[PATCH V4 0/4] add max arg to swappiness in memory.reclaim and lru_gen

[PATCH V4 0/4] add max arg to swappiness in memory.reclaim and lru_gen

[Zhongkun He]

This patchset add max arg to swappiness in memory.reclaim and lru_gen
for anon only proactive memory reclaim.

With the patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
memory.reclaim")', we can submit an additional swappiness=<val> argument
to memory.reclaim. It is very useful because we can dynamically adjust
the reclamation ratio based on the anonymous folios and file folios of
each cgroup. For example,when swappiness is set to 0, we only reclaim
from file folios. But we can not relciam memory just from anon folios.

This patch introduces a new macro, SWAPPINESS_ANON_ONLY, defined as
MAX_SWAPPINESS + 1, represent the max arg semantics. It specifically
indicates that reclamation should occur only from anonymous pages.

Patch 1 add swappiness=max arg to memory.reclaim
suggested-by: Yosry Ahmed

Patch 2 add more comments for cache_trim_mode from
Johannes Weiner in [1].

Patch 3 add max arg to lru_gen for proactive memory reclaim in MGLRU.
The MGLRU already supports reclaiming exclusively from anonymous pages.
This patch formalizes that behavior by introducing a max parameter to
represent the corresponding semantics.

Patch 4 using SWAPPINESS_ANON_ONLY in MGLRU
Using SWAPPINESS_ANON_ONLY instead of MAX_SWAPPINESS + 1
to indicate reclaiming only from anonymous pages makes the
code more readable and explicit

[1]:
https://lore.kernel.org/all/20250314141833.GA1316033@cmpxchg.org/

Here is the previous discussion:
https://lore.kernel.org/all/20250314033350.1156370-1-hezhongkun.hzk@bytedance.com/
https://lore.kernel.org/all/20250312094337.2296278-1-hezhongkun.hzk@bytedance.com/
https://lore.kernel.org/all/20250318135330.3358345-1-hezhongkun.hzk@bytedance.com/

V4:
Split the patch in MGLRU and add comments to make the code clearer
from Andrew Morton.

V3:
In MGLRU, add max swappiness arg to lru_gen for proactive memory reclaim. 
Add the use of SWAPPINESS_ANON_ONLY in place of 'MAX_SWAPPINESS + 1' to
improves code clarity and makes the intention more explicit.

Add more comments about cache_trim_mode.

V2:
Add max arg to swappiness as the mode of reclaim from anon memory only
in memory.reclaim.



Zhongkun He (4):
  mm: add swappiness=max arg to memory.reclaim for only anon reclaim
  mm: vmscan: add more comments about cache_trim_mode
  mm: add max swappiness arg to lru_gen for anonymous memory only
  mm: using SWAPPINESS_ANON_ONLY in MGLRU

 Documentation/admin-guide/cgroup-v2.rst       |  3 ++
 Documentation/admin-guide/mm/multigen_lru.rst |  5 ++-
 include/linux/swap.h                          |  4 ++
 mm/memcontrol.c                               |  5 +++
 mm/vmscan.c                                   | 42 +++++++++++++++----
 5 files changed, 49 insertions(+), 10 deletions(-)

-- 
2.39.5

[PATCH V4 1/4] mm: add swappiness=max arg to memory.reclaim for only anon reclaim

[Zhongkun He]

With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
memory.reclaim")', we can submit an additional swappiness=<val> argument
to memory.reclaim. It is very useful because we can dynamically adjust
the reclamation ratio based on the anonymous folios and file folios of
each cgroup. For example,when swappiness is set to 0, we only reclaim
from file folios.

However,we have also encountered a new issue: when swappiness is set to
the MAX_SWAPPINESS, it may still only reclaim file folios.

So, we hope to add a new arg 'swappiness=max' in memory.reclaim where
proactive memory reclaim only reclaims from anonymous folios when
swappiness is set to max. The swappiness semantics from a user
perspective remain unchanged.

For example, something like this:

echo "2M swappiness=max" > /sys/fs/cgroup/memory.reclaim

will perform reclaim on the rootcg with a swappiness setting of 'max' (a
new mode) regardless of the file folios. Users have a more comprehensive
view of the application's memory distribution because there are many
metrics available. For example, if we find that a certain cgroup has a
large number of inactive anon folios, we can reclaim only those and skip
file folios, because with the zram/zswap, the IO tradeoff that
cache_trim_mode or other file first logic is making doesn't hold -
file refaults will cause IO, whereas anon decompression will not.

With this patch, the swappiness argument of memory.reclaim has a new
mode 'max', means reclaiming just from anonymous folios both in traditional
LRU and MGLRU.

Here is the previous discussion:
https://lore.kernel.org/all/20250314033350.1156370-1-hezhongkun.hzk@bytedance.com/
https://lore.kernel.org/all/20250312094337.2296278-1-hezhongkun.hzk@bytedance.com/
https://lore.kernel.org/all/20250318135330.3358345-1-hezhongkun.hzk@bytedance.com/

Suggested-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 3 +++
 include/linux/swap.h                    | 4 ++++
 mm/memcontrol.c                         | 5 +++++
 mm/vmscan.c                             | 7 +++++++
 4 files changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..472c01e0eb2c 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1348,6 +1348,9 @@ The following nested keys are defined.
 	same semantics as vm.swappiness applied to memcg reclaim with
 	all the existing limitations and potential future extensions.
 
+	The valid range for swappiness is [0-200, max], setting
+	swappiness=max exclusively reclaims anonymous memory.
+
   memory.peak
 	A read-write single value file which exists on non-root cgroups.
 
diff --git a/include/linux/swap.h b/include/linux/swap.h
index db46b25a65ae..f57c7e0012ba 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -414,6 +414,10 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 #define MEMCG_RECLAIM_PROACTIVE (1 << 2)
 #define MIN_SWAPPINESS 0
 #define MAX_SWAPPINESS 200
+
+/* Just recliam from anon folios in proactive memory reclaim */
+#define SWAPPINESS_ANON_ONLY (MAX_SWAPPINESS + 1)
+
 extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 						  unsigned long nr_pages,
 						  gfp_t gfp_mask,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c96c1f2b9cf5..796c78b26e43 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4395,11 +4395,13 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
 
 enum {
 	MEMORY_RECLAIM_SWAPPINESS = 0,
+	MEMORY_RECLAIM_SWAPPINESS_MAX,
 	MEMORY_RECLAIM_NULL,
 };
 
 static const match_table_t tokens = {
 	{ MEMORY_RECLAIM_SWAPPINESS, "swappiness=%d"},
+	{ MEMORY_RECLAIM_SWAPPINESS_MAX, "swappiness=max"},
 	{ MEMORY_RECLAIM_NULL, NULL },
 };
 
@@ -4433,6 +4435,9 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
 			if (swappiness < MIN_SWAPPINESS || swappiness > MAX_SWAPPINESS)
 				return -EINVAL;
 			break;
+		case MEMORY_RECLAIM_SWAPPINESS_MAX:
+			swappiness = SWAPPINESS_ANON_ONLY;
+			break;
 		default:
 			return -EINVAL;
 		}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3783e45bfc92..ebe1407f6741 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2503,6 +2503,13 @@ 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
-- 
2.39.5

[PATCH V4 2/4] mm: vmscan: add more comments about cache_trim_mode

[Zhongkun He]

Add more comments for cache_trim_mode, and the annotations
provided by Johannes Weiner in [1].

[1]:
https://lore.kernel.org/all/20250314141833.GA1316033@cmpxchg.org/

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 mm/vmscan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ebe1407f6741..49eb2a4e490d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2530,7 +2530,8 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 
 	/*
 	 * If there is enough inactive page cache, we do not reclaim
-	 * anything from the anonymous working right now.
+	 * anything from the anonymous working right now to make sure
+         * a streaming file access pattern doesn't cause swapping.
 	 */
 	if (sc->cache_trim_mode) {
 		scan_balance = SCAN_FILE;
-- 
2.39.5

[PATCH V4 3/4] mm: add max swappiness arg to lru_gen for anonymous memory only

[Zhongkun He]

The MGLRU already supports reclaiming only from anonymous memory
via the /sys/kernel/debug/lru_gen interface. Now, memory.reclaim
also supports the swappiness=max parameter to enable reclaiming
solely from anonymous memory. To unify the semantics of proactive
reclaiming from anonymous folios, the max parameter is introduced.

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 Documentation/admin-guide/mm/multigen_lru.rst |  5 +++--
 mm/vmscan.c                                   | 15 ++++++++++++---
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/admin-guide/mm/multigen_lru.rst
index 33e068830497..9cb54b4ff5d9 100644
--- a/Documentation/admin-guide/mm/multigen_lru.rst
+++ b/Documentation/admin-guide/mm/multigen_lru.rst
@@ -151,8 +151,9 @@ generations less than or equal to ``min_gen_nr``.
 ``min_gen_nr`` should be less than ``max_gen_nr-1``, since
 ``max_gen_nr`` and ``max_gen_nr-1`` are not fully aged (equivalent to
 the active list) and therefore cannot be evicted. ``swappiness``
-overrides the default value in ``/proc/sys/vm/swappiness``.
-``nr_to_reclaim`` limits the number of pages to evict.
+overrides the default value in ``/proc/sys/vm/swappiness`` and the valid
+range is [0-200, max], with max being exclusively used for the reclamation
+of anonymous memory. ``nr_to_reclaim`` limits the number of pages to evict.
 
 A typical use case is that a job scheduler runs this command before it
 tries to land a new job on a server. If it fails to materialize enough
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 49eb2a4e490d..b442c20d1168 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5581,7 +5581,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
 	while ((cur = strsep(&next, ",;\n"))) {
 		int n;
 		int end;
-		char cmd;
+		char cmd, swap_string[5];
 		unsigned int memcg_id;
 		unsigned int nid;
 		unsigned long seq;
@@ -5592,13 +5592,22 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
 		if (!*cur)
 			continue;
 
-		n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
-			   &seq, &end, &swappiness, &end, &opt, &end);
+		n = sscanf(cur, "%c %u %u %lu %n %4s %n %lu %n", &cmd, &memcg_id, &nid,
+			   &seq, &end, swap_string, &end, &opt, &end);
 		if (n < 4 || cur[end]) {
 			err = -EINVAL;
 			break;
 		}
 
+		/* set by userspace for anonymous memory only */
+		if (!strncmp("max", swap_string, sizeof("max"))) {
+			swappiness = SWAPPINESS_ANON_ONLY;
+		} else {
+			err = kstrtouint(swap_string, 0, &swappiness);
+			if (err)
+				break;
+		}
+
 		err = run_cmd(cmd, memcg_id, nid, seq, &sc, swappiness, opt);
 		if (err)
 			break;
-- 
2.39.5

[PATCH V4 4/4] mm: using SWAPPINESS_ANON_ONLY in MGLRU

[Zhongkun He]

Using SWAPPINESS_ANON_ONLY instead of MAX_SWAPPINESS + 1
to indicate reclaiming only from anonymous pages makes the
code more readable and explicit.

Add some comment in the SWAPPINESS_ANON_ONLY context.

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 mm/vmscan.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b442c20d1168..24e959881ada 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2698,8 +2698,12 @@ static bool should_clear_pmd_young(void)
 		READ_ONCE((lruvec)->lrugen.min_seq[LRU_GEN_FILE]),	\
 	}
 
+/* Get the min/max evictable type based on swappiness */
+#define min_type(swappiness) (!(swappiness))
+#define max_type(swappiness) ((swappiness) < SWAPPINESS_ANON_ONLY)
+
 #define evictable_min_seq(min_seq, swappiness)				\
-	min((min_seq)[!(swappiness)], (min_seq)[(swappiness) <= MAX_SWAPPINESS])
+	min((min_seq)[min_type(swappiness)], (min_seq)[max_type(swappiness)])
 
 #define for_each_gen_type_zone(gen, type, zone)				\
 	for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++)			\
@@ -2707,7 +2711,7 @@ static bool should_clear_pmd_young(void)
 			for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++)
 
 #define for_each_evictable_type(type, swappiness)			\
-	for ((type) = !(swappiness); (type) <= ((swappiness) <= MAX_SWAPPINESS); (type)++)
+	for ((type) = min_type(swappiness); (type) <= max_type(swappiness); (type)++)
 
 #define get_memcg_gen(seq)	((seq) % MEMCG_NR_GENS)
 #define get_memcg_bin(bin)	((bin) % MEMCG_NR_BINS)
@@ -3858,7 +3862,12 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 	int hist = lru_hist_from_seq(lrugen->min_seq[type]);
 	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
 
-	if (type ? swappiness > MAX_SWAPPINESS : !swappiness)
+	/* For file type, skip the check if swappiness is anon only */
+	if (type && (swappiness == SWAPPINESS_ANON_ONLY))
+		goto done;
+
+	/* For anon type, skip the check if swappiness is zero (file only) */
+	if (!type && !swappiness)
 		goto done;
 
 	/* prevent cold/hot inversion if the type is evictable */
@@ -5524,7 +5533,7 @@ static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,
 
 	if (swappiness < MIN_SWAPPINESS)
 		swappiness = get_swappiness(lruvec, sc);
-	else if (swappiness > MAX_SWAPPINESS + 1)
+	else if (swappiness > SWAPPINESS_ANON_ONLY)
 		goto done;
 
 	switch (cmd) {
-- 
2.39.5

Re: [PATCH V4 1/4] mm: add swappiness=max arg to memory.reclaim for only anon reclaim

[Muchun Song]

> On Apr 21, 2025, at 17:13, Zhongkun He <hezhongkun.hzk@bytedance.com> wrote:
> 
> With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
> memory.reclaim")', we can submit an additional swappiness=<val> argument
> to memory.reclaim. It is very useful because we can dynamically adjust
> the reclamation ratio based on the anonymous folios and file folios of
> each cgroup. For example,when swappiness is set to 0, we only reclaim
> from file folios.
> 
> However,we have also encountered a new issue: when swappiness is set to
> the MAX_SWAPPINESS, it may still only reclaim file folios.
> 
> So, we hope to add a new arg 'swappiness=max' in memory.reclaim where
> proactive memory reclaim only reclaims from anonymous folios when
> swappiness is set to max. The swappiness semantics from a user
> perspective remain unchanged.
> 
> For example, something like this:
> 
> echo "2M swappiness=max" > /sys/fs/cgroup/memory.reclaim

We already have this kind of style (mixing numbers and strings) within
io.max under cgroup v2. As a result, I'm okay with this change. 

> 
> will perform reclaim on the rootcg with a swappiness setting of 'max' (a
> new mode) regardless of the file folios. Users have a more comprehensive
> view of the application's memory distribution because there are many
> metrics available. For example, if we find that a certain cgroup has a
> large number of inactive anon folios, we can reclaim only those and skip
> file folios, because with the zram/zswap, the IO tradeoff that
> cache_trim_mode or other file first logic is making doesn't hold -
> file refaults will cause IO, whereas anon decompression will not.
> 
> With this patch, the swappiness argument of memory.reclaim has a new
> mode 'max', means reclaiming just from anonymous folios both in traditional
> LRU and MGLRU.
> 
> Here is the previous discussion:
> https://lore.kernel.org/all/20250314033350.1156370-1-hezhongkun.hzk@bytedance.com/
> https://lore.kernel.org/all/20250312094337.2296278-1-hezhongkun.hzk@bytedance.com/
> https://lore.kernel.org/all/20250318135330.3358345-1-hezhongkun.hzk@bytedance.com/
> 
> Suggested-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.

Re: [PATCH V4 3/4] mm: add max swappiness arg to lru_gen for anonymous memory only

[Muchun Song]

> On Apr 21, 2025, at 17:13, Zhongkun He <hezhongkun.hzk@bytedance.com> wrote:
> 
> The MGLRU already supports reclaiming only from anonymous memory
> via the /sys/kernel/debug/lru_gen interface. Now, memory.reclaim
> also supports the swappiness=max parameter to enable reclaiming
> solely from anonymous memory. To unify the semantics of proactive
> reclaiming from anonymous folios, the max parameter is introduced.
> 
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.

Re: [External] Re: [PATCH V4 1/4] mm: add swappiness=max arg to memory.reclaim for only anon reclaim

[Zhongkun He]

On Mon, Apr 21, 2025 at 5:35 PM Muchun Song <muchun.song@linux.dev> wrote:
>
>
>
> > On Apr 21, 2025, at 17:13, Zhongkun He <hezhongkun.hzk@bytedance.com> wrote:
> >
> > With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
> > memory.reclaim")', we can submit an additional swappiness=<val> argument
> > to memory.reclaim. It is very useful because we can dynamically adjust
> > the reclamation ratio based on the anonymous folios and file folios of
> > each cgroup. For example,when swappiness is set to 0, we only reclaim
> > from file folios.
> >
> > However,we have also encountered a new issue: when swappiness is set to
> > the MAX_SWAPPINESS, it may still only reclaim file folios.
> >
> > So, we hope to add a new arg 'swappiness=max' in memory.reclaim where
> > proactive memory reclaim only reclaims from anonymous folios when
> > swappiness is set to max. The swappiness semantics from a user
> > perspective remain unchanged.
> >
> > For example, something like this:
> >
> > echo "2M swappiness=max" > /sys/fs/cgroup/memory.reclaim
>
> We already have this kind of style (mixing numbers and strings) within
> io.max under cgroup v2. As a result, I'm okay with this change.
>
> >
> > will perform reclaim on the rootcg with a swappiness setting of 'max' (a
> > new mode) regardless of the file folios. Users have a more comprehensive
> > view of the application's memory distribution because there are many
> > metrics available. For example, if we find that a certain cgroup has a
> > large number of inactive anon folios, we can reclaim only those and skip
> > file folios, because with the zram/zswap, the IO tradeoff that
> > cache_trim_mode or other file first logic is making doesn't hold -
> > file refaults will cause IO, whereas anon decompression will not.
> >
> > With this patch, the swappiness argument of memory.reclaim has a new
> > mode 'max', means reclaiming just from anonymous folios both in traditional
> > LRU and MGLRU.
> >
> > Here is the previous discussion:
> > https://lore.kernel.org/all/20250314033350.1156370-1-hezhongkun.hzk@bytedance.com/
> > https://lore.kernel.org/all/20250312094337.2296278-1-hezhongkun.hzk@bytedance.com/
> > https://lore.kernel.org/all/20250318135330.3358345-1-hezhongkun.hzk@bytedance.com/
> >
> > Suggested-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> > Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
>
> Acked-by: Muchun Song <muchun.song@linux.dev>

Thank you for your time, Muchun.

>
> Thanks.

Re: [External] Re: [PATCH V4 3/4] mm: add max swappiness arg to lru_gen for anonymous memory only

[Zhongkun He]

On Mon, Apr 21, 2025 at 5:36 PM Muchun Song <muchun.song@linux.dev> wrote:
>
>
>
> > On Apr 21, 2025, at 17:13, Zhongkun He <hezhongkun.hzk@bytedance.com> wrote:
> >
> > The MGLRU already supports reclaiming only from anonymous memory
> > via the /sys/kernel/debug/lru_gen interface. Now, memory.reclaim
> > also supports the swappiness=max parameter to enable reclaiming
> > solely from anonymous memory. To unify the semantics of proactive
> > reclaiming from anonymous folios, the max parameter is introduced.
> >
> > Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
>
> Acked-by: Muchun Song <muchun.song@linux.dev>
>

Thanks.

> Thanks.
>

[PATCH update] mm: add max swappiness arg to lru_gen for anonymous memory only

[Zhongkun He]

The MGLRU already supports reclaiming only from anonymous memory
via the /sys/kernel/debug/lru_gen interface. Now, memory.reclaim
also supports the swappiness=max parameter to enable reclaiming
solely from anonymous memory. To unify the semantics of proactive
reclaiming from anonymous folios, the max parameter is introduced.

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
update:
 1) use strcmp instead of strncmp from Dan Carpenter
https://lore.kernel.org/all/aBHYT27M1tRxNLRj@stanley.mountain/
 2) If swappiness is not set, use the default value.

 Documentation/admin-guide/mm/multigen_lru.rst |  5 +++--
 mm/vmscan.c                                   | 19 +++++++++++++++----
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/mm/multigen_lru.rst b/Documentation/admin-guide/mm/multigen_lru.rst
index 33e068830497..9cb54b4ff5d9 100644
--- a/Documentation/admin-guide/mm/multigen_lru.rst
+++ b/Documentation/admin-guide/mm/multigen_lru.rst
@@ -151,8 +151,9 @@ generations less than or equal to ``min_gen_nr``.
 ``min_gen_nr`` should be less than ``max_gen_nr-1``, since
 ``max_gen_nr`` and ``max_gen_nr-1`` are not fully aged (equivalent to
 the active list) and therefore cannot be evicted. ``swappiness``
-overrides the default value in ``/proc/sys/vm/swappiness``.
-``nr_to_reclaim`` limits the number of pages to evict.
+overrides the default value in ``/proc/sys/vm/swappiness`` and the valid
+range is [0-200, max], with max being exclusively used for the reclamation
+of anonymous memory. ``nr_to_reclaim`` limits the number of pages to evict.
 
 A typical use case is that a job scheduler runs this command before it
 tries to land a new job on a server. If it fails to materialize enough
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 49eb2a4e490d..31142acdcedc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5581,24 +5581,35 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
 	while ((cur = strsep(&next, ",;\n"))) {
 		int n;
 		int end;
-		char cmd;
+		char cmd, swap_string[5];
 		unsigned int memcg_id;
 		unsigned int nid;
 		unsigned long seq;
-		unsigned int swappiness = -1;
+		unsigned int swappiness;
 		unsigned long opt = -1;
 
 		cur = skip_spaces(cur);
 		if (!*cur)
 			continue;
 
-		n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
-			   &seq, &end, &swappiness, &end, &opt, &end);
+		n = sscanf(cur, "%c %u %u %lu %n %4s %n %lu %n", &cmd, &memcg_id, &nid,
+			   &seq, &end, swap_string, &end, &opt, &end);
 		if (n < 4 || cur[end]) {
 			err = -EINVAL;
 			break;
 		}
 
+		if (n == 4)
+			swappiness = -1;
+		else if (!strcmp("max", swap_string)) {
+			/* set by userspace for anonymous memory only */
+			swappiness = SWAPPINESS_ANON_ONLY;
+		} else {
+			err = kstrtouint(swap_string, 0, &swappiness);
+			if (err)
+				break;
+		}
+
 		err = run_cmd(cmd, memcg_id, nid, seq, &sc, swappiness, opt);
 		if (err)
 			break;
-- 
2.39.5