* + mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch added to mm-new branch
@ 2026-04-27 18:23 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-27 18:23 UTC (permalink / raw)
To: mm-commits, kasong, akpm
The patch titled
Subject: mm/vmscan: unify writeback reclaim statistic and throttling
has been added to the -mm mm-new branch. Its filename is
mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
This patch will later appear in the mm-new branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews. Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.
The mm-new branch of mm.git is not included in linux-next
If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm/vmscan: unify writeback reclaim statistic and throttling
Date: Tue, 28 Apr 2026 02:07:06 +0800
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.
Link: https://lore.kernel.org/20260428-mglru-reclaim-v7-15-02fabb92dc43@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
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>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Stevens <stevensd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yafang <laoar.shao@gmail.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/vmscan.c | 92 +++++++++++++++++++++++---------------------------
1 file changed, 43 insertions(+), 49 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-unify-writeback-reclaim-statistic-and-throttling
+++ a/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_lis
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
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 @@ retry:
if (!list_empty(&list)) {
skip_retry = true;
+ isolated = 0;
goto retry;
}
_
Patches currently in -mm which might be from kasong@tencent.com are
mm-mglru-consolidate-common-code-for-retrieving-evictable-size.patch
mm-mglru-rename-variables-related-to-aging-and-rotation.patch
mm-mglru-relocate-the-lru-scan-batch-limit-to-callers.patch
mm-mglru-restructure-the-reclaim-loop.patch
mm-mglru-scan-and-count-the-exact-number-of-folios.patch
mm-mglru-use-a-smaller-batch-for-reclaim.patch
mm-mglru-dont-abort-scan-immediately-right-after-aging.patch
mm-mglru-remove-redundant-swap-constrained-check-upon-isolation.patch
mm-mglru-use-the-common-routine-for-dirty-writeback-reactivation.patch
mm-mglru-simplify-and-improve-dirty-writeback-handling.patch
mm-mglru-remove-no-longer-used-reclaim-argument-for-folio-protection.patch
mm-vmscan-remove-sc-file_taken.patch
mm-vmscan-remove-sc-unqueued_dirty.patch
mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch added to mm-new branch
@ 2026-04-23 18:14 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-04-23 18:14 UTC (permalink / raw)
To: mm-commits, kasong, akpm
The patch titled
Subject: mm/vmscan: unify writeback reclaim statistic and throttling
has been added to the -mm mm-new branch. Its filename is
mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
This patch will later appear in the mm-new branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews. Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.
The mm-new branch of mm.git is not included in linux-next
If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm/vmscan: unify writeback reclaim statistic and throttling
Date: Fri, 24 Apr 2026 01:43:25 +0800
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 looking good.
Global throttling is not here yet, we will fix that separately later.
Link: https://lore.kernel.org/20260424-mglru-reclaim-v6-14-a57622d770c3@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
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>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Stevens <stevensd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yafang <laoar.shao@gmail.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/vmscan.c | 92 +++++++++++++++++++++++---------------------------
1 file changed, 43 insertions(+), 49 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-unify-writeback-reclaim-statistic-and-throttling
+++ a/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_lis
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;
@@ -4824,26 +4830,13 @@ static int evict_folios(unsigned long nr
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);
@@ -4886,6 +4879,7 @@ retry:
if (!list_empty(&list)) {
skip_retry = true;
+ isolated = 0;
goto retry;
}
_
Patches currently in -mm which might be from kasong@tencent.com are
mm-mglru-consolidate-common-code-for-retrieving-evictable-size.patch
mm-mglru-rename-variables-related-to-aging-and-rotation.patch
mm-mglru-relocate-the-lru-scan-batch-limit-to-callers.patch
mm-mglru-restructure-the-reclaim-loop.patch
mm-mglru-scan-and-count-the-exact-number-of-folios.patch
mm-mglru-use-a-smaller-batch-for-reclaim.patch
mm-mglru-dont-abort-scan-immediately-right-after-aging.patch
mm-mglru-remove-redundant-swap-constrained-check-upon-isolation.patch
mm-mglru-use-the-common-routine-for-dirty-writeback-reactivation.patch
mm-mglru-simplify-and-improve-dirty-writeback-handling.patch
mm-mglru-remove-no-longer-used-reclaim-argument-for-folio-protection.patch
mm-vmscan-remove-sc-file_taken.patch
mm-vmscan-remove-sc-unqueued_dirty.patch
mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-04-27 18:23 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-04-27 18:23 + mm-vmscan-unify-writeback-reclaim-statistic-and-throttling.patch added to mm-new branch Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2026-04-23 18:14 Andrew Morton
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.