusher.
- */
- if (sc->nr.unqueued_dirty && sc->nr.unqueued_dirty == sc->nr.file_taken) {
- struct pglist_data *pgdat = lruvec_pgdat(lruvec);
-
- wakeup_flusher_threads(WB_REASON_VMSCAN);
-
- /*
- * For cgroupv1 dirty throttling is achieved by waking up
- * the kernel flusher here and later waiting on folios
- * which are in writeback to finish (see shrink_folio_list()).
- *
- * Flusher may not be able to issue writeback quickly
- * enough for cgroupv1 writeback throttling to work
- * on a large system.
- */
- if (!writeback_throttling_sane(sc))
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
- }
-
return need_rotate;
}
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 12/15] mm/mglru: remove no longer used reclaim argument for folio protection
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (10 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 11/15] mm/mglru: simplify and improve dirty writeback handling Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 13/15] mm/vmscan: remove sc->file_taken Kairui Song via B4 Relay
` (3 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Now dirty reclaim folios are handled after isolation, not before, since
dirty reactivation must take the folio off LRU first, and that helps to
unify the dirty handling logic.
So this argument is no longer needed. Just remove it.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 244cdae99573..eb7eb2ed1830 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3220,7 +3220,7 @@ static int folio_update_gen(struct folio *folio, int gen)
}
/* protect pages accessed multiple times through file descriptors */
-static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
+static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio)
{
int type = folio_is_file_lru(folio);
struct lru_gen_folio *lrugen = &lruvec->lrugen;
@@ -3239,9 +3239,6 @@ static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclai
new_flags = old_flags & ~(LRU_GEN_MASK | LRU_REFS_FLAGS);
new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
- /* for folio_end_writeback() */
- if (reclaiming)
- new_flags |= BIT(PG_reclaim);
} while (!try_cmpxchg(&folio->flags.f, &old_flags, new_flags));
lru_gen_update_size(lruvec, folio, old_gen, new_gen);
@@ -3855,7 +3852,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
- new_gen = folio_inc_gen(lruvec, folio, false);
+ new_gen = folio_inc_gen(lruvec, folio);
list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
/* don't count the workingset being lazily promoted */
@@ -4607,7 +4604,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
/* protected */
if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) {
- gen = folio_inc_gen(lruvec, folio, false);
+ gen = folio_inc_gen(lruvec, folio);
list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
/* don't count the workingset being lazily promoted */
@@ -4622,7 +4619,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
/* ineligible */
if (zone > sc->reclaim_idx) {
- gen = folio_inc_gen(lruvec, folio, false);
+ gen = folio_inc_gen(lruvec, folio);
list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
return true;
}
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 13/15] mm/vmscan: remove sc->file_taken
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (11 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 12/15] mm/mglru: remove no longer used reclaim argument for folio protection Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 14/15] mm/vmscan: remove sc->unqueued_dirty Kairui Song via B4 Relay
` (2 subsequent siblings)
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
No one is using it now, just remove it.
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb7eb2ed1830..a071f7444232 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -173,7 +173,6 @@ struct scan_control {
unsigned int congested;
unsigned int writeback;
unsigned int immediate;
- unsigned int file_taken;
unsigned int taken;
} nr;
@@ -2040,8 +2039,6 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
sc->nr.writeback += stat.nr_writeback;
sc->nr.immediate += stat.nr_immediate;
sc->nr.taken += nr_taken;
- if (file)
- sc->nr.file_taken += nr_taken;
trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
nr_scanned, nr_reclaimed, &stat, sc->priority, file);
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 14/15] mm/vmscan: remove sc->unqueued_dirty
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (12 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 13/15] mm/vmscan: remove sc->file_taken Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:07 ` [PATCH v7 15/15] mm/vmscan: unify writeback reclaim statistic and throttling Kairui Song via B4 Relay
2026-04-27 18:22 ` [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Andrew Morton
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
No one is using it now, just remove it.
Suggested-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a071f7444232..902ca52ca381 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -169,7 +169,6 @@ struct scan_control {
struct {
unsigned int dirty;
- unsigned int unqueued_dirty;
unsigned int congested;
unsigned int writeback;
unsigned int immediate;
@@ -2035,7 +2034,6 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
sc->nr.dirty += stat.nr_dirty;
sc->nr.congested += stat.nr_congested;
- sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
sc->nr.writeback += stat.nr_writeback;
sc->nr.immediate += stat.nr_immediate;
sc->nr.taken += nr_taken;
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* [PATCH v7 15/15] mm/vmscan: unify writeback reclaim statistic and throttling
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (13 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 14/15] mm/vmscan: remove sc->unqueued_dirty Kairui Song via B4 Relay
@ 2026-04-27 18:07 ` Kairui Song via B4 Relay
2026-04-27 18:22 ` [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Andrew Morton
15 siblings, 0 replies; 18+ messages in thread
From: Kairui Song via B4 Relay @ 2026-04-27 18:07 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, Axel Rasmussen, Yuanchu Xie, Wei Xu, Kairui Song,
Johannes Weiner, David Hildenbrand, Michal Hocko, Shakeel Butt,
Lorenzo Stoakes, Barry Song, David Stevens, Chen Ridong, Leno Hou,
Yafang Shao, Yu Zhao, Zicheng Wang, Baolin Wang, Kalesh Singh,
Suren Baghdasaryan, Chris Li, Vernon Yang, linux-kernel,
linux-kernel, Kairui Song, Qi Zheng
From: Kairui Song <kasong@tencent.com>
Currently MGLRU and non-MGLRU handle the reclaim statistic and writeback
handling very differently, especially throttling. Basically MGLRU just
ignored the throttling part.
Let's just unify this part, use a helper to deduplicate the code so both
setups will share the same behavior.
Test using following reproducer using bash:
echo "Setup a slow device using dm delay"
dd if=/dev/zero of=/var/tmp/backing bs=1M count=2048
LOOP=$(losetup --show -f /var/tmp/backing)
mkfs.ext4 -q $LOOP
echo "0 $(blockdev --getsz $LOOP) delay $LOOP 0 0 $LOOP 0 1000" | \
dmsetup create slow_dev
mkdir -p /mnt/slow && mount /dev/mapper/slow_dev /mnt/slow
echo "Start writeback pressure"
sync && echo 3 > /proc/sys/vm/drop_caches
mkdir /sys/fs/cgroup/test_wb
echo 128M > /sys/fs/cgroup/test_wb/memory.max
(echo $BASHPID > /sys/fs/cgroup/test_wb/cgroup.procs && \
dd if=/dev/zero of=/mnt/slow/testfile bs=1M count=192)
echo "Clean up"
echo "0 $(blockdev --getsz $LOOP) error" | dmsetup load slow_dev
dmsetup resume slow_dev
umount -l /mnt/slow && sync
dmsetup remove slow_dev
Before this commit, `dd` will get OOM killed immediately if MGLRU is
enabled. Classic LRU is fine.
After this commit, throttling is now effective and no more spin on LRU or
premature OOM. Stress test on other workloads also looks good.
Global throttling is not here yet, we will fix that separately later.
Suggested-by: Chen Ridong <chenridong@huaweicloud.com>
Tested-by: Leno Hou <lenohou@gmail.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/vmscan.c | 92 +++++++++++++++++++++++++++++--------------------------------
1 file changed, 43 insertions(+), 49 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 902ca52ca381..e452cb043d46 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1942,6 +1942,44 @@ static int current_may_throttle(void)
return !(current->flags & PF_LOCAL_THROTTLE);
}
+static void handle_reclaim_writeback(unsigned long nr_taken,
+ struct pglist_data *pgdat,
+ struct scan_control *sc,
+ struct reclaim_stat *stat)
+{
+ /*
+ * If dirty folios are scanned that are not queued for IO, it
+ * implies that flushers are not doing their job. This can
+ * happen when memory pressure pushes dirty folios to the end of
+ * the LRU before the dirty limits are breached and the dirty
+ * data has expired. It can also happen when the proportion of
+ * dirty folios grows not through writes but through memory
+ * pressure reclaiming all the clean cache. And in some cases,
+ * the flushers simply cannot keep up with the allocation
+ * rate. Nudge the flusher threads in case they are asleep.
+ */
+ if (stat->nr_unqueued_dirty == nr_taken) {
+ wakeup_flusher_threads(WB_REASON_VMSCAN);
+ /*
+ * For cgroupv1 dirty throttling is achieved by waking up
+ * the kernel flusher here and later waiting on folios
+ * which are in writeback to finish (see shrink_folio_list()).
+ *
+ * Flusher may not be able to issue writeback quickly
+ * enough for cgroupv1 writeback throttling to work
+ * on a large system.
+ */
+ if (!writeback_throttling_sane(sc))
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+ }
+
+ sc->nr.dirty += stat->nr_dirty;
+ sc->nr.congested += stat->nr_congested;
+ sc->nr.writeback += stat->nr_writeback;
+ sc->nr.immediate += stat->nr_immediate;
+ sc->nr.taken += nr_taken;
+}
+
/*
* shrink_inactive_list() is a helper for shrink_node(). It returns the number
* of reclaimed pages
@@ -2005,39 +2043,7 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
lruvec_lock_irq(lruvec);
lru_note_cost_unlock_irq(lruvec, file, stat.nr_pageout,
nr_scanned - nr_reclaimed);
-
- /*
- * If dirty folios are scanned that are not queued for IO, it
- * implies that flushers are not doing their job. This can
- * happen when memory pressure pushes dirty folios to the end of
- * the LRU before the dirty limits are breached and the dirty
- * data has expired. It can also happen when the proportion of
- * dirty folios grows not through writes but through memory
- * pressure reclaiming all the clean cache. And in some cases,
- * the flushers simply cannot keep up with the allocation
- * rate. Nudge the flusher threads in case they are asleep.
- */
- if (stat.nr_unqueued_dirty == nr_taken) {
- wakeup_flusher_threads(WB_REASON_VMSCAN);
- /*
- * For cgroupv1 dirty throttling is achieved by waking up
- * the kernel flusher here and later waiting on folios
- * which are in writeback to finish (see shrink_folio_list()).
- *
- * Flusher may not be able to issue writeback quickly
- * enough for cgroupv1 writeback throttling to work
- * on a large system.
- */
- if (!writeback_throttling_sane(sc))
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
- }
-
- sc->nr.dirty += stat.nr_dirty;
- sc->nr.congested += stat.nr_congested;
- sc->nr.writeback += stat.nr_writeback;
- sc->nr.immediate += stat.nr_immediate;
- sc->nr.taken += nr_taken;
-
+ handle_reclaim_writeback(nr_taken, pgdat, sc, &stat);
trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
nr_scanned, nr_reclaimed, &stat, sc->priority, file);
return nr_reclaimed;
@@ -4829,26 +4835,13 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
retry:
reclaimed = shrink_folio_list(&list, pgdat, sc, &stat, false, memcg);
sc->nr_reclaimed += reclaimed;
+ /* Retry pass is only meant for clean folios without new isolation */
+ if (isolated)
+ handle_reclaim_writeback(isolated, pgdat, sc, &stat);
trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
type_scanned, reclaimed, &stat, sc->priority,
type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
- /*
- * If too many file cache in the coldest generation can't be evicted
- * due to being dirty, wake up the flusher.
- */
- if (stat.nr_unqueued_dirty == isolated) {
- wakeup_flusher_threads(WB_REASON_VMSCAN);
-
- /*
- * For cgroupv1 dirty throttling is achieved by waking up
- * the kernel flusher here and later waiting on folios
- * which are in writeback to finish (see shrink_folio_list()).
- */
- if (!writeback_throttling_sane(sc))
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
- }
-
list_for_each_entry_safe_reverse(folio, next, &list, lru) {
DEFINE_MIN_SEQ(lruvec);
@@ -4891,6 +4884,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
if (!list_empty(&list)) {
skip_retry = true;
+ isolated = 0;
goto retry;
}
--
2.54.0
^ permalink raw reply related [flat|nested] 18+ messages in thread* Re: [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling
2026-04-27 18:06 [PATCH v7 00/15] mm/mglru: improve reclaim loop and dirty folio handling Kairui Song via B4 Relay
` (14 preceding siblings ...)
2026-04-27 18:07 ` [PATCH v7 15/15] mm/vmscan: unify writeback reclaim statistic and throttling Kairui Song via B4 Relay
@ 2026-04-27 18:22 ` Andrew Morton
15 siblings, 0 replies; 18+ messages in thread
From: Andrew Morton @ 2026-04-27 18:22 UTC (permalink / raw)
To: kasong
Cc: Kairui Song via B4 Relay, linux-mm, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Johannes Weiner, David Hildenbrand, Michal Hocko,
Shakeel Butt, Lorenzo Stoakes, Barry Song, David Stevens,
Chen Ridong, Leno Hou, Yafang Shao, Yu Zhao, Zicheng Wang,
Baolin Wang, Kalesh Singh, Suren Baghdasaryan, Chris Li,
Vernon Yang, linux-kernel, Kairui Song, Qi Zheng
On Tue, 28 Apr 2026 02:06:51 +0800 Kairui Song via B4 Relay <devnull+kasong.tencent.com@kernel.org> wrote:
> From: Kairui Song <kasong@tencent.com>
>
> This series cleans up and slightly improves MGLRU's reclaim loop and
> dirty writeback handling. As a result, we can see an up to ~30% increase
> in some workloads like MongoDB with YCSB and a huge decrease in file
> refault, no swap involved. Other common benchmarks have no regression,
> and LOC is reduced, with less unexpected OOM, too.
Thanks, I've updated mm.git's mm-new branch to this version.
> Changes in v7:
> - Fix swappiness not being effective with a standalone fix patch
> from Barry Song. It's OK to be a standalone fix since that is not a
> major bug but an unexpected behavior change, and shouldn't effect any
> bisecting. I slightly adjusted the commit message as the subjcect is too
> long and getting truncated for mail:
> https://lore.kernel.org/linux-mm/20260425205759.1701-1-baohua@kernel.org/
> - Remove the min limit for calculating nr_to_scan:
> https://lore.kernel.org/linux-mm/aet1hd9DfRH4aSOO@KASONG-MC4/
> Instead just revert to V1:
> https://sashiko.dev/#/message/20260318-mglru-reclaim-v1-3-2c46f9eb0508%40tencent.com
> Everyone was fine with that, the min limit in later version was
> introduced to cover sashiko's review on V1, but now think again, that's
> actually not a bug and instead could be beneficial. This min
> check doesn't always make sense and there isn't any practical issue observed.
> - Retest still looking very good in every case.
Here's how v7 altered mm.git. (Looks small - did I mess this up?)
--- a/mm/vmscan.c~b
+++ a/mm/vmscan.c
@@ -4788,8 +4788,13 @@ static int isolate_folios(unsigned long
*isolate_scanned = scanned;
break;
}
-
- type = !type;
+ /*
+ * If scanned > 0 and isolated == 0, avoid falling back to the
+ * other type, as this type remains sufficient. Falling back
+ * too readily can disrupt the positive_ctrl_err() bias.
+ */
+ if (!scanned)
+ type = !type;
}
return total_scanned;
@@ -4909,18 +4914,14 @@ static long get_nr_to_scan(struct lruvec
unsigned long nr_to_scan, evictable;
evictable = lruvec_evictable_size(lruvec, swappiness);
- nr_to_scan = evictable;
/* try to scrape all its memory if this memcg was deleted */
if (!mem_cgroup_online(memcg))
- return nr_to_scan;
+ return evictable;
- nr_to_scan = apply_proportional_protection(memcg, sc, nr_to_scan);
+ nr_to_scan = apply_proportional_protection(memcg, sc, evictable);
nr_to_scan >>= sc->priority;
- if (!nr_to_scan && sc->priority < DEF_PRIORITY)
- nr_to_scan = min(evictable, SWAP_CLUSTER_MAX);
-
return nr_to_scan;
}
_
^ permalink raw reply [flat|nested] 18+ messages in thread