From 1a9d73b5c0b949fd4b53935a43e7dc1e0d9d1127 Mon Sep 17 00:00:00 2001
From: Kent Overstreet <kent.overstreet@gmail.com>
Date: Mon, 21 Mar 2022 20:20:09 -0400
Subject: [PATCH] Shrinker improvements

After memory allocation failure, don't rely on /proc/meminfo to figure
out how much memory we should free - instead unconditionally free 1/8th
of each cache.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
 include/linux/shrinker.h |  2 +-
 include/linux/slab.h     |  4 ++--
 include/linux/vmalloc.h  |  2 +-
 linux/shrinker.c         | 27 +++++++++++++++++++++++++--
 4 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 626b768c..eba6cfdd 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -25,6 +25,6 @@ struct shrinker {
 int register_shrinker(struct shrinker *);
 void unregister_shrinker(struct shrinker *);
 
-void run_shrinkers(void);
+void run_shrinkers(gfp_t gfp_mask, bool);
 
 #endif /* __TOOLS_LINUX_SHRINKER_H */
diff --git a/include/linux/slab.h b/include/linux/slab.h
index bc99973f..557c0411 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -20,7 +20,7 @@ static inline void *kmalloc(size_t size, gfp_t flags)
 	void *p;
 
 	do {
-		run_shrinkers();
+		run_shrinkers(flags, i != 0);
 
 		if (size) {
 			size_t alignment = min(rounddown_pow_of_two(size), (size_t)PAGE_SIZE);
@@ -83,7 +83,7 @@ static inline struct page *alloc_pages(gfp_t flags, unsigned int order)
 	void *p;
 
 	do {
-		run_shrinkers();
+		run_shrinkers(flags, i != 0);
 
 		p = aligned_alloc(PAGE_SIZE, size);
 		if (p && (flags & __GFP_ZERO))
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index ccb319eb..965e341d 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -20,7 +20,7 @@ static inline void *__vmalloc(unsigned long size, gfp_t gfp_mask)
 	size = round_up(size, PAGE_SIZE);
 
 	do {
-		run_shrinkers();
+		run_shrinkers(gfp_mask, i != 0);
 
 		p = aligned_alloc(PAGE_SIZE, size);
 		if (p && gfp_mask & __GFP_ZERO)
diff --git a/linux/shrinker.c b/linux/shrinker.c
index f6c979aa..876c1bae 100644
--- a/linux/shrinker.c
+++ b/linux/shrinker.c
@@ -65,7 +65,24 @@ static struct meminfo read_meminfo(void)
 	return ret;
 }
 
-void run_shrinkers(void)
+static void run_shrinkers_allocation_failed(gfp_t gfp_mask)
+{
+	struct shrinker *shrinker;
+
+	mutex_lock(&shrinker_lock);
+	list_for_each_entry(shrinker, &shrinker_list, list) {
+		struct shrink_control sc = { .gfp_mask	= gfp_mask, };
+
+		unsigned long have = shrinker->count_objects(shrinker, &sc);
+
+		sc.nr_to_scan = have / 8;
+
+		shrinker->scan_objects(shrinker, &sc);
+	}
+	mutex_unlock(&shrinker_lock);
+}
+
+void run_shrinkers(gfp_t gfp_mask, bool allocation_failed)
 {
 	struct shrinker *shrinker;
 	struct meminfo info;
@@ -75,6 +92,11 @@ void run_shrinkers(void)
 	if (list_empty(&shrinker_list))
 		return;
 
+	if (allocation_failed) {
+		run_shrinkers_allocation_failed(gfp_mask);
+		return;
+	}
+
 	info = read_meminfo();
 
 	if (info.total && info.available) {
@@ -92,7 +114,8 @@ void run_shrinkers(void)
 	mutex_lock(&shrinker_lock);
 	list_for_each_entry(shrinker, &shrinker_list, list) {
 		struct shrink_control sc = {
-			.nr_to_scan = want_shrink >> PAGE_SHIFT
+			.gfp_mask	= gfp_mask,
+			.nr_to_scan	= want_shrink >> PAGE_SHIFT
 		};
 
 		shrinker->scan_objects(shrinker, &sc);