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Subject: Re: [PATCH v5 2/2] ext4: limit the length of per-inode prealloc list
To:     brookxu <brookxu.cn@gmail.com>, adilger.kernel@dilger.ca,
        tytso@mit.edu
Cc:     jack@suse.cz, linux-ext4@vger.kernel.org
References: <d7a98178-056b-6db5-6bce-4ead23f4a257@gmail.com>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Tue, 18 Aug 2020 08:39:57 +0530
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On 8/17/20 1:06 PM, brookxu wrote:
> In the scenario of writing sparse files, the per-inode prealloc list may
> be very long, resulting in high overhead for ext4_mb_use_preallocated().
> To circumvent this problem, we limit the maximum length of per-inode
> prealloc list to 512 and allow users to modify it.
> 
> After patching, we observed that the sys ratio of cpu has dropped, and
> the system throughput has increased significantly. We created a process
> to write the sparse file, and the running time of the process on the
> fixed kernel was significantly reduced, as follows:
> 
> Running time on unfixed kernel：
> [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
> real    0m2.051s
> user    0m0.008s
> sys     0m2.026s
> 
> Running time on fixed kernel：
> [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
> real    0m0.471s
> user    0m0.004s
> sys     0m0.395s
> 
> V5:
> 1. Fix the wrong parameter of list_move().
> 2. Use an atomic variable to count the length of the prealloc list.
> 
> V4:
> 1. Add performance data to the commit log.
> 
> Signed-off-by: Chunguang Xu <brookxu@tencent.com>
> ---
>   Documentation/admin-guide/ext4.rst |  3 ++
>   fs/ext4/ext4.h                     |  4 ++-
>   fs/ext4/extents.c                  | 10 +++---
>   fs/ext4/file.c                     |  2 +-
>   fs/ext4/indirect.c                 |  2 +-
>   fs/ext4/inode.c                    |  6 ++--
>   fs/ext4/ioctl.c                    |  2 +-
>   fs/ext4/mballoc.c                  | 74 +++++++++++++++++++++++++++++++++-----
>   fs/ext4/mballoc.h                  |  4 +++
>   fs/ext4/move_extent.c              |  4 +--
>   fs/ext4/super.c                    |  3 +-
>   fs/ext4/sysfs.c                    |  2 ++
>   include/trace/events/ext4.h        | 17 +++++----
>   13 files changed, 104 insertions(+), 29 deletions(-)
> 
> diff --git a/Documentation/admin-guide/ext4.rst b/Documentation/admin-guide/ext4.rst
> index 9443fce..f37d074 100644
> --- a/Documentation/admin-guide/ext4.rst
> +++ b/Documentation/admin-guide/ext4.rst
> @@ -482,6 +482,9 @@ Files in /sys/fs/ext4/<devname>:
>           multiple of this tuning parameter if the stripe size is not set in the
>           ext4 superblock
>   
> +  mb_max_inode_prealloc
> +        The maximum length of per-inode ext4_prealloc_space list.
> +
>     mb_max_to_scan
>           The maximum number of extents the multiblock allocator will search to
>           find the best extent.
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 42f5060..c4b465c 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1054,6 +1054,7 @@ struct ext4_inode_info {
>   	struct timespec64 i_crtime;
>   
>   	/* mballoc */
> +	atomic_t i_prealloc_active;
>   	struct list_head i_prealloc_list;
>   	spinlock_t i_prealloc_lock;
>   
> @@ -1501,6 +1502,7 @@ struct ext4_sb_info {
>   	unsigned int s_mb_stats;
>   	unsigned int s_mb_order2_reqs;
>   	unsigned int s_mb_group_prealloc;
> +	unsigned int s_mb_max_inode_prealloc;
>   	unsigned int s_max_dir_size_kb;
>   	/* where last allocation was done - for stream allocation */
>   	unsigned long s_mb_last_group;
> @@ -2651,7 +2653,7 @@ extern int ext4_init_inode_table(struct super_block *sb,
>   extern ext4_fsblk_t ext4_mb_new_blocks(handle_t *,
>   				struct ext4_allocation_request *, int *);
>   extern int ext4_mb_reserve_blocks(struct super_block *, int);
> -extern void ext4_discard_preallocations(struct inode *);
> +extern void ext4_discard_preallocations(struct inode *, unsigned int);
>   extern int __init ext4_init_mballoc(void);
>   extern void ext4_exit_mballoc(void);
>   extern void ext4_free_blocks(handle_t *handle, struct inode *inode,
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 221f240..a40f928 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -100,7 +100,7 @@ static int ext4_ext_trunc_restart_fn(struct inode *inode, int *dropped)
>   	 * i_mutex. So we can safely drop the i_data_sem here.
>   	 */
>   	BUG_ON(EXT4_JOURNAL(inode) == NULL);
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   	up_write(&EXT4_I(inode)->i_data_sem);
>   	*dropped = 1;
>   	return 0;
> @@ -4272,7 +4272,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>   			 * not a good idea to call discard here directly,
>   			 * but otherwise we'd need to call it every free().
>   			 */
> -			ext4_discard_preallocations(inode);
> +			ext4_discard_preallocations(inode, 0);
>   			if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
>   				fb_flags = EXT4_FREE_BLOCKS_NO_QUOT_UPDATE;
>   			ext4_free_blocks(handle, inode, NULL, newblock,
> @@ -5299,7 +5299,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>   	}
>   
>   	down_write(&EXT4_I(inode)->i_data_sem);
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   
>   	ret = ext4_es_remove_extent(inode, punch_start,
>   				    EXT_MAX_BLOCKS - punch_start);
> @@ -5313,7 +5313,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>   		up_write(&EXT4_I(inode)->i_data_sem);
>   		goto out_stop;
>   	}
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   
>   	ret = ext4_ext_shift_extents(inode, handle, punch_stop,
>   				     punch_stop - punch_start, SHIFT_LEFT);
> @@ -5445,7 +5445,7 @@ static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
>   		goto out_stop;
>   
>   	down_write(&EXT4_I(inode)->i_data_sem);
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   
>   	path = ext4_find_extent(inode, offset_lblk, NULL, 0);
>   	if (IS_ERR(path)) {
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 2a01e31..e3ab8ea 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -148,7 +148,7 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
>   		        !EXT4_I(inode)->i_reserved_data_blocks)
>   	{
>   		down_write(&EXT4_I(inode)->i_data_sem);
> -		ext4_discard_preallocations(inode);
> +		ext4_discard_preallocations(inode, 0);
>   		up_write(&EXT4_I(inode)->i_data_sem);
>   	}
>   	if (is_dx(inode) && filp->private_data)
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index be2b66e..ec6b930 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -696,7 +696,7 @@ static int ext4_ind_trunc_restart_fn(handle_t *handle, struct inode *inode,
>   	 * i_mutex. So we can safely drop the i_data_sem here.
>   	 */
>   	BUG_ON(EXT4_JOURNAL(inode) == NULL);
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   	up_write(&EXT4_I(inode)->i_data_sem);
>   	*dropped = 1;
>   	return 0;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 10dd470..bb9e1cd 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -383,7 +383,7 @@ void ext4_da_update_reserve_space(struct inode *inode,
>   	 */
>   	if ((ei->i_reserved_data_blocks == 0) &&
>   	    !inode_is_open_for_write(inode))
> -		ext4_discard_preallocations(inode);
> +		ext4_discard_preallocations(inode, 0);
>   }
>   
>   static int __check_block_validity(struct inode *inode, const char *func,
> @@ -4056,7 +4056,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>   	if (stop_block > first_block) {
>   
>   		down_write(&EXT4_I(inode)->i_data_sem);
> -		ext4_discard_preallocations(inode);
> +		ext4_discard_preallocations(inode, 0);
>   
>   		ret = ext4_es_remove_extent(inode, first_block,
>   					    stop_block - first_block);
> @@ -4211,7 +4211,7 @@ int ext4_truncate(struct inode *inode)
>   
>   	down_write(&EXT4_I(inode)->i_data_sem);
>   
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   
>   	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
>   		err = ext4_ext_truncate(handle, inode);
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 999cf6a..a5fcc23 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -202,7 +202,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
>   	reset_inode_seed(inode);
>   	reset_inode_seed(inode_bl);
>   
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   
>   	err = ext4_mark_inode_dirty(handle, inode);
>   	if (err < 0) {
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 51f37f1..58426c6 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2739,6 +2739,7 @@ int ext4_mb_init(struct super_block *sb)
>   	sbi->s_mb_stats = MB_DEFAULT_STATS;
>   	sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
>   	sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
> +	sbi->s_mb_max_inode_prealloc = MB_DEFAULT_MAX_INODE_PREALLOC;
>   	/*
>   	 * The default group preallocation is 512, which for 4k block
>   	 * sizes translates to 2 megabytes.  However for bigalloc file
> @@ -3677,6 +3678,26 @@ void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
>   	mb_debug(sb, "preallocated %d for group %u\n", preallocated, group);
>   }
>   
> +static void ext4_mb_mark_pa_deleted(struct super_block *sb,
> +				    struct ext4_prealloc_space *pa)
> +{
> +	struct ext4_inode_info *ei;
> +
> +	if (pa->pa_deleted) {
> +		ext4_warning(sb, "deaded pa, type:%d, pblk:%llu, lblk:%u, len:%d\n",

s/deaded/deleted ?


> +			     pa->pa_type, pa->pa_pstart, pa->pa_lstart,
> +			     pa->pa_len);
> +		return;
> +	}
> +
> +	pa->pa_deleted = 1;
> +
> +	if (pa->pa_type == MB_INODE_PA) {
> +		ei = EXT4_I(pa->pa_inode);
> +		atomic_dec(&ei->i_prealloc_active);
> +	}
> +}
> +
>   static void ext4_mb_pa_callback(struct rcu_head *head)
>   {
>   	struct ext4_prealloc_space *pa;
> @@ -3709,7 +3730,7 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
>   		return;
>   	}
>   
> -	pa->pa_deleted = 1;
> +	ext4_mb_mark_pa_deleted(sb, pa);
>   	spin_unlock(&pa->pa_lock);
>   
>   	grp_blk = pa->pa_pstart;
> @@ -3833,6 +3854,7 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
>   	spin_lock(pa->pa_obj_lock);
>   	list_add_rcu(&pa->pa_inode_list, &ei->i_prealloc_list);
>   	spin_unlock(pa->pa_obj_lock);
> +	atomic_inc(&ei->i_prealloc_active);
>   }
>   
>   /*
> @@ -4043,7 +4065,7 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
>   		}
>   
>   		/* seems this one can be freed ... */
> -		pa->pa_deleted = 1;
> +		ext4_mb_mark_pa_deleted(sb, pa);
>   
>   		/* we can trust pa_free ... */
>   		free += pa->pa_free;
> @@ -4106,7 +4128,7 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
>    *
>    * FIXME!! Make sure it is valid at all the call sites
>    */
> -void ext4_discard_preallocations(struct inode *inode)
> +void ext4_discard_preallocations(struct inode *inode, unsigned int needed)
>   {
>   	struct ext4_inode_info *ei = EXT4_I(inode);
>   	struct super_block *sb = inode->i_sb;
> @@ -4124,15 +4146,19 @@ void ext4_discard_preallocations(struct inode *inode)
>   
>   	mb_debug(sb, "discard preallocation for inode %lu\n",
>   		 inode->i_ino);
> -	trace_ext4_discard_preallocations(inode);
> +	trace_ext4_discard_preallocations(inode,
> +			atomic_read(&ei->i_prealloc_active), needed);
>   
>   	INIT_LIST_HEAD(&list);
>   
> +	if (needed == 0)
> +		needed = UINT_MAX;
> +
>   repeat:
>   	/* first, collect all pa's in the inode */
>   	spin_lock(&ei->i_prealloc_lock);
> -	while (!list_empty(&ei->i_prealloc_list)) {
> -		pa = list_entry(ei->i_prealloc_list.next,
> +	while (!list_empty(&ei->i_prealloc_list) && needed) {
> +		pa = list_entry(ei->i_prealloc_list.prev,
>   				struct ext4_prealloc_space, pa_inode_list);
>   		BUG_ON(pa->pa_obj_lock != &ei->i_prealloc_lock);
>   		spin_lock(&pa->pa_lock);
> @@ -4149,10 +4175,11 @@ void ext4_discard_preallocations(struct inode *inode)
>   
>   		}
>   		if (pa->pa_deleted == 0) {
> -			pa->pa_deleted = 1;
> +			ext4_mb_mark_pa_deleted(sb, pa);
>   			spin_unlock(&pa->pa_lock);
>   			list_del_rcu(&pa->pa_inode_list);
>   			list_add(&pa->u.pa_tmp_list, &list);
> +			needed--;
>   			continue;
>   		}
>   
> @@ -4453,7 +4480,7 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
>   		BUG_ON(pa->pa_type != MB_GROUP_PA);
>   
>   		/* seems this one can be freed ... */
> -		pa->pa_deleted = 1;
> +		ext4_mb_mark_pa_deleted(sb, pa);

Isn't this inside ext4_mb_discard_lg_preallocations()?
ext4_mb_mark_pa_deleted() is not required here. Since there is anyway a
BUG_ON() at top which ensures that this is MB_GROUP_PA type only.

-ritesh


>   		spin_unlock(&pa->pa_lock);
>   
>   		list_del_rcu(&pa->pa_inode_list);
> @@ -4552,10 +4579,29 @@ static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
>   }
>   
>   /*
> + * if per-inode prealloc list is too long, trim some PA
> + */
> +static void ext4_mb_trim_inode_pa(struct inode *inode)
> +{
> +	struct ext4_inode_info *ei = EXT4_I(inode);
> +	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> +	int count, delta;
> +
> +	count = atomic_read(&ei->i_prealloc_active);
> +	delta = (sbi->s_mb_max_inode_prealloc >> 2) + 1;
> +	if (count > sbi->s_mb_max_inode_prealloc + delta) {
> +		count -= sbi->s_mb_max_inode_prealloc;
> +		ext4_discard_preallocations(inode, count);
> +	}
> +}
> +
> +/*
>    * release all resource we used in allocation
>    */
>   static int ext4_mb_release_context(struct ext4_allocation_context *ac)
>   {
> +	struct inode *inode = ac->ac_inode;
> +	struct ext4_inode_info *ei = EXT4_I(inode);
>   	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>   	struct ext4_prealloc_space *pa = ac->ac_pa;
>   	if (pa) {
> @@ -4581,6 +4627,17 @@ static int ext4_mb_release_context(struct ext4_allocation_context *ac)
>   				ext4_mb_add_n_trim(ac);
>   			}
>   		}
> +
> +		if (pa->pa_type == MB_INODE_PA) {
> +			/*
> +			 * treat per-inode prealloc list as a lru list, then try
> +			 * to trim the least recently used PA.
> +			 */
> +			spin_lock(pa->pa_obj_lock);
> +			list_move(&pa->pa_inode_list, &ei->i_prealloc_list);
> +			spin_unlock(pa->pa_obj_lock);
> +		}
> +
>   		ext4_mb_put_pa(ac, ac->ac_sb, pa);
>   	}
>   	if (ac->ac_bitmap_page)
> @@ -4590,6 +4647,7 @@ static int ext4_mb_release_context(struct ext4_allocation_context *ac)
>   	if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
>   		mutex_unlock(&ac->ac_lg->lg_mutex);
>   	ext4_mb_collect_stats(ac);
> +	ext4_mb_trim_inode_pa(inode);
>   	return 0;
>   }
>   
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> index 6b4d17c..e75b474 100644
> --- a/fs/ext4/mballoc.h
> +++ b/fs/ext4/mballoc.h
> @@ -73,6 +73,10 @@
>    */
>   #define MB_DEFAULT_GROUP_PREALLOC	512
>   
> +/*
> + * maximum length of inode prealloc list
> + */
> +#define MB_DEFAULT_MAX_INODE_PREALLOC	512
>   
>   struct ext4_free_data {
>   	/* this links the free block information from sb_info */
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index 1ed86fb..0d601b8 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -686,8 +686,8 @@
>   
>   out:
>   	if (*moved_len) {
> -		ext4_discard_preallocations(orig_inode);
> -		ext4_discard_preallocations(donor_inode);
> +		ext4_discard_preallocations(orig_inode, 0);
> +		ext4_discard_preallocations(donor_inode, 0);
>   	}
>   
>   	ext4_ext_drop_refs(path);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 330957e..4df5dde 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1123,6 +1123,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
>   	inode_set_iversion(&ei->vfs_inode, 1);
>   	spin_lock_init(&ei->i_raw_lock);
>   	INIT_LIST_HEAD(&ei->i_prealloc_list);
> +	atomic_set(&ei->i_prealloc_active, 0);
>   	spin_lock_init(&ei->i_prealloc_lock);
>   	ext4_es_init_tree(&ei->i_es_tree);
>   	rwlock_init(&ei->i_es_lock);
> @@ -1216,7 +1217,7 @@ void ext4_clear_inode(struct inode *inode)
>   {
>   	invalidate_inode_buffers(inode);
>   	clear_inode(inode);
> -	ext4_discard_preallocations(inode);
> +	ext4_discard_preallocations(inode, 0);
>   	ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
>   	dquot_drop(inode);
>   	if (EXT4_I(inode)->jinode) {
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index 6c9fc9e..92f04e9 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -215,6 +215,7 @@ static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)
>   EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
>   EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
>   EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> +EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
>   EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
>   EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
>   EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> @@ -257,6 +258,7 @@ static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)
>   	ATTR_LIST(mb_order2_req),
>   	ATTR_LIST(mb_stream_req),
>   	ATTR_LIST(mb_group_prealloc),
> +	ATTR_LIST(mb_max_inode_prealloc),
>   	ATTR_LIST(max_writeback_mb_bump),
>   	ATTR_LIST(extent_max_zeroout_kb),
>   	ATTR_LIST(trigger_fs_error),
> diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
> index cc41d69..628db6a 100644
> --- a/include/trace/events/ext4.h
> +++ b/include/trace/events/ext4.h
> @@ -746,24 +746,29 @@
>   );
>   
>   TRACE_EVENT(ext4_discard_preallocations,
> -	TP_PROTO(struct inode *inode),
> +	TP_PROTO(struct inode *inode, unsigned int len, unsigned int needed),
>   
> -	TP_ARGS(inode),
> +	TP_ARGS(inode, len, needed),
>   
>   	TP_STRUCT__entry(
> -		__field(	dev_t,	dev			)
> -		__field(	ino_t,	ino			)
> +		__field(	dev_t,		dev		)
> +		__field(	ino_t,		ino		)
> +		__field(	unsigned int,	len		)
> +		__field(	unsigned int,	needed		)
>   
>   	),
>   
>   	TP_fast_assign(
>   		__entry->dev	= inode->i_sb->s_dev;
>   		__entry->ino	= inode->i_ino;
> +		__entry->len	= len;
> +		__entry->needed	= needed;
>   	),
>   
> -	TP_printk("dev %d,%d ino %lu",
> +	TP_printk("dev %d,%d ino %lu len: %u needed %u",
>   		  MAJOR(__entry->dev), MINOR(__entry->dev),
> -		  (unsigned long) __entry->ino)
> +		  (unsigned long) __entry->ino, __entry->len,
> +		  __entry->needed)
>   );
>   
>   TRACE_EVENT(ext4_mb_discard_preallocations,
>