The current ocfs2 code can't reclaim suballocator block group space.
This cause ocfs2 to hold onto a lot of space in some cases. for example,
when creating lots of small files, the space is held/managed by
'//inode_alloc'. After the user deletes all the small files, the space
never returns to '//global_bitmap'. This issue prevents ocfs2 from
providing the needed space even when there is enough free space in a
small ocfs2 volume.
This patch gives ocfs2 the ability to reclaim suballoc free space when
the block group is freed. For performance reasons, this patch keeps
the first suballocator block group.

Signed-off-by: Heming Zhao <heming.zhao@suse.com>
Reviewed-by: Su Yue <glass.su@suse.com>
---
 fs/ocfs2/suballoc.c | 302 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 292 insertions(+), 10 deletions(-)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index f7b483f0de2a..d62010166c34 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -294,6 +294,68 @@ static int ocfs2_validate_group_descriptor(struct super_block *sb,
 	return ocfs2_validate_gd_self(sb, bh, 0);
 }
 
+/*
+ * hint gd may already be released in _ocfs2_free_suballoc_bits(),
+ * we first check gd descriptor signature, then do the
+ * ocfs2_read_group_descriptor() jobs.
+ *
+ * When the group descriptor is invalid, we return 'rc=0' and
+ * '*released=1'. The caller should handle this case. Otherwise,
+ * we return the real error code.
+ */
+static int ocfs2_read_hint_group_descriptor(struct inode *inode,
+			struct ocfs2_dinode *di, u64 gd_blkno,
+			struct buffer_head **bh, int *released)
+{
+	int rc;
+	struct buffer_head *tmp = *bh;
+	struct ocfs2_group_desc *gd;
+
+	*released = 0;
+
+	rc = ocfs2_read_block(INODE_CACHE(inode), gd_blkno, &tmp, NULL);
+	if (rc)
+		goto out;
+
+	gd = (struct ocfs2_group_desc *) tmp->b_data;
+	if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
+		/*
+		 * Invalid gd cache was set in ocfs2_read_block(),
+		 * which will affect block_group allocation.
+		 * Path:
+		 * ocfs2_reserve_suballoc_bits
+		 *  ocfs2_block_group_alloc
+		 *   ocfs2_block_group_alloc_contig
+		 *    ocfs2_set_new_buffer_uptodate
+		 */
+		ocfs2_remove_from_cache(INODE_CACHE(inode), tmp);
+		*released = 1; /* we return 'rc=0' for this case */
+		goto free_bh;
+	}
+
+	/* below jobs same with ocfs2_read_group_descriptor() */
+	if (!buffer_jbd(tmp)) {
+		rc = ocfs2_validate_group_descriptor(inode->i_sb, tmp);
+		if (rc)
+			goto free_bh;
+	}
+
+	rc = ocfs2_validate_gd_parent(inode->i_sb, di, tmp, 0);
+	if (rc)
+		goto free_bh;
+
+	/* If ocfs2_read_block() got us a new bh, pass it up. */
+	if (!*bh)
+		*bh = tmp;
+
+	return rc;
+
+free_bh:
+	brelse(tmp);
+out:
+	return rc;
+}
+
 int ocfs2_read_group_descriptor(struct inode *inode, struct ocfs2_dinode *di,
 				u64 gd_blkno, struct buffer_head **bh)
 {
@@ -1722,7 +1784,7 @@ static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
 				  u32 bits_wanted,
 				  u32 min_bits,
 				  struct ocfs2_suballoc_result *res,
-				  u16 *bits_left)
+				  u16 *bits_left, int *released)
 {
 	int ret;
 	struct buffer_head *group_bh = NULL;
@@ -1730,9 +1792,11 @@ static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
 	struct ocfs2_dinode *di = (struct ocfs2_dinode *)ac->ac_bh->b_data;
 	struct inode *alloc_inode = ac->ac_inode;
 
-	ret = ocfs2_read_group_descriptor(alloc_inode, di,
-					  res->sr_bg_blkno, &group_bh);
-	if (ret < 0) {
+	ret = ocfs2_read_hint_group_descriptor(alloc_inode, di,
+				res->sr_bg_blkno, &group_bh, released);
+	if (*released) {
+		return 0;
+	} else if (ret < 0) {
 		mlog_errno(ret);
 		return ret;
 	}
@@ -1934,7 +1998,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
 				     u32 min_bits,
 				     struct ocfs2_suballoc_result *res)
 {
-	int status;
+	int status, released;
 	u16 victim, i;
 	u16 bits_left = 0;
 	u64 hint = ac->ac_last_group;
@@ -1961,6 +2025,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
 		goto bail;
 	}
 
+	/* the hint bg may already be released, we quiet search this group. */
 	res->sr_bg_blkno = hint;
 	if (res->sr_bg_blkno) {
 		/* Attempt to short-circuit the usual search mechanism
@@ -1968,7 +2033,12 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
 		 * allocation group. This helps us maintain some
 		 * contiguousness across allocations. */
 		status = ocfs2_search_one_group(ac, handle, bits_wanted,
-						min_bits, res, &bits_left);
+						min_bits, res, &bits_left,
+						&released);
+		if (released) {
+			res->sr_bg_blkno = 0;
+			goto chain_search;
+		}
 		if (!status)
 			goto set_hint;
 		if (status < 0 && status != -ENOSPC) {
@@ -1976,7 +2046,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
 			goto bail;
 		}
 	}
-
+chain_search:
 	cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;
 
 	victim = ocfs2_find_victim_chain(cl);
@@ -2077,6 +2147,12 @@ int ocfs2_claim_metadata(handle_t *handle,
 	return status;
 }
 
+/*
+ * after ocfs2 has the ability to release block group unused space,
+ * the ->ip_last_used_group may be invalid. so this function returns
+ * ac->ac_last_group need to verify.
+ * refer the 'hint' in ocfs2_claim_suballoc_bits() for more details.
+ */
 static void ocfs2_init_inode_ac_group(struct inode *dir,
 				      struct buffer_head *parent_di_bh,
 				      struct ocfs2_alloc_context *ac)
@@ -2514,6 +2590,197 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
 	return status;
 }
 
+/*
+ * Reclaim the suballocator managed space to main bitmap.
+ * This function first works on the suballocator then switch to the
+ * main bitmap.
+ *
+ * handle: The transaction handle
+ * alloc_inode: The suballoc inode
+ * alloc_bh: The buffer_head of suballoc inode
+ * group_bh: The group descriptor buffer_head of suballocator managed.
+ *           Caller should release the input group_bh.
+ */
+static int _reclaim_to_main_bm(handle_t *handle,
+			struct inode *alloc_inode,
+			struct buffer_head *alloc_bh,
+			struct buffer_head *group_bh)
+{
+	int idx, status = 0;
+	int i, next_free_rec, len = 0;
+	__le16 old_bg_contig_free_bits = 0;
+	u16 start_bit;
+	u32 tmp_used;
+	u64 bg_blkno, start_blk;
+	unsigned int count;
+	struct ocfs2_chain_rec *rec;
+	struct buffer_head *main_bm_bh = NULL;
+	struct inode *main_bm_inode = NULL;
+	struct ocfs2_super *osb = OCFS2_SB(alloc_inode->i_sb);
+	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) alloc_bh->b_data;
+	struct ocfs2_chain_list *cl = &fe->id2.i_chain;
+	struct ocfs2_group_desc *group = (struct ocfs2_group_desc *) group_bh->b_data;
+
+	idx = le16_to_cpu(group->bg_chain);
+	rec = &(cl->cl_recs[idx]);
+
+	status = ocfs2_extend_trans(handle,
+				ocfs2_calc_group_alloc_credits(osb->sb,
+						 le16_to_cpu(cl->cl_cpg)));
+	if (status) {
+		mlog_errno(status);
+		goto bail;
+	}
+	status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
+					 alloc_bh, OCFS2_JOURNAL_ACCESS_WRITE);
+	if (status < 0) {
+		mlog_errno(status);
+		goto bail;
+	}
+
+	/*
+	 * Only clear the suballocator rec item in-place.
+	 *
+	 * If idx is not the last, we don't compress (remove the empty item)
+	 * the cl_recs[]. If not, we need to do lots jobs.
+	 *
+	 * Compress cl_recs[] code example:
+	 * if (idx != cl->cl_next_free_rec - 1)
+	 * 	memmove(&cl->cl_recs[idx], &cl->cl_recs[idx + 1],
+	 * 		sizeof(struct ocfs2_chain_rec) *
+	 * 		(cl->cl_next_free_rec - idx - 1));
+	 * for(i = idx; i < cl->cl_next_free_rec-1; i++) {
+	 * 	group->bg_chain = "later group->bg_chain";
+	 * 	group->bg_blkno = xxx;
+	 * 	... ...
+	 * }
+	 */
+
+	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_total);
+	fe->id1.bitmap1.i_total = cpu_to_le32(tmp_used - le32_to_cpu(rec->c_total));
+
+	/* Substraction 1 for the block group itself */
+	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
+	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - 1);
+
+	tmp_used = le32_to_cpu(fe->i_clusters);
+	fe->i_clusters = cpu_to_le32(tmp_used - le16_to_cpu(cl->cl_cpg));
+
+	spin_lock(&OCFS2_I(alloc_inode)->ip_lock);
+	OCFS2_I(alloc_inode)->ip_clusters -= le32_to_cpu(fe->i_clusters);
+	fe->i_size = cpu_to_le64(ocfs2_clusters_to_bytes(alloc_inode->i_sb,
+					     le32_to_cpu(fe->i_clusters)));
+	spin_unlock(&OCFS2_I(alloc_inode)->ip_lock);
+	i_size_write(alloc_inode, le64_to_cpu(fe->i_size));
+	alloc_inode->i_blocks = ocfs2_inode_sector_count(alloc_inode);
+
+	ocfs2_journal_dirty(handle, alloc_bh);
+	ocfs2_update_inode_fsync_trans(handle, alloc_inode, 0);
+
+	start_blk = le64_to_cpu(rec->c_blkno);
+	count = le32_to_cpu(rec->c_total) / le16_to_cpu(cl->cl_bpc);
+
+	/*
+	 * If the rec is the last one, let's compress the chain list by
+	 * removing the empty cl_recs[] at the end.
+	 */
+	next_free_rec = le16_to_cpu(cl->cl_next_free_rec);
+	if (idx == (next_free_rec - 1)) {
+		len++; /* the last item should be counted first */
+		for (i = (next_free_rec - 2); i > 0; i--) {
+			if (cl->cl_recs[i].c_free == cl->cl_recs[i].c_total)
+				len++;
+			else
+				break;
+		}
+	}
+	le16_add_cpu(&cl->cl_next_free_rec, -len);
+
+	rec->c_free = 0;
+	rec->c_total = 0;
+	rec->c_blkno = 0;
+	ocfs2_remove_from_cache(INODE_CACHE(alloc_inode), group_bh);
+	memset(group, 0, sizeof(struct ocfs2_group_desc));
+
+	/* prepare job for reclaim clusters */
+	main_bm_inode = ocfs2_get_system_file_inode(osb,
+						    GLOBAL_BITMAP_SYSTEM_INODE,
+						    OCFS2_INVALID_SLOT);
+	if (!main_bm_inode)
+		goto bail; /* ignore the error in reclaim path */
+
+	inode_lock(main_bm_inode);
+
+	status = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 1);
+	if (status < 0)
+		goto free_bm_inode; /* ignore the error in reclaim path */
+
+	ocfs2_block_to_cluster_group(main_bm_inode, start_blk, &bg_blkno,
+				     &start_bit);
+	fe = (struct ocfs2_dinode *) main_bm_bh->b_data;
+	cl = &fe->id2.i_chain;
+	/* reuse group_bh, caller will release the input group_bh */
+	group_bh = NULL;
+
+	/* reclaim clusters to global_bitmap */
+	status = ocfs2_read_group_descriptor(main_bm_inode, fe, bg_blkno,
+					     &group_bh);
+	if (status < 0) {
+		mlog_errno(status);
+		goto free_bm_bh;
+	}
+	group = (struct ocfs2_group_desc *) group_bh->b_data;
+
+	if ((count + start_bit) > le16_to_cpu(group->bg_bits)) {
+		ocfs2_error(alloc_inode->i_sb,
+			"reclaim length (%d) beyands block group length (%d)",
+			count + start_bit, le16_to_cpu(group->bg_bits));
+		goto free_group_bh;
+	}
+
+	old_bg_contig_free_bits = group->bg_contig_free_bits;
+	status = ocfs2_block_group_clear_bits(handle, main_bm_inode,
+					      group, group_bh,
+					      start_bit, count, 0,
+					      _ocfs2_clear_bit);
+	if (status < 0) {
+		mlog_errno(status);
+		goto free_group_bh;
+	}
+
+	status = ocfs2_journal_access_di(handle, INODE_CACHE(main_bm_inode),
+					 main_bm_bh, OCFS2_JOURNAL_ACCESS_WRITE);
+	if (status < 0) {
+		mlog_errno(status);
+		ocfs2_block_group_set_bits(handle, main_bm_inode, group, group_bh,
+				start_bit, count,
+				le16_to_cpu(old_bg_contig_free_bits), 1);
+		goto free_group_bh;
+	}
+
+	idx = le16_to_cpu(group->bg_chain);
+	rec = &(cl->cl_recs[idx]);
+
+	le32_add_cpu(&rec->c_free, count);
+	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
+	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
+	ocfs2_journal_dirty(handle, main_bm_bh);
+
+free_group_bh:
+	brelse(group_bh);
+
+free_bm_bh:
+	ocfs2_inode_unlock(main_bm_inode, 1);
+	brelse(main_bm_bh);
+
+free_bm_inode:
+	inode_unlock(main_bm_inode);
+	iput(main_bm_inode);
+
+bail:
+	return status;
+}
+
 /*
  * expects the suballoc inode to already be locked.
  */
@@ -2526,12 +2793,13 @@ static int _ocfs2_free_suballoc_bits(handle_t *handle,
 				     void (*undo_fn)(unsigned int bit,
 						     unsigned long *bitmap))
 {
-	int status = 0;
+	int idx, status = 0;
 	u32 tmp_used;
 	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) alloc_bh->b_data;
 	struct ocfs2_chain_list *cl = &fe->id2.i_chain;
 	struct buffer_head *group_bh = NULL;
 	struct ocfs2_group_desc *group;
+	struct ocfs2_chain_rec *rec;
 	__le16 old_bg_contig_free_bits = 0;
 
 	/* The alloc_bh comes from ocfs2_free_dinode() or
@@ -2577,12 +2845,26 @@ static int _ocfs2_free_suballoc_bits(handle_t *handle,
 		goto bail;
 	}
 
-	le32_add_cpu(&cl->cl_recs[le16_to_cpu(group->bg_chain)].c_free,
-		     count);
+	idx = le16_to_cpu(group->bg_chain);
+	rec = &(cl->cl_recs[idx]);
+
+	le32_add_cpu(&rec->c_free, count);
 	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
 	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
 	ocfs2_journal_dirty(handle, alloc_bh);
 
+	/*
+	 * Reclaim suballocator free space.
+	 * Bypass: global_bitmap, not empty rec, first rec in cl_recs[]
+	 */
+	if (ocfs2_is_cluster_bitmap(alloc_inode) ||
+	    (le32_to_cpu(rec->c_free) != (le32_to_cpu(rec->c_total) - 1)) ||
+	    (le16_to_cpu(cl->cl_next_free_rec) == 1)) {
+		goto bail;
+	}
+
+	_reclaim_to_main_bm(handle, alloc_inode, alloc_bh, group_bh);
+
 bail:
 	brelse(group_bh);
 	return status;
-- 
2.35.3

On 9/8/24 10:07 PM, Heming Zhao wrote:
> The current ocfs2 code can't reclaim suballocator block group space.
> This cause ocfs2 to hold onto a lot of space in some cases. for example,
> when creating lots of small files, the space is held/managed by
> '//inode_alloc'. After the user deletes all the small files, the space
> never returns to '//global_bitmap'. This issue prevents ocfs2 from
> providing the needed space even when there is enough free space in a
> small ocfs2 volume.
> This patch gives ocfs2 the ability to reclaim suballoc free space when
> the block group is freed. For performance reasons, this patch keeps
> the first suballocator block group.
> 
> Signed-off-by: Heming Zhao <heming.zhao@suse.com>
> Reviewed-by: Su Yue <glass.su@suse.com>
> ---
>  fs/ocfs2/suballoc.c | 302 ++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 292 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index f7b483f0de2a..d62010166c34 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -294,6 +294,68 @@ static int ocfs2_validate_group_descriptor(struct super_block *sb,
>  	return ocfs2_validate_gd_self(sb, bh, 0);
>  }
>  
> +/*
> + * hint gd may already be released in _ocfs2_free_suballoc_bits(),
> + * we first check gd descriptor signature, then do the
> + * ocfs2_read_group_descriptor() jobs.
> + *
> + * When the group descriptor is invalid, we return 'rc=0' and
> + * '*released=1'. The caller should handle this case. Otherwise,
> + * we return the real error code.
> + */
> +static int ocfs2_read_hint_group_descriptor(struct inode *inode,
> +			struct ocfs2_dinode *di, u64 gd_blkno,
> +			struct buffer_head **bh, int *released)
> +{
> +	int rc;
> +	struct buffer_head *tmp = *bh;
> +	struct ocfs2_group_desc *gd;
> +
> +	*released = 0;

I'd like the caller is responsible for the initialization.

> +
> +	rc = ocfs2_read_block(INODE_CACHE(inode), gd_blkno, &tmp, NULL);
> +	if (rc)
> +		goto out;
> +
> +	gd = (struct ocfs2_group_desc *) tmp->b_data;
> +	if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {

How to distinguish the release case or a bug?

> +		/*
> +		 * Invalid gd cache was set in ocfs2_read_block(),
> +		 * which will affect block_group allocation.
> +		 * Path:
> +		 * ocfs2_reserve_suballoc_bits
> +		 *  ocfs2_block_group_alloc
> +		 *   ocfs2_block_group_alloc_contig
> +		 *    ocfs2_set_new_buffer_uptodate
> +		 */
> +		ocfs2_remove_from_cache(INODE_CACHE(inode), tmp);
> +		*released = 1; /* we return 'rc=0' for this case */
> +		goto free_bh;
> +	}
> +
> +	/* below jobs same with ocfs2_read_group_descriptor() */
> +	if (!buffer_jbd(tmp)) {
> +		rc = ocfs2_validate_group_descriptor(inode->i_sb, tmp);
> +		if (rc)
> +			goto free_bh;
> +	}
> +
> +	rc = ocfs2_validate_gd_parent(inode->i_sb, di, tmp, 0);
> +	if (rc)
> +		goto free_bh;
> +
> +	/* If ocfs2_read_block() got us a new bh, pass it up. */
> +	if (!*bh)
> +		*bh = tmp;
> +
> +	return rc;
> +
> +free_bh:
> +	brelse(tmp);
> +out:
> +	return rc;
> +}
> +
>  int ocfs2_read_group_descriptor(struct inode *inode, struct ocfs2_dinode *di,
>  				u64 gd_blkno, struct buffer_head **bh)
>  {
> @@ -1722,7 +1784,7 @@ static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
>  				  u32 bits_wanted,
>  				  u32 min_bits,
>  				  struct ocfs2_suballoc_result *res,
> -				  u16 *bits_left)
> +				  u16 *bits_left, int *released)
>  {
>  	int ret;
>  	struct buffer_head *group_bh = NULL;
> @@ -1730,9 +1792,11 @@ static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
>  	struct ocfs2_dinode *di = (struct ocfs2_dinode *)ac->ac_bh->b_data;
>  	struct inode *alloc_inode = ac->ac_inode;
>  
> -	ret = ocfs2_read_group_descriptor(alloc_inode, di,
> -					  res->sr_bg_blkno, &group_bh);
> -	if (ret < 0) {
> +	ret = ocfs2_read_hint_group_descriptor(alloc_inode, di,
> +				res->sr_bg_blkno, &group_bh, released);
> +	if (*released) {
> +		return 0;
> +	} else if (ret < 0) {
>  		mlog_errno(ret);
>  		return ret;
>  	}
> @@ -1934,7 +1998,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
>  				     u32 min_bits,
>  				     struct ocfs2_suballoc_result *res)
>  {
> -	int status;
> +	int status, released;
>  	u16 victim, i;
>  	u16 bits_left = 0;
>  	u64 hint = ac->ac_last_group;
> @@ -1961,6 +2025,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
>  		goto bail;
>  	}
>  
> +	/* the hint bg may already be released, we quiet search this group. */
>  	res->sr_bg_blkno = hint;
>  	if (res->sr_bg_blkno) {
>  		/* Attempt to short-circuit the usual search mechanism
> @@ -1968,7 +2033,12 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
>  		 * allocation group. This helps us maintain some
>  		 * contiguousness across allocations. */
>  		status = ocfs2_search_one_group(ac, handle, bits_wanted,
> -						min_bits, res, &bits_left);
> +						min_bits, res, &bits_left,
> +						&released);
> +		if (released) {
> +			res->sr_bg_blkno = 0;
> +			goto chain_search;
> +		}
>  		if (!status)
>  			goto set_hint;
>  		if (status < 0 && status != -ENOSPC) {
> @@ -1976,7 +2046,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
>  			goto bail;
>  		}
>  	}
> -
> +chain_search:
>  	cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;
>  
>  	victim = ocfs2_find_victim_chain(cl);
> @@ -2077,6 +2147,12 @@ int ocfs2_claim_metadata(handle_t *handle,
>  	return status;
>  }
>  
> +/*
> + * after ocfs2 has the ability to release block group unused space,
> + * the ->ip_last_used_group may be invalid. so this function returns
> + * ac->ac_last_group need to verify.
> + * refer the 'hint' in ocfs2_claim_suballoc_bits() for more details.
> + */
>  static void ocfs2_init_inode_ac_group(struct inode *dir,
>  				      struct buffer_head *parent_di_bh,
>  				      struct ocfs2_alloc_context *ac)
> @@ -2514,6 +2590,197 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
>  	return status;
>  }
>  
> +/*
> + * Reclaim the suballocator managed space to main bitmap.
> + * This function first works on the suballocator then switch to the
> + * main bitmap.
> + *
> + * handle: The transaction handle
> + * alloc_inode: The suballoc inode
> + * alloc_bh: The buffer_head of suballoc inode
> + * group_bh: The group descriptor buffer_head of suballocator managed.
> + *           Caller should release the input group_bh.
> + */
> +static int _reclaim_to_main_bm(handle_t *handle,

Better to rename it to _ocfs2_reclaim_suballoc_to_main().

> +			struct inode *alloc_inode,
> +			struct buffer_head *alloc_bh,
> +			struct buffer_head *group_bh)
> +{
> +	int idx, status = 0;
> +	int i, next_free_rec, len = 0;
> +	__le16 old_bg_contig_free_bits = 0;
> +	u16 start_bit;
> +	u32 tmp_used;
> +	u64 bg_blkno, start_blk;
> +	unsigned int count;
> +	struct ocfs2_chain_rec *rec;
> +	struct buffer_head *main_bm_bh = NULL;
> +	struct inode *main_bm_inode = NULL;
> +	struct ocfs2_super *osb = OCFS2_SB(alloc_inode->i_sb);
> +	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) alloc_bh->b_data;
> +	struct ocfs2_chain_list *cl = &fe->id2.i_chain;
> +	struct ocfs2_group_desc *group = (struct ocfs2_group_desc *) group_bh->b_data;
> +
> +	idx = le16_to_cpu(group->bg_chain);
> +	rec = &(cl->cl_recs[idx]);
> +
> +	status = ocfs2_extend_trans(handle,
> +				ocfs2_calc_group_alloc_credits(osb->sb,
> +						 le16_to_cpu(cl->cl_cpg)));
> +	if (status) {
> +		mlog_errno(status);
> +		goto bail;
> +	}
> +	status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
> +					 alloc_bh, OCFS2_JOURNAL_ACCESS_WRITE);
> +	if (status < 0) {
> +		mlog_errno(status);
> +		goto bail;
> +	}
> +
> +	/*
> +	 * Only clear the suballocator rec item in-place.
> +	 *
> +	 * If idx is not the last, we don't compress (remove the empty item)
> +	 * the cl_recs[]. If not, we need to do lots jobs.
> +	 *
> +	 * Compress cl_recs[] code example:
> +	 * if (idx != cl->cl_next_free_rec - 1)
> +	 * 	memmove(&cl->cl_recs[idx], &cl->cl_recs[idx + 1],
> +	 * 		sizeof(struct ocfs2_chain_rec) *
> +	 * 		(cl->cl_next_free_rec - idx - 1));
> +	 * for(i = idx; i < cl->cl_next_free_rec-1; i++) {
> +	 * 	group->bg_chain = "later group->bg_chain";
> +	 * 	group->bg_blkno = xxx;
> +	 * 	... ...
> +	 * }
> +	 */
> +
> +	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_total);
> +	fe->id1.bitmap1.i_total = cpu_to_le32(tmp_used - le32_to_cpu(rec->c_total));
> +
> +	/* Substraction 1 for the block group itself */
> +	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
> +	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - 1);
> +
> +	tmp_used = le32_to_cpu(fe->i_clusters);
> +	fe->i_clusters = cpu_to_le32(tmp_used - le16_to_cpu(cl->cl_cpg));
> +
> +	spin_lock(&OCFS2_I(alloc_inode)->ip_lock);
> +	OCFS2_I(alloc_inode)->ip_clusters -= le32_to_cpu(fe->i_clusters);
> +	fe->i_size = cpu_to_le64(ocfs2_clusters_to_bytes(alloc_inode->i_sb,
> +					     le32_to_cpu(fe->i_clusters)));
> +	spin_unlock(&OCFS2_I(alloc_inode)->ip_lock);
> +	i_size_write(alloc_inode, le64_to_cpu(fe->i_size));
> +	alloc_inode->i_blocks = ocfs2_inode_sector_count(alloc_inode);
> +
> +	ocfs2_journal_dirty(handle, alloc_bh);
> +	ocfs2_update_inode_fsync_trans(handle, alloc_inode, 0);
> +
> +	start_blk = le64_to_cpu(rec->c_blkno);
> +	count = le32_to_cpu(rec->c_total) / le16_to_cpu(cl->cl_bpc);
> +
> +	/*
> +	 * If the rec is the last one, let's compress the chain list by
> +	 * removing the empty cl_recs[] at the end.
> +	 */
> +	next_free_rec = le16_to_cpu(cl->cl_next_free_rec);
> +	if (idx == (next_free_rec - 1)) {
> +		len++; /* the last item should be counted first */
> +		for (i = (next_free_rec - 2); i > 0; i--) {
> +			if (cl->cl_recs[i].c_free == cl->cl_recs[i].c_total)
> +				len++;
> +			else
> +				break;
> +		}
> +	}
> +	le16_add_cpu(&cl->cl_next_free_rec, -len);
> +
> +	rec->c_free = 0;
> +	rec->c_total = 0;
> +	rec->c_blkno = 0;
> +	ocfs2_remove_from_cache(INODE_CACHE(alloc_inode), group_bh);
> +	memset(group, 0, sizeof(struct ocfs2_group_desc));
> +
> +	/* prepare job for reclaim clusters */
> +	main_bm_inode = ocfs2_get_system_file_inode(osb,
> +						    GLOBAL_BITMAP_SYSTEM_INODE,
> +						    OCFS2_INVALID_SLOT);
> +	if (!main_bm_inode)
> +		goto bail; /* ignore the error in reclaim path */
> +
> +	inode_lock(main_bm_inode);
> +
> +	status = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 1);
> +	if (status < 0)
> +		goto free_bm_inode; /* ignore the error in reclaim path */
> +
> +	ocfs2_block_to_cluster_group(main_bm_inode, start_blk, &bg_blkno,
> +				     &start_bit);
> +	fe = (struct ocfs2_dinode *) main_bm_bh->b_data;
> +	cl = &fe->id2.i_chain;
> +	/* reuse group_bh, caller will release the input group_bh */
> +	group_bh = NULL;
> +
> +	/* reclaim clusters to global_bitmap */
> +	status = ocfs2_read_group_descriptor(main_bm_inode, fe, bg_blkno,
> +					     &group_bh);
> +	if (status < 0) {
> +		mlog_errno(status);
> +		goto free_bm_bh;
> +	}
> +	group = (struct ocfs2_group_desc *) group_bh->b_data;
> +
> +	if ((count + start_bit) > le16_to_cpu(group->bg_bits)) {
> +		ocfs2_error(alloc_inode->i_sb,
> +			"reclaim length (%d) beyands block group length (%d)",
> +			count + start_bit, le16_to_cpu(group->bg_bits));
> +		goto free_group_bh;
> +	}
> +
> +	old_bg_contig_free_bits = group->bg_contig_free_bits;
> +	status = ocfs2_block_group_clear_bits(handle, main_bm_inode,
> +					      group, group_bh,
> +					      start_bit, count, 0,
> +					      _ocfs2_clear_bit);
> +	if (status < 0) {
> +		mlog_errno(status);
> +		goto free_group_bh;
> +	}
> +
> +	status = ocfs2_journal_access_di(handle, INODE_CACHE(main_bm_inode),
> +					 main_bm_bh, OCFS2_JOURNAL_ACCESS_WRITE);
> +	if (status < 0) {
> +		mlog_errno(status);
> +		ocfs2_block_group_set_bits(handle, main_bm_inode, group, group_bh,
> +				start_bit, count,
> +				le16_to_cpu(old_bg_contig_free_bits), 1);
> +		goto free_group_bh;
> +	}
> +
> +	idx = le16_to_cpu(group->bg_chain);
> +	rec = &(cl->cl_recs[idx]);
> +
> +	le32_add_cpu(&rec->c_free, count);
> +	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
> +	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
> +	ocfs2_journal_dirty(handle, main_bm_bh);
> +
> +free_group_bh:
> +	brelse(group_bh);
> +
> +free_bm_bh:
> +	ocfs2_inode_unlock(main_bm_inode, 1);
> +	brelse(main_bm_bh);
> +
> +free_bm_inode:
> +	inode_unlock(main_bm_inode);
> +	iput(main_bm_inode);
> +
> +bail:
> +	return status;
> +}
> +
>  /*
>   * expects the suballoc inode to already be locked.
>   */
> @@ -2526,12 +2793,13 @@ static int _ocfs2_free_suballoc_bits(handle_t *handle,
>  				     void (*undo_fn)(unsigned int bit,
>  						     unsigned long *bitmap))
>  {
> -	int status = 0;
> +	int idx, status = 0;
>  	u32 tmp_used;
>  	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) alloc_bh->b_data;
>  	struct ocfs2_chain_list *cl = &fe->id2.i_chain;
>  	struct buffer_head *group_bh = NULL;
>  	struct ocfs2_group_desc *group;
> +	struct ocfs2_chain_rec *rec;
>  	__le16 old_bg_contig_free_bits = 0;
>  
>  	/* The alloc_bh comes from ocfs2_free_dinode() or
> @@ -2577,12 +2845,26 @@ static int _ocfs2_free_suballoc_bits(handle_t *handle,
>  		goto bail;
>  	}
>  
> -	le32_add_cpu(&cl->cl_recs[le16_to_cpu(group->bg_chain)].c_free,
> -		     count);
> +	idx = le16_to_cpu(group->bg_chain);
> +	rec = &(cl->cl_recs[idx]);
> +
> +	le32_add_cpu(&rec->c_free, count);
>  	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
>  	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
>  	ocfs2_journal_dirty(handle, alloc_bh);
>  
> +	/*
> +	 * Reclaim suballocator free space.
> +	 * Bypass: global_bitmap, not empty rec, first rec in cl_recs[]

s/not empty rec/non empty rec

Thanks,
Joseph

> +	 */
> +	if (ocfs2_is_cluster_bitmap(alloc_inode) ||
> +	    (le32_to_cpu(rec->c_free) != (le32_to_cpu(rec->c_total) - 1)) ||
> +	    (le16_to_cpu(cl->cl_next_free_rec) == 1)) {
> +		goto bail;
> +	}
> +
> +	_reclaim_to_main_bm(handle, alloc_inode, alloc_bh, group_bh);
> +
>  bail:
>  	brelse(group_bh);
>  	return status;

On 10/8/24 15:16, Joseph Qi wrote:
> 
> 
> On 9/8/24 10:07 PM, Heming Zhao wrote:
>> The current ocfs2 code can't reclaim suballocator block group space.
>> This cause ocfs2 to hold onto a lot of space in some cases. for example,
>> when creating lots of small files, the space is held/managed by
>> '//inode_alloc'. After the user deletes all the small files, the space
>> never returns to '//global_bitmap'. This issue prevents ocfs2 from
>> providing the needed space even when there is enough free space in a
>> small ocfs2 volume.
>> This patch gives ocfs2 the ability to reclaim suballoc free space when
>> the block group is freed. For performance reasons, this patch keeps
>> the first suballocator block group.
>>
>> Signed-off-by: Heming Zhao <heming.zhao@suse.com>
>> Reviewed-by: Su Yue <glass.su@suse.com>
>> ---
>>   fs/ocfs2/suballoc.c | 302 ++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 292 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
>> index f7b483f0de2a..d62010166c34 100644
>> --- a/fs/ocfs2/suballoc.c
>> +++ b/fs/ocfs2/suballoc.c
>> @@ -294,6 +294,68 @@ static int ocfs2_validate_group_descriptor(struct super_block *sb,
>>   	return ocfs2_validate_gd_self(sb, bh, 0);
>>   }
>>   
>> +/*
>> + * hint gd may already be released in _ocfs2_free_suballoc_bits(),
>> + * we first check gd descriptor signature, then do the
>> + * ocfs2_read_group_descriptor() jobs.
>> + *
>> + * When the group descriptor is invalid, we return 'rc=0' and
>> + * '*released=1'. The caller should handle this case. Otherwise,
>> + * we return the real error code.
>> + */
>> +static int ocfs2_read_hint_group_descriptor(struct inode *inode,
>> +			struct ocfs2_dinode *di, u64 gd_blkno,
>> +			struct buffer_head **bh, int *released)
>> +{
>> +	int rc;
>> +	struct buffer_head *tmp = *bh;
>> +	struct ocfs2_group_desc *gd;
>> +
>> +	*released = 0;
> 
> I'd like the caller is responsible for the initialization.

OK.

> 
>> +
>> +	rc = ocfs2_read_block(INODE_CACHE(inode), gd_blkno, &tmp, NULL);
>> +	if (rc)
>> +		goto out;
>> +
>> +	gd = (struct ocfs2_group_desc *) tmp->b_data;
>> +	if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
> 
> How to distinguish the release case or a bug?

Good question.

Before this patch, OCFS2 never releases suballocator space.
The ocfs2_read_group_descriptor() doesn't need to handle the
case of reading a bad 'struct ocfs2_group_desc'.

After this patch, there is a gap between
_ocfs2_free_suballoc_bits() and ocfs2_read_hint_group_descriptor().


      thread A                          thread B
-------------------------------------------------------------
ocfs2_claim_suballoc_bits
  hint is not zero
   ocfs2_search_one_group
    + ocfs2_read_hint_group_descriptor
    | + OCFS2_IS_VALID_GROUP_DESC(gd)
    |    returns true
    |                                _ocfs2_free_suballoc_bits
    + ...                             + free the last bit of gd
    |                                    + release gd
    + ocfs2_block_group_set_bits
       uses released gd, data corruption
--------------------------------------------------------------

I plan to introduce a new cache_info flag 'OCFS2_CACHE_CLEAN_GD' to protect this case.
e.g. (just demo, not tested)


      thread A                          thread B
-------------------------------------------------------------
ocfs2_read_hint_group_descriptor()
   ocfs2_read_block()

   //protect code begin
   ci = INODE_CACHE(inode);
   ocfs2_metadata_cache_io_lock(ci);
   if (ci->ci_flags & OCFS2_CACHE_CLEAN_GD)
       goto free_bh;
   ocfs2_metadata_cache_io_unlock(ci);
   //protect code end

   gd = (struct ocfs2_group_desc *) tmp->b_data;
   if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
      ... ...
   }

                               _ocfs2_free_suballoc_bits()
                                 ... ...
                                 if (ocfs2_is_cluster_bitmap(alloc_inode) ||
                                     (le32_to_cpu(rec->c_free) != (le32_to_cpu(rec->c_total) - 1)) ||
                                     (le16_to_cpu(cl->cl_next_free_rec) == 1)) {
                                         goto bail;
                                 }

                                 //protect code begin
                                 ci = INODE_CACHE(alloc_inode);
                                 ocfs2_metadata_cache_io_lock(ci);
                                 if (ci->ci_num_cached > 1) {
                                         goto bail;
                                 }
                                 ci->ci_flags |= OCFS2_CACHE_CLEAN_GD;
                                 ocfs2_metadata_cache_io_unlock(ci);
                                 //protect code end

                                 _ocfs2_reclaim_suballoc_to_main(handle, alloc_inode, alloc_bh, group_bh);
--------------------------------------------------------------

> 
>> +		/*
>> +		 * Invalid gd cache was set in ocfs2_read_block(),
>> ... ...
>>   
>> +/*
>> + * Reclaim the suballocator managed space to main bitmap.
>> + * This function first works on the suballocator then switch to the
>> + * main bitmap.
>> + *
>> + * handle: The transaction handle
>> + * alloc_inode: The suballoc inode
>> + * alloc_bh: The buffer_head of suballoc inode
>> + * group_bh: The group descriptor buffer_head of suballocator managed.
>> + *           Caller should release the input group_bh.
>> + */
>> +static int _reclaim_to_main_bm(handle_t *handle,
> 
> Better to rename it to _ocfs2_reclaim_suballoc_to_main().

OK.
> 
>> +			struct inode *alloc_inode,
>> +			struct buffer_head *alloc_bh,
>> +			struct buffer_head *group_bh)
>> +{
>> +	int idx, status = 0;
>> +	int i, next_free_rec, len = 0;
>> +	__le16 old_bg_contig_free_bits = 0;
>> ... ...
>> +	le32_add_cpu(&rec->c_free, count);
>>   	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
>>   	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
>>   	ocfs2_journal_dirty(handle, alloc_bh);
>>   
>> +	/*
>> +	 * Reclaim suballocator free space.
>> +	 * Bypass: global_bitmap, not empty rec, first rec in cl_recs[]
> 
> s/not empty rec/non empty rec

OK.

/Heming

Hi Joseph,

Sorry for waking up this thread. Please see my comments below.

On Wed, Oct 09, 2024 at 10:56:47AM +0800, Heming Zhao wrote:
> On 10/8/24 15:16, Joseph Qi wrote:
> > 
> > 
> > On 9/8/24 10:07 PM, Heming Zhao wrote:
> > > The current ocfs2 code can't reclaim suballocator block group space.
> > > This cause ocfs2 to hold onto a lot of space in some cases. for example,
> > > when creating lots of small files, the space is held/managed by
> > > '//inode_alloc'. After the user deletes all the small files, the space
> > > never returns to '//global_bitmap'. This issue prevents ocfs2 from
> > > providing the needed space even when there is enough free space in a
> > > small ocfs2 volume.
> > > This patch gives ocfs2 the ability to reclaim suballoc free space when
> > > the block group is freed. For performance reasons, this patch keeps
> > > the first suballocator block group.
> > > 
> > > Signed-off-by: Heming Zhao <heming.zhao@suse.com>
> > > Reviewed-by: Su Yue <glass.su@suse.com>
> > > ---
> > >   fs/ocfs2/suballoc.c | 302 ++++++++++++++++++++++++++++++++++++++++++--
> > >   1 file changed, 292 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> > > index f7b483f0de2a..d62010166c34 100644
> > > --- a/fs/ocfs2/suballoc.c
> > > +++ b/fs/ocfs2/suballoc.c
> > > @@ -294,6 +294,68 @@ static int ocfs2_validate_group_descriptor(struct super_block *sb,
> > >   	return ocfs2_validate_gd_self(sb, bh, 0);
> > >   }
> > > +/*
> > > + * hint gd may already be released in _ocfs2_free_suballoc_bits(),
> > > + * we first check gd descriptor signature, then do the
> > > + * ocfs2_read_group_descriptor() jobs.
> > > + *
> > > + * When the group descriptor is invalid, we return 'rc=0' and
> > > + * '*released=1'. The caller should handle this case. Otherwise,
> > > + * we return the real error code.
> > > + */
> > > +static int ocfs2_read_hint_group_descriptor(struct inode *inode,
> > > +			struct ocfs2_dinode *di, u64 gd_blkno,
> > > +			struct buffer_head **bh, int *released)
> > > +{
> > > +	int rc;
> > > +	struct buffer_head *tmp = *bh;
> > > +	struct ocfs2_group_desc *gd;
> > > +
> > > +	*released = 0;
> > 
> > I'd like the caller is responsible for the initialization.
> 
> OK.
> 
> > 
> > > +
> > > +	rc = ocfs2_read_block(INODE_CACHE(inode), gd_blkno, &tmp, NULL);
> > > +	if (rc)
> > > +		goto out;
> > > +
> > > +	gd = (struct ocfs2_group_desc *) tmp->b_data;
> > > +	if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
> > 
> > How to distinguish the release case or a bug?
> 

I rechecked the code and withdraw my previous comments, as the release gap
doesn't exist.
The reason: ocfs2 locks alloc_inode before calling threads A and B.

Redarding the question: How to distinguish the release case or a bug?

(Hope I correctly understand your question) my answer:
ocfs2_read_hint_group_descriptor is derived from ocfs2_read_group_descriptor.
The differ is:
- ocfs2_read_group_descriptor calls ocfs2_read_block() and passes the
  'validate':ocfs2_validate_group_descriptor.
- ocfs2_read_hint_group_descriptor calls ocfs2_read_block and passes the 
  'validate':null

The job of distinguishing between a release case or a bug is similar to that of
ocfs2_read_group_descriptor. I directly call ocfs2_validate_group_descriptor
and ocfs2_validate_gd_parent after the GD signature is correct. If we
encounter a bug case, the subsequent validation functions will handle it.
Btw, in the new function _reclaim_to_main_bm(), the
memset(group, 0, sizeof(struct ocfs2_group_desc)) will clean up all group info.
Therefore, after applying this patch, the GD area is full with ZEROs after being
released.

Why can't we reuse the existing ocfs2_validate_group_descriptor()?
It calls ocfs2_validate_gd_self(), which triggers do_error() and makes the volume
read-only.

Thanks,
Heming

> Good question.
> 
> Before this patch, OCFS2 never releases suballocator space.
> The ocfs2_read_group_descriptor() doesn't need to handle the
> case of reading a bad 'struct ocfs2_group_desc'.
> 
> After this patch, there is a gap between
> _ocfs2_free_suballoc_bits() and ocfs2_read_hint_group_descriptor().
> 
> 
>      thread A                          thread B
> -------------------------------------------------------------
> ocfs2_claim_suballoc_bits
>  hint is not zero
>   ocfs2_search_one_group
>    + ocfs2_read_hint_group_descriptor
>    | + OCFS2_IS_VALID_GROUP_DESC(gd)
>    |    returns true
>    |                                _ocfs2_free_suballoc_bits
>    + ...                             + free the last bit of gd
>    |                                    + release gd
>    + ocfs2_block_group_set_bits
>       uses released gd, data corruption
> --------------------------------------------------------------
> 
> I plan to introduce a new cache_info flag 'OCFS2_CACHE_CLEAN_GD' to protect this case.
> e.g. (just demo, not tested)
> 
> 
>      thread A                          thread B
> -------------------------------------------------------------
> ocfs2_read_hint_group_descriptor()
>   ocfs2_read_block()
> 
>   //protect code begin
>   ci = INODE_CACHE(inode);
>   ocfs2_metadata_cache_io_lock(ci);
>   if (ci->ci_flags & OCFS2_CACHE_CLEAN_GD)
>       goto free_bh;
>   ocfs2_metadata_cache_io_unlock(ci);
>   //protect code end
> 
>   gd = (struct ocfs2_group_desc *) tmp->b_data;
>   if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
>      ... ...
>   }
> 
>                               _ocfs2_free_suballoc_bits()
>                                 ... ...
>                                 if (ocfs2_is_cluster_bitmap(alloc_inode) ||
>                                     (le32_to_cpu(rec->c_free) != (le32_to_cpu(rec->c_total) - 1)) ||
>                                     (le16_to_cpu(cl->cl_next_free_rec) == 1)) {
>                                         goto bail;
>                                 }
> 
>                                 //protect code begin
>                                 ci = INODE_CACHE(alloc_inode);
>                                 ocfs2_metadata_cache_io_lock(ci);
>                                 if (ci->ci_num_cached > 1) {
>                                         goto bail;
>                                 }
>                                 ci->ci_flags |= OCFS2_CACHE_CLEAN_GD;
>                                 ocfs2_metadata_cache_io_unlock(ci);
>                                 //protect code end
> 
>                                 _ocfs2_reclaim_suballoc_to_main(handle, alloc_inode, alloc_bh, group_bh);
> --------------------------------------------------------------
> 
> > 
> > > +		/*
> > > +		 * Invalid gd cache was set in ocfs2_read_block(),
> > > ... ...
> > > +/*
> > > + * Reclaim the suballocator managed space to main bitmap.
> > > + * This function first works on the suballocator then switch to the
> > > + * main bitmap.
> > > + *
> > > + * handle: The transaction handle
> > > + * alloc_inode: The suballoc inode
> > > + * alloc_bh: The buffer_head of suballoc inode
> > > + * group_bh: The group descriptor buffer_head of suballocator managed.
> > > + *           Caller should release the input group_bh.
> > > + */
> > > +static int _reclaim_to_main_bm(handle_t *handle,
> > 
> > Better to rename it to _ocfs2_reclaim_suballoc_to_main().
> 
> OK.
> > 
> > > +			struct inode *alloc_inode,
> > > +			struct buffer_head *alloc_bh,
> > > +			struct buffer_head *group_bh)
> > > +{
> > > +	int idx, status = 0;
> > > +	int i, next_free_rec, len = 0;
> > > +	__le16 old_bg_contig_free_bits = 0;
> > > ... ...
> > > +	le32_add_cpu(&rec->c_free, count);
> > >   	tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
> > >   	fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);
> > >   	ocfs2_journal_dirty(handle, alloc_bh);
> > > +	/*
> > > +	 * Reclaim suballocator free space.
> > > +	 * Bypass: global_bitmap, not empty rec, first rec in cl_recs[]
> > 
> > s/not empty rec/non empty rec
> 
> OK.
> 
> /Heming

On 9/8/24 22:07, Heming Zhao wrote:
> The current ocfs2 code can't reclaim suballocator block group space.
> This cause ocfs2 to hold onto a lot of space in some cases. for example,
> when creating lots of small files, the space is held/managed by
> '//inode_alloc'. After the user deletes all the small files, the space
> never returns to '//global_bitmap'. This issue prevents ocfs2 from
> providing the needed space even when there is enough free space in a
> small ocfs2 volume.
> This patch gives ocfs2 the ability to reclaim suballoc free space when
> the block group is freed. For performance reasons, this patch keeps
> the first suballocator block group.
> 
> Signed-off-by: Heming Zhao <heming.zhao@suse.com>
> Reviewed-by: Su Yue <glass.su@suse.com>
> ---
>   fs/ocfs2/suballoc.c | 302 ++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 292 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index f7b483f0de2a..d62010166c34 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> ... ...
>   
> +/*
> + * Reclaim the suballocator managed space to main bitmap.
> + * This function first works on the suballocator then switch to the
> + * main bitmap.

need to revise above comment:
This function first works on the suballocator to perform the
cleanup rec/alloc_inode job, then switches to the main bitmap
to reclaim released space.

-Heming

> + *
> + * handle: The transaction handle
> + * alloc_inode: The suballoc inode
> + * alloc_bh: The buffer_head of suballoc inode
> + * group_bh: The group descriptor buffer_head of suballocator managed.
> + *           Caller should release the input group_bh.
> + */
> +static int _reclaim_to_main_bm(handle_t *handle,
> +			struct inode *alloc_inode,
> +			struct buffer_head *alloc_bh,
> +			struct buffer_head *group_bh)
> +{