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>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -822,3 +822,9 @@ Description:	It controls the valid block ratio threshold not to trigger excessiv
 		for zoned deivces. The initial value of it is 95(%). F2FS will stop the
 		background GC thread from intiating GC for sections having valid blocks
 		exceeding the ratio.
+
+What:		/sys/fs/f2fs/<disk>/max_read_extent_count
+Date:		November 2024
+Contact:	"Chao Yu" <chao@kernel.org>
+Description:	It controls max read extent count for per-inode, the value of threshold
+		is 10240 by default.

fs/f2fs/extent_cache.c

@@ -717,7 +717,9 @@ static void __update_extent_tree_range(struct inode *inode,
 		}
 
 		if (end < org_end && (type != EX_READ ||
-				org_end - end >= F2FS_MIN_EXTENT_LEN)) {
+			(org_end - end >= F2FS_MIN_EXTENT_LEN &&
+			atomic_read(&et->node_cnt) <
+					sbi->max_read_extent_count))) {
 			if (parts) {
 				__set_extent_info(&ei,
 					end, org_end - end,
@@ -1212,6 +1214,7 @@ void f2fs_init_extent_cache_info(struct f2fs_sb_info *sbi)
 	sbi->hot_data_age_threshold = DEF_HOT_DATA_AGE_THRESHOLD;
 	sbi->warm_data_age_threshold = DEF_WARM_DATA_AGE_THRESHOLD;
 	sbi->last_age_weight = LAST_AGE_WEIGHT;
+	sbi->max_read_extent_count = DEF_MAX_READ_EXTENT_COUNT;
 }
 
 int __init f2fs_create_extent_cache(void)

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;

fs/f2fs/sysfs.c

@@ -787,6 +787,13 @@ out:
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "max_read_extent_count")) {
+		if (t > UINT_MAX)
+			return -EINVAL;
+		*ui = (unsigned int)t;
+		return count;
+	}
+
 	if (!strcmp(a->attr.name, "ipu_policy")) {
 		if (t >= BIT(F2FS_IPU_MAX))
 			return -EINVAL;
@@ -1052,6 +1059,8 @@ F2FS_SBI_GENERAL_RW_ATTR(revoked_atomic_block);
 F2FS_SBI_GENERAL_RW_ATTR(hot_data_age_threshold);
 F2FS_SBI_GENERAL_RW_ATTR(warm_data_age_threshold);
 F2FS_SBI_GENERAL_RW_ATTR(last_age_weight);
+/* read extent cache */
+F2FS_SBI_GENERAL_RW_ATTR(max_read_extent_count);
 #ifdef CONFIG_BLK_DEV_ZONED
 F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
 F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
@@ -1242,6 +1251,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(hot_data_age_threshold),
 	ATTR_LIST(warm_data_age_threshold),
 	ATTR_LIST(last_age_weight),
+	ATTR_LIST(max_read_extent_count),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);