1 files changed, 102 insertions, 0 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 1cd15d6a9c49..05595d113ff8 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -20,6 +20,7 @@
 #include <linux/slab.h>
 #include <linux/sched/mm.h>
 #include <linux/log2.h>
+#include <linux/shrinker.h>
 #include <crypto/hash.h>
 #include "misc.h"
 #include "ctree.h"
@@ -170,15 +171,95 @@ static void btrfs_free_compressed_pages(struct compressed_bio *cb)
 static int btrfs_decompress_bio(struct compressed_bio *cb);
 
 /*
+ * Global cache of last unused pages for compression/decompression.
+ */
+static struct btrfs_compr_pool {
+	struct shrinker *shrinker;
+	spinlock_t lock;
+	struct list_head list;
+	int count;
+	int thresh;
+} compr_pool;
+
+static unsigned long btrfs_compr_pool_count(struct shrinker *sh, struct shrink_control *sc)
+{
+	int ret;
+
+	/*
+	 * We must not read the values more than once if 'ret' gets expanded in
+	 * the return statement so we don't accidentally return a negative
+	 * number, even if the first condition finds it positive.
+	 */
+	ret = READ_ONCE(compr_pool.count) - READ_ONCE(compr_pool.thresh);
+
+	return ret > 0 ? ret : 0;
+}
+
+static unsigned long btrfs_compr_pool_scan(struct shrinker *sh, struct shrink_control *sc)
+{
+	struct list_head remove;
+	struct list_head *tmp, *next;
+	int freed;
+
+	if (compr_pool.count == 0)
+		return SHRINK_STOP;
+
+	INIT_LIST_HEAD(&remove);
+
+	/* For now, just simply drain the whole list. */
+	spin_lock(&compr_pool.lock);
+	list_splice_init(&compr_pool.list, &remove);
+	freed = compr_pool.count;
+	compr_pool.count = 0;
+	spin_unlock(&compr_pool.lock);
+
+	list_for_each_safe(tmp, next, &remove) {
+		struct page *page = list_entry(tmp, struct page, lru);
+
+		ASSERT(page_ref_count(page) == 1);
+		put_page(page);
+	}
+
+	return freed;
+}
+
+/*
  * Common wrappers for page allocation from compression wrappers
  */
 struct page *btrfs_alloc_compr_page(void)
 {
+	struct page *page = NULL;
+
+	spin_lock(&compr_pool.lock);
+	if (compr_pool.count > 0) {
+		page = list_first_entry(&compr_pool.list, struct page, lru);
+		list_del_init(&page->lru);
+		compr_pool.count--;
+	}
+	spin_unlock(&compr_pool.lock);
+
+	if (page)
+		return page;
+
 	return alloc_page(GFP_NOFS);
 }
 
 void btrfs_free_compr_page(struct page *page)
 {
+	bool do_free = false;
+
+	spin_lock(&compr_pool.lock);
+	if (compr_pool.count > compr_pool.thresh) {
+		do_free = true;
+	} else {
+		list_add(&page->lru, &compr_pool.list);
+		compr_pool.count++;
+	}
+	spin_unlock(&compr_pool.lock);
+
+	if (!do_free)
+		return;
+
 	ASSERT(page_ref_count(page) == 1);
 	put_page(page);
 }
@@ -974,15 +1055,36 @@ int __init btrfs_init_compress(void)
 			offsetof(struct compressed_bio, bbio.bio),
 			BIOSET_NEED_BVECS))
 		return -ENOMEM;
+
+	compr_pool.shrinker = shrinker_alloc(SHRINKER_NONSLAB, "btrfs-compr-pages");
+	if (!compr_pool.shrinker)
+		return -ENOMEM;
+
 	btrfs_init_workspace_manager(BTRFS_COMPRESS_NONE);
 	btrfs_init_workspace_manager(BTRFS_COMPRESS_ZLIB);
 	btrfs_init_workspace_manager(BTRFS_COMPRESS_LZO);
 	zstd_init_workspace_manager();
+
+	spin_lock_init(&compr_pool.lock);
+	INIT_LIST_HEAD(&compr_pool.list);
+	compr_pool.count = 0;
+	/* 128K / 4K = 32, for 8 threads is 256 pages. */
+	compr_pool.thresh = BTRFS_MAX_COMPRESSED / PAGE_SIZE * 8;
+	compr_pool.shrinker->count_objects = btrfs_compr_pool_count;
+	compr_pool.shrinker->scan_objects = btrfs_compr_pool_scan;
+	compr_pool.shrinker->batch = 32;
+	compr_pool.shrinker->seeks = DEFAULT_SEEKS;
+	shrinker_register(compr_pool.shrinker);
+
 	return 0;
 }
 
 void __cold btrfs_exit_compress(void)
 {
+	/* For now scan drains all pages and does not touch the parameters. */
+	btrfs_compr_pool_scan(NULL, NULL);
+	shrinker_free(compr_pool.shrinker);
+
 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_NONE);
 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_ZLIB);
 	btrfs_cleanup_workspace_manager(BTRFS_COMPRESS_LZO);