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

[Zhongkun He <hezhongkun.hzk@bytedance.com>]

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