mm/vmscan: fix swappiness=max and clean up per-node proactive reclaim
Subsystems (3)
cover mm/vmscan: fix swappiness=max and clean up per-node proactive reclaim
From: Ridong Chen <[email protected]>
Two fixes and one cleanup.
Patch 1 fixes "swappiness=max": the anon-only test in get_scan_count() sat after the "cannot reclaim anon" check, so when no anon was reclaimable the request fell back to SCAN_FILE and evicted page cache instead.
Patch 2 fixes reclaim_store() collapsing every error into -EAGAIN, so callers can no longer tell an invalid argument from a busy interface; propagate the real error code, matching the memcg path.
Patch 3 drops the now-unused gfp_mask parameter from __node_reclaim().
Ridong Chen (3):
mm/vmscan: fix anon-only reclaim evicting file pages when
swappiness=max
mm: vmscan: propagate real error code from per-node proactive reclaim
mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()
mm/vmscan.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-)
Signature · 1 line
2.34.1
PATCH 1/3 mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max
From: Ridong Chen <[email protected]>
As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks in get_scan_count(), file pages may still be evicted if can_reclaim_anon_pages() returns false, which contradicts the semantics of SWAPPINESS_ANON_ONLY.
Reproducer in a cgroup holding 64M of file cache, with no swap configured:
Before (file cache is wrongly evicted):
# cat memory.stat
anon 196608
file 67178496
pgscan_proactive 0
# echo "64M swappiness=max" > memory.reclaim
# cat memory.stat
anon 208896
file 4096 <- page cache evicted
pgsteal_proactive 16400
pgscan_proactive 16400After (file cache is left intact):
# cat memory.stat
anon 200704
file 67178496
pgscan_proactive 0
# echo "64M swappiness=max" > memory.reclaim
-bash: echo: write error: Resource temporarily unavailable
# cat memory.stat
anon 208896
file 67178496 <- page cache untouched
pgsteal_proactive 0
pgscan_proactive 0Fix this by bailing out early when SWAPPINESS_ANON_ONLY is set and no anonymous pages are reclaimable, before falling back to file reclaim.
[1] https://lore.kernel.org/cgroups/[email protected]/
--- mm/vmscan.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
mm/vmscan.c +11 -7
@@ -2492,6 +2492,17 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,enum scan_balance scan_balance;enum lru_list lru; +/* Proactive reclaim initiated by userspace for anonymous memory only */ +if (swappiness ==SWAPPINESS_ANON_ONLY ) { +WARN_ON_ONCE (!sc->proactive); +if (!can_reclaim_anon_pages (memcg, pgdat->node_id, sc)) { +memset (nr,0 ,sizeof (*nr) *NR_LRU_LISTS ); +return ; + } + scan_balance =SCAN_ANON ; + goto out; + } +/* If we have no swap space, do not bother scanning anon folios. */ if (!sc->may_swap || !can_reclaim_anon_pages (memcg, pgdat->node_id, sc)) { scan_balance =SCAN_FILE ;
@@ -2510,13 +2521,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, goto out; } -/* Proactive reclaim initiated by userspace for anonymous memory only */ -if (swappiness ==SWAPPINESS_ANON_ONLY ) { -WARN_ON_ONCE (!sc->proactive); - scan_balance =SCAN_ANON ; - goto out; - } -/* * Do not apply any pressure balancing cleverness when the * system is close to OOM, scan both anon and file equally
Signature · 1 line
2.34.1
Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max
Quoted 35 lines · Ridong
From: Ridong Chen <[email protected]>
As Qi mentioned [1], when swappiness=max (
SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks inget_scan_count(), file pages may still be evicted ifcan_reclaim_anon_pages()returns false, which contradicts the semantics ofSWAPPINESS_ANON_ONLY.Reproducer in a cgroup holding 64M of file cache, with no swap configured:
Before (file cache is wrongly evicted):
# cat memory.stat anon 196608 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 4096 <- page cache evicted pgsteal_proactive 16400 pgscan_proactive 16400After (file cache is left intact):
# cat memory.stat anon 200704 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 208896 file 67178496 <- page cache untouched pgsteal_proactive 0 pgscan_proactive 0
Quoted 8 lines
Fix this by bailing out early when
SWAPPINESS_ANON_ONLYis set and no anonymous pages are reclaimable, before falling back to file reclaim.[1] https://lore.kernel.org/cgroups/[email protected]/
Fixes 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")Suggested-by Qi Zheng <[email protected]>Signed-off-by Ridong Chen <[email protected]>
Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max
In reply to RidongQuoted 39 lines · Ridong
From: Ridong Chen <[email protected]>
As Qi mentioned [1], when swappiness=max (
SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks inget_scan_count(), file pages may still be evicted ifcan_reclaim_anon_pages()returns false, which contradicts the semantics ofSWAPPINESS_ANON_ONLY.Reproducer in a cgroup holding 64M of file cache, with no swap configured:
Before (file cache is wrongly evicted):
# cat memory.stat anon 196608 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 4096 <- page cache evicted pgsteal_proactive 16400 pgscan_proactive 16400After (file cache is left intact):
# cat memory.stat anon 200704 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 208896 file 67178496 <- page cache untouched pgsteal_proactive 0 pgscan_proactive 0
Quoted 8 lines
Fix this by bailing out early when
SWAPPINESS_ANON_ONLYis set and no anonymous pages are reclaimable, before falling back to file reclaim.[1] https://lore.kernel.org/cgroups/[email protected]/
Fixes 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")Suggested-by Qi Zheng <[email protected]>Signed-off-by Ridong Chen <[email protected]>
Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max
In reply to RidongQuoted 35 lines · Ridong
From: Ridong Chen <[email protected]>
As Qi mentioned [1], when swappiness=max (
SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks inget_scan_count(), file pages may still be evicted ifcan_reclaim_anon_pages()returns false, which contradicts the semantics ofSWAPPINESS_ANON_ONLY.Reproducer in a cgroup holding 64M of file cache, with no swap configured:
Before (file cache is wrongly evicted):
# cat memory.stat anon 196608 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 4096 <- page cache evicted pgsteal_proactive 16400 pgscan_proactive 16400After (file cache is left intact):
# cat memory.stat anon 200704 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 208896 file 67178496 <- page cache untouched pgsteal_proactive 0 pgscan_proactive 0
Quoted 8 lines
Fix this by bailing out early when
SWAPPINESS_ANON_ONLYis set and no anonymous pages are reclaimable, before falling back to file reclaim.[1] https://lore.kernel.org/cgroups/[email protected]/
Fixes 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")Suggested-by Qi Zheng <[email protected]>Signed-off-by Ridong Chen <[email protected]>
PATCH 2/3 mm: vmscan: propagate real error code from per-node proactive reclaim
In reply to RidongFrom: Ridong Chen <[email protected]>
It has been observed that per-node proactive reclaim always returns -EAGAIN when any error occurs. As discussed in the mailing list [1], the interface should distinguish between cases where no reclaimable memory is left and where another entity is concurrently using the same interface. Propagate the real error code, consistent with how memcg proactive reclaim handles errors.
--- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
mm/vmscan.c +1 -1
@@ -8008,7 +8008,7 @@ static ssize_t reclaim_store(struct device *dev,int ret, nid = dev->id; ret =user_proactive_reclaim ((char *)buf,NULL ,NODE_DATA (nid)); -return ret ? -EAGAIN : count; +return ret ? ret : count; }static DEVICE_ATTR_WO (reclaim);
Signature · 1 line
2.34.1
Re: [PATCH 2/3] mm: vmscan: propagate real error code from per-node proactive reclaim
Quoted 9 lines · Ridong
From: Ridong Chen <[email protected]>
It has been observed that per-node proactive reclaim always returns
-EAGAINwhen any error occurs. As discussed in the mailing list [1], the interface should distinguish between cases where no reclaimable memory is left and where another entity is concurrently using the same interface. Propagate the real error code, consistent with how memcg proactive reclaim handles errors.
Quoted 4 lines
Fixes b980077899ea ("mm: introduce per-node proactive reclaim interface")Signed-off-by Ridong Chen <[email protected]>
Re: [PATCH 2/3] mm: vmscan: propagate real error code from per-node proactive reclaim
In reply to RidongQuoted 13 lines · Ridong
From: Ridong Chen <[email protected]>
It has been observed that per-node proactive reclaim always returns
-EAGAINwhen any error occurs. As discussed in the mailing list [1], the interface should distinguish between cases where no reclaimable memory is left and where another entity is concurrently using the same interface. Propagate the real error code, consistent with how memcg proactive reclaim handles errors.
Quoted 4 lines
Fixes b980077899ea ("mm: introduce per-node proactive reclaim interface")Signed-off-by Ridong Chen <[email protected]>
Quoted 9 lines
---
mm/vmscan.c| 2 +-1 file changed, 1 insertion(+), 1 deletion(-)mm/vmscan.c +0
-0
mm/vmscan.c static ssize_t reclaim_store(struct device *dev, · line 8011
Quoted 5 lines
mm/vmscan.c +1
-1@@ -8008,7 +8008,7 @@ static ssize_t reclaim_store(struct device *dev,int ret, nid = dev->id; ret =user_proactive_reclaim ((char *)buf,NULL ,NODE_DATA (nid)); -return ret ? -EAGAIN : count; +return ret ? ret : count;
I usually use "? :" to omit ret. Just to be clear, I'm only sharing this as a personal preference. I'm not suggesting that you actually need to change it.
Quoted 6 lines
mm/vmscan.c +0
-0}static DEVICE_ATTR_WO (reclaim);Signature · 1 line
2.34.1
Re: [PATCH 2/3] mm: vmscan: propagate real error code from per-node proactive reclaim
In reply to RidongQuoted 9 lines · Ridong
From: Ridong Chen <[email protected]>
It has been observed that per-node proactive reclaim always returns
-EAGAINwhen any error occurs. As discussed in the mailing list [1], the interface should distinguish between cases where no reclaimable memory is left and where another entity is concurrently using the same interface. Propagate the real error code, consistent with how memcg proactive reclaim handles errors.
Quoted 4 lines
Fixes b980077899ea ("mm: introduce per-node proactive reclaim interface")Signed-off-by Ridong Chen <[email protected]>
PATCH 3/3 mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()
In reply to RidongFrom: Ridong Chen <[email protected]>
Commit 57972c78e678 ("mm/vmscan: make __node_reclaim() more generic") moved the scan_control construction out to the callers and passed the struct in by pointer. After that change every use of the gfp mask inside __node_reclaim() goes through sc->gfp_mask, leaving the gfp_mask parameter unused. Just remove the dead parameter and update the callers accordingly. No functional change.
--- mm/vmscan.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
mm/vmscan.c +4 -5
@@ -7729,7 +7729,7 @@ static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)/* * Try to free up some pages from this node through reclaim. */ -static unsigned long __node_reclaim (struct pglist_data *pgdat,gfp_t gfp_mask, +static unsigned long __node_reclaim (struct pglist_data *pgdat,unsigned long nr_pages,struct scan_control *sc) {
@@ -7821,7 +7821,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)if (test_and_set_bit_lock (PGDAT_RECLAIM_LOCKED , &pgdat->flags))return NODE_RECLAIM_NOSCAN ; - ret =__node_reclaim (pgdat, gfp_mask, nr_pages, &sc) >= nr_pages; + ret =__node_reclaim (pgdat, nr_pages, &sc) >= nr_pages;clear_bit_unlock (PGDAT_RECLAIM_LOCKED , &pgdat->flags);if (ret)
@@ -7834,7 +7834,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)#else -static unsigned long __node_reclaim (struct pglist_data *pgdat,gfp_t gfp_mask, +static unsigned long __node_reclaim (struct pglist_data *pgdat,unsigned long nr_pages,struct scan_control *sc) {
@@ -7940,8 +7940,7 @@ int user_proactive_reclaim(char *buf, &pgdat->flags))return -EBUSY ; - reclaimed =__node_reclaim (pgdat, gfp_mask, - batch_size, &sc); + reclaimed =__node_reclaim (pgdat, batch_size, &sc);clear_bit_unlock (PGDAT_RECLAIM_LOCKED , &pgdat->flags); }
Signature · 1 line
2.34.1
Re: [PATCH 3/3] mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()
Quoted 10 lines · Ridong
From: Ridong Chen <[email protected]>
Commit
57972c78e678("mm/vmscan: make__node_reclaim()more generic") moved thescan_controlconstruction out to the callers and passed the struct in by pointer. After that change every use of the gfp mask inside__node_reclaim()goes throughsc->gfp_mask, leaving thegfp_maskparameter unused. Just remove the dead parameter and update the callers accordingly. No functional change.Signed-off-by Ridong Chen <[email protected]>
Re: [PATCH 3/3] mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()
In reply to RidongQuoted 14 lines · Ridong
From: Ridong Chen <[email protected]>
Commit
57972c78e678("mm/vmscan: make__node_reclaim()more generic") moved thescan_controlconstruction out to the callers and passed the struct in by pointer. After that change every use of the gfp mask inside__node_reclaim()goes throughsc->gfp_mask, leaving thegfp_maskparameter unused. Just remove the dead parameter and update the callers accordingly. No functional change.Signed-off-by Ridong Chen <[email protected]>
Re: [PATCH 3/3] mm: vmscan: drop unused gfp_mask parameter from __node_reclaim()
In reply to RidongQuoted 10 lines · Ridong
From: Ridong Chen <[email protected]>
Commit
57972c78e678("mm/vmscan: make__node_reclaim()more generic") moved thescan_controlconstruction out to the callers and passed the struct in by pointer. After that change every use of the gfp mask inside__node_reclaim()goes throughsc->gfp_mask, leaving thegfp_maskparameter unused. Just remove the dead parameter and update the callers accordingly. No functional change.Signed-off-by Ridong Chen <[email protected]>
Andrew Morton
maintainerQuoted 9 lines · On Fri, 17 Jul 2026 19:32:57 +0800 Ridong <[email protected]> wrote:
From: Ridong Chen <[email protected]>
Two fixes and one cleanup.
Patch 1 fixes "swappiness=max": the anon-only test in
get_scan_count()sat after the "cannot reclaim anon" check, so when no anon was reclaimable the request fell back toSCAN_FILEand evicted page cache instead.
Quoted 5 lines
Patch 2 fixes
reclaim_store()collapsing every error into-EAGAIN, so callers can no longer tell an invalid argument from a busy interface; propagate the real error code, matching the memcg path.Patch 3 drops the now-unused
gfp_maskparameter from__node_reclaim().
Thanks. Sashiko want to know whether MGLRU should also be fixed:
https://sashiko.dev/#/patchset/[email protected]
Quoted 11 lines · Andrew Morton
Quoted 9 lines · On Fri, 17 Jul 2026 19:32:57 +0800 Ridong <[email protected]> wrote:
From: Ridong Chen <[email protected]>
Two fixes and one cleanup.
Patch 1 fixes "swappiness=max": the anon-only test in
get_scan_count()sat after the "cannot reclaim anon" check, so when no anon was reclaimable the request fell back toSCAN_FILEand evicted page cache instead.
Quoted 9 lines
Quoted 5 lines
Patch 2 fixes
reclaim_store()collapsing every error into-EAGAIN, so callers can no longer tell an invalid argument from a busy interface; propagate the real error code, matching the memcg path.Patch 3 drops the now-unused
gfp_maskparameter from__node_reclaim().Thanks. Sashiko want to know whether MGLRU should also be fixed:
https://sashiko.dev/#/patchset/[email protected]
Yes, it should be fixed. I will add a patch to fix it.
Signature · 2 lines
Best regards, Ridong