erofs: add sysfs node to drop internal caches

Add a sysfs node to drop compression-related caches, currently used to
drop in-memory pclusters and cached compressed folios.

Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241113041148.749129-1-guochunhai@vivo.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: Chunhai Guo

Documentation/ABI/testing/sysfs-fs-erofs

@@ -16,3 +16,14 @@ Description:	Control strategy of sync decompression:
 		  readahead on atomic contexts only.
 		- 1 (force on): enable for readpage and readahead.
 		- 2 (force off): disable for all situations.
+
+What:		/sys/fs/erofs/<disk>/drop_caches
+Date:		November 2024
+Contact:	"Guo Chunhai" <guochunhai@vivo.com>
+Description:	Writing to this will drop compression-related caches,
+		currently used to drop in-memory pclusters and cached
+		compressed folios:
+
+		- 1 : invalidate cached compressed folios
+		- 2 : drop in-memory pclusters
+		- 3 : drop in-memory pclusters and cached compressed folios

fs/erofs/internal.h

@@ -450,6 +450,8 @@ static inline void erofs_pagepool_add(struct page **pagepool, struct page *page)
 void erofs_release_pages(struct page **pagepool);
 
 #ifdef CONFIG_EROFS_FS_ZIP
+#define MNGD_MAPPING(sbi)	((sbi)->managed_cache->i_mapping)
+
 extern atomic_long_t erofs_global_shrink_cnt;
 void erofs_shrinker_register(struct super_block *sb);
 void erofs_shrinker_unregister(struct super_block *sb);

fs/erofs/sysfs.c

@@ -10,6 +10,7 @@
 
 enum {
 	attr_feature,
+	attr_drop_caches,
 	attr_pointer_ui,
 	attr_pointer_bool,
 };
@@ -57,11 +58,13 @@ static struct erofs_attr erofs_attr_##_name = {			\
 
 #ifdef CONFIG_EROFS_FS_ZIP
 EROFS_ATTR_RW_UI(sync_decompress, erofs_mount_opts);
+EROFS_ATTR_FUNC(drop_caches, 0200);
 #endif
 
 static struct attribute *erofs_attrs[] = {
 #ifdef CONFIG_EROFS_FS_ZIP
 	ATTR_LIST(sync_decompress),
+	ATTR_LIST(drop_caches),
 #endif
 	NULL,
 };
@@ -163,6 +166,20 @@ static ssize_t erofs_attr_store(struct kobject *kobj, struct attribute *attr,
 			return -EINVAL;
 		*(bool *)ptr = !!t;
 		return len;
+#ifdef CONFIG_EROFS_FS_ZIP
+	case attr_drop_caches:
+		ret = kstrtoul(skip_spaces(buf), 0, &t);
+		if (ret)
+			return ret;
+		if (t < 1 || t > 3)
+			return -EINVAL;
+
+		if (t & 2)
+			z_erofs_shrink_scan(sbi, ~0UL);
+		if (t & 1)
+			invalidate_mapping_pages(MNGD_MAPPING(sbi), 0, -1);
+		return len;
+#endif
 	}
 	return 0;
 }

fs/erofs/zdata.c

@@ -119,7 +119,6 @@ static inline unsigned int z_erofs_pclusterpages(struct z_erofs_pcluster *pcl)
 	return PAGE_ALIGN(pcl->pclustersize) >> PAGE_SHIFT;
 }
 
-#define MNGD_MAPPING(sbi)	((sbi)->managed_cache->i_mapping)
 static bool erofs_folio_is_managed(struct erofs_sb_info *sbi, struct folio *fo)
 {
 	return fo->mapping == MNGD_MAPPING(sbi);