mm/memcg: make memory.reclaim interface generic

This adds a general call for both parsing as well as the common reclaim
semantics.  memcg is still the only user and no change in semantics.

[akpm@linux-foundation.org: fix CONFIG_NUMA=n build]
Link: https://lkml.kernel.org/r/20250623185851.830632-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/internal.h

@@ -533,6 +533,16 @@ extern unsigned long highest_memmap_pfn;
 bool folio_isolate_lru(struct folio *folio);
 void folio_putback_lru(struct folio *folio);
 extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
+#ifdef CONFIG_NUMA
+int user_proactive_reclaim(char *buf,
+			   struct mem_cgroup *memcg, pg_data_t *pgdat);
+#else
+static inline int user_proactive_reclaim(char *buf,
+			   struct mem_cgroup *memcg, pg_data_t *pgdat)
+{
+	return 0;
+}
+#endif
 
 /*
  * in mm/rmap.c:

mm/memcontrol.c

@@ -51,7 +51,6 @@
 #include <linux/spinlock.h>
 #include <linux/fs.h>
 #include <linux/seq_file.h>
-#include <linux/parser.h>
 #include <linux/vmpressure.h>
 #include <linux/memremap.h>
 #include <linux/mm_inline.h>
@@ -4564,83 +4563,15 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
 	return nbytes;
 }
 
-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 },
-};
-
 static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
 			      size_t nbytes, loff_t off)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
-	unsigned int nr_retries = MAX_RECLAIM_RETRIES;
+	int ret;
-	unsigned long nr_to_reclaim, nr_reclaimed = 0;
-	int swappiness = -1;
-	unsigned int reclaim_options;
-	char *old_buf, *start;
-	substring_t args[MAX_OPT_ARGS];
 
-	buf = strstrip(buf);
+	ret = user_proactive_reclaim(buf, memcg, NULL);
-
+	if (ret)
-	old_buf = buf;
+		return ret;
-	nr_to_reclaim = memparse(buf, &buf) / PAGE_SIZE;
-	if (buf == old_buf)
-		return -EINVAL;
-
-	buf = strstrip(buf);
-
-	while ((start = strsep(&buf, " ")) != NULL) {
-		if (!strlen(start))
-			continue;
-		switch (match_token(start, tokens, args)) {
-		case MEMORY_RECLAIM_SWAPPINESS:
-			if (match_int(&args[0], &swappiness))
-				return -EINVAL;
-			if (swappiness < MIN_SWAPPINESS || swappiness > MAX_SWAPPINESS)
-				return -EINVAL;
-			break;
-		case MEMORY_RECLAIM_SWAPPINESS_MAX:
-			swappiness = SWAPPINESS_ANON_ONLY;
-			break;
-		default:
-			return -EINVAL;
-		}
-	}
-
-	reclaim_options	= MEMCG_RECLAIM_MAY_SWAP | MEMCG_RECLAIM_PROACTIVE;
-	while (nr_reclaimed < nr_to_reclaim) {
-		/* Will converge on zero, but reclaim enforces a minimum */
-		unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
-		unsigned long reclaimed;
-
-		if (signal_pending(current))
-			return -EINTR;
-
-		/*
-		 * This is the final attempt, drain percpu lru caches in the
-		 * hope of introducing more evictable pages for
-		 * try_to_free_mem_cgroup_pages().
-		 */
-		if (!nr_retries)
-			lru_add_drain_all();
-
-		reclaimed = try_to_free_mem_cgroup_pages(memcg,
-					batch_size, GFP_KERNEL,
-					reclaim_options,
-					swappiness == -1 ? NULL : &swappiness);
-
-		if (!reclaimed && !nr_retries--)
-			return -EAGAIN;
-
-		nr_reclaimed += reclaimed;
-	}
 
 	return nbytes;
 }

mm/vmscan.c

@@ -57,6 +57,7 @@
 #include <linux/rculist_nulls.h>
 #include <linux/random.h>
 #include <linux/mmu_notifier.h>
+#include <linux/parser.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -6714,6 +6715,15 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 
 	return nr_reclaimed;
 }
+#else
+unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
+					   unsigned long nr_pages,
+					   gfp_t gfp_mask,
+					   unsigned int reclaim_options,
+					   int *swappiness)
+{
+	return 0;
+}
 #endif
 
 static void kswapd_age_node(struct pglist_data *pgdat, struct scan_control *sc)
@@ -7708,6 +7718,94 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 
 	return ret;
 }
+
+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 },
+};
+
+int user_proactive_reclaim(char *buf, struct mem_cgroup *memcg, pg_data_t *pgdat)
+{
+	unsigned int nr_retries = MAX_RECLAIM_RETRIES;
+	unsigned long nr_to_reclaim, nr_reclaimed = 0;
+	int swappiness = -1;
+	char *old_buf, *start;
+	substring_t args[MAX_OPT_ARGS];
+
+	if (!buf || (!memcg && !pgdat))
+		return -EINVAL;
+
+	buf = strstrip(buf);
+
+	old_buf = buf;
+	nr_to_reclaim = memparse(buf, &buf) / PAGE_SIZE;
+	if (buf == old_buf)
+		return -EINVAL;
+
+	buf = strstrip(buf);
+
+	while ((start = strsep(&buf, " ")) != NULL) {
+		if (!strlen(start))
+			continue;
+		switch (match_token(start, tokens, args)) {
+		case MEMORY_RECLAIM_SWAPPINESS:
+			if (match_int(&args[0], &swappiness))
+				return -EINVAL;
+			if (swappiness < MIN_SWAPPINESS ||
+			    swappiness > MAX_SWAPPINESS)
+				return -EINVAL;
+			break;
+		case MEMORY_RECLAIM_SWAPPINESS_MAX:
+			swappiness = SWAPPINESS_ANON_ONLY;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	while (nr_reclaimed < nr_to_reclaim) {
+		/* Will converge on zero, but reclaim enforces a minimum */
+		unsigned long batch_size = (nr_to_reclaim - nr_reclaimed) / 4;
+		unsigned long reclaimed;
+
+		if (signal_pending(current))
+			return -EINTR;
+
+		/*
+		 * This is the final attempt, drain percpu lru caches in the
+		 * hope of introducing more evictable pages.
+		 */
+		if (!nr_retries)
+			lru_add_drain_all();
+
+		if (memcg) {
+			unsigned int reclaim_options;
+
+			reclaim_options = MEMCG_RECLAIM_MAY_SWAP |
+					  MEMCG_RECLAIM_PROACTIVE;
+			reclaimed = try_to_free_mem_cgroup_pages(memcg,
+						 batch_size, GFP_KERNEL,
+						 reclaim_options,
+						 swappiness == -1 ? NULL : &swappiness);
+		} else {
+			return -EINVAL;
+		}
+
+		if (!reclaimed && !nr_retries--)
+			return -EAGAIN;
+
+		nr_reclaimed += reclaimed;
+	}
+
+	return 0;
+}
+
 #endif
 
 /**