[RFC PATCH 1/3] mm/memcontrol: Introduce per-cgroup compression priority

On Android, applications have varying tolerance for decompression speed.
Background and lightweight applications tolerate slower decompression
better than large, foreground applications. They are suitable for
algorithms like ZSTD, which has a high compression ratio but slower
decompression. Other applications may prefer algorithms with faster
decompression.

This patch introduces a per-cgroup compression priority mechanism.
Different compression priorities map to different algorithms. This
allows administrators to select the appropriate compression algorithm
on a per-cgroup basis.
---
 include/linux/memcontrol.h | 19 +++++++++++++++++++
 mm/memcontrol.c            | 31 +++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 873e510d6f8d..a91670b8c469 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -228,6 +228,9 @@ struct mem_cgroup {
 
 	int swappiness;
 
+	/* The priority of the compression algorithm used by the cgroup. */
+	int comp_priority;
+
 	/* memory.events and memory.events.local */
 	struct cgroup_file events_file;
 	struct cgroup_file events_local_file;
@@ -523,6 +526,22 @@ static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *ob
 	return memcg;
 }
 
+#define DEF_COMP_PRIORITY 0
+
+/*
+* get_cgroup_comp_priority - Get the compression priority of the memcg
+* @page: Pointer to the page.
+* Returns the compression priority of the memcg the page belongs to.
+*/
+static inline int get_cgroup_comp_priority(struct page *page)
+{
+	struct mem_cgroup *memcg = folio_memcg(page_folio(page));
+	if (!memcg)
+		return DEF_COMP_PRIORITY;
+
+	return memcg->comp_priority;
+}
+
 /*
  * folio_memcg_kmem - Check if the folio has the memcg_kmem flag set.
  * @folio: Pointer to the folio.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4deda33625f4..436cbc8ddcc2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5356,6 +5356,31 @@ static int swap_events_show(struct seq_file *m, void *v)
 	return 0;
 }
 
+static int swap_comp_priority_show(struct seq_file *m, void *v)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+
+	seq_printf(m, "%d\n", READ_ONCE(memcg->comp_priority));
+	return 0;
+}
+
+static ssize_t swap_comp_priority_write(struct kernfs_open_file *of,
+					  char *buf, size_t nbytes, loff_t off)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+	int comp_priority;
+	ssize_t parse_ret = kstrtoint(strstrip(buf), 10, &comp_priority);
+
+	if (parse_ret)
+		return parse_ret;
+
+	if (comp_priority < 0)
+		return -EINVAL;
+
+	WRITE_ONCE(memcg->comp_priority, comp_priority);
+	return nbytes;
+}
+
 static struct cftype swap_files[] = {
 	{
 		.name = "swap.current",
@@ -5388,6 +5413,12 @@ static struct cftype swap_files[] = {
 		.file_offset = offsetof(struct mem_cgroup, swap_events_file),
 		.seq_show = swap_events_show,
 	},
+	{
+		.name = "swap.comp_priority",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = swap_comp_priority_show,
+		.write = swap_comp_priority_write,
+	},
 	{ }	/* terminate */
 };
 
-- 
2.48.1