f2fs: add a sysfs node to limit max read extent count per-inode

Quoted:
"at this time, there are still 1086911 extent nodes in this zombie
extent tree that need to be cleaned up.

crash_arm64_sprd_v8.0.3++> extent_tree.node_cnt ffffff80896cc500
  node_cnt = {
    counter = 1086911
  },
"

As reported by Xiuhong, there will be a huge number of extent nodes
in extent tree, it may potentially cause:
- slab memory fragments
- extreme long time shrink on extent tree
- low mapping efficiency

Let's add a sysfs node to limit max read extent count for each inode,
by default, value of this threshold is 10240, it can be updated
according to user's requirement.

Reported-by: Xiuhong Wang <xiuhong.wang@unisoc.com>
Closes: https://lore.kernel.org/linux-f2fs-devel/20241112110627.1314632-1-xiuhong.wang@unisoc.com/
Signed-off-by: Xiuhong Wang <xiuhong.wang@unisoc.com>
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index b65b023a588a..6f2cbf4c5740 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -635,6 +635,9 @@ enum {
 #define DEF_HOT_DATA_AGE_THRESHOLD	262144
 #define DEF_WARM_DATA_AGE_THRESHOLD	2621440
 
+/* default max read extent count per inode */
+#define DEF_MAX_READ_EXTENT_COUNT	10240
+
 /* extent cache type */
 enum extent_type {
 	EX_READ,
@@ -1619,6 +1622,7 @@ struct f2fs_sb_info {
 	/* for extent tree cache */
 	struct extent_tree_info extent_tree[NR_EXTENT_CACHES];
 	atomic64_t allocated_data_blocks;	/* for block age extent_cache */
+	unsigned int max_read_extent_count;	/* max read extent count per inode */
 
 	/* The threshold used for hot and warm data seperation*/
 	unsigned int hot_data_age_threshold;