Re: [PATCH 2/2] xfs: streamline xfs_getfsmap performance

[Chandan Babu R <chandanrlinux@gmail.com>]

On Friday 2 October 2020 10:19:30 AM IST Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Refactor xfs_getfsmap to improve its performance: instead of indirectly
> calling a function that copies one record to userspace at a time, create
> a shadow buffer in the kernel and copy the whole array once at the end.
> This should speed it up significantly.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Overall code flow is logically correct.

Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
>  fs/xfs/xfs_fsmap.c |   35 +++++++++++++++-----------
>  fs/xfs/xfs_fsmap.h |    6 +----
>  fs/xfs/xfs_ioctl.c |   69 ++++++++++++++++++++++------------------------------
>  3 files changed, 50 insertions(+), 60 deletions(-)
> 
> 
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> index aa36e7daf82c..3f2666c62a60 100644
> --- a/fs/xfs/xfs_fsmap.c
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -155,8 +155,7 @@ xfs_fsmap_owner_from_rmap(
>  /* getfsmap query state */
>  struct xfs_getfsmap_info {
>  	struct xfs_fsmap_head	*head;
> -	xfs_fsmap_format_t	formatter;	/* formatting fn */
> -	void			*format_arg;	/* format buffer */
> +	struct fsmap		*fsmap_recs;	/* mapping records */
>  	struct xfs_buf		*agf_bp;	/* AGF, for refcount queries */
>  	xfs_daddr_t		next_daddr;	/* next daddr we expect */
>  	u64			missing_owner;	/* owner of holes */
> @@ -224,6 +223,20 @@ xfs_getfsmap_is_shared(
>  	return 0;
>  }
>  
> +static inline void
> +xfs_getfsmap_format(
> +	struct xfs_mount		*mp,
> +	struct xfs_fsmap		*xfm,
> +	struct xfs_getfsmap_info	*info)
> +{
> +	struct fsmap			*rec;
> +
> +	trace_xfs_getfsmap_mapping(mp, xfm);
> +
> +	rec = &info->fsmap_recs[info->head->fmh_entries++];
> +	xfs_fsmap_from_internal(rec, xfm);
> +}
> +
>  /*
>   * Format a reverse mapping for getfsmap, having translated rm_startblock
>   * into the appropriate daddr units.
> @@ -288,10 +301,7 @@ xfs_getfsmap_helper(
>  		fmr.fmr_offset = 0;
>  		fmr.fmr_length = rec_daddr - info->next_daddr;
>  		fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
> -		error = info->formatter(&fmr, info->format_arg);
> -		if (error)
> -			return error;
> -		info->head->fmh_entries++;
> +		xfs_getfsmap_format(mp, &fmr, info);
>  	}
>  
>  	if (info->last)
> @@ -323,11 +333,8 @@ xfs_getfsmap_helper(
>  		if (shared)
>  			fmr.fmr_flags |= FMR_OF_SHARED;
>  	}
> -	error = info->formatter(&fmr, info->format_arg);
> -	if (error)
> -		return error;
> -	info->head->fmh_entries++;
>  
> +	xfs_getfsmap_format(mp, &fmr, info);
>  out:
>  	rec_daddr += XFS_FSB_TO_BB(mp, rec->rm_blockcount);
>  	if (info->next_daddr < rec_daddr)
> @@ -796,7 +803,7 @@ xfs_getfsmap_check_keys(
>  
>  /*
>   * Get filesystem's extents as described in head, and format for
> - * output.  Calls formatter to fill the user's buffer until all
> + * output.  Calls xfs_getfsmap_format to fill the user's buffer until all
>   * extents are mapped, until the passed-in head->fmh_count slots have
>   * been filled, or until the formatter short-circuits the loop, if it
>   * is tracking filled-in extents on its own.
> @@ -819,8 +826,7 @@ int
>  xfs_getfsmap(
>  	struct xfs_mount		*mp,
>  	struct xfs_fsmap_head		*head,
> -	xfs_fsmap_format_t		formatter,
> -	void				*arg)
> +	struct fsmap			*fsmap_recs)
>  {
>  	struct xfs_trans		*tp = NULL;
>  	struct xfs_fsmap		dkeys[2];	/* per-dev keys */
> @@ -895,8 +901,7 @@ xfs_getfsmap(
>  
>  	info.next_daddr = head->fmh_keys[0].fmr_physical +
>  			  head->fmh_keys[0].fmr_length;
> -	info.formatter = formatter;
> -	info.format_arg = arg;
> +	info.fsmap_recs = fsmap_recs;
>  	info.head = head;
>  
>  	/*
> diff --git a/fs/xfs/xfs_fsmap.h b/fs/xfs/xfs_fsmap.h
> index c6c57739b862..a0775788e7b1 100644
> --- a/fs/xfs/xfs_fsmap.h
> +++ b/fs/xfs/xfs_fsmap.h
> @@ -27,13 +27,9 @@ struct xfs_fsmap_head {
>  	struct xfs_fsmap fmh_keys[2];	/* low and high keys */
>  };
>  
> -void xfs_fsmap_from_internal(struct fsmap *dest, struct xfs_fsmap *src);
>  void xfs_fsmap_to_internal(struct xfs_fsmap *dest, struct fsmap *src);
>  
> -/* fsmap to userspace formatter - copy to user & advance pointer */
> -typedef int (*xfs_fsmap_format_t)(struct xfs_fsmap *, void *);
> -
>  int xfs_getfsmap(struct xfs_mount *mp, struct xfs_fsmap_head *head,
> -		xfs_fsmap_format_t formatter, void *arg);
> +		struct fsmap *out_recs);
>  
>  #endif /* __XFS_FSMAP_H__ */
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index bca7659fb5c6..e0f2100b74b0 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1716,38 +1716,15 @@ xfs_ioc_getbmap(
>  	return error;
>  }
>  
> -struct getfsmap_info {
> -	struct xfs_mount	*mp;
> -	struct fsmap_head __user *data;
> -	unsigned int		idx;
> -	__u32			last_flags;
> -};
> -
> -STATIC int
> -xfs_getfsmap_format(struct xfs_fsmap *xfm, void *priv)
> -{
> -	struct getfsmap_info	*info = priv;
> -	struct fsmap		fm;
> -
> -	trace_xfs_getfsmap_mapping(info->mp, xfm);
> -
> -	info->last_flags = xfm->fmr_flags;
> -	xfs_fsmap_from_internal(&fm, xfm);
> -	if (copy_to_user(&info->data->fmh_recs[info->idx++], &fm,
> -			sizeof(struct fsmap)))
> -		return -EFAULT;
> -
> -	return 0;
> -}
> -
>  STATIC int
>  xfs_ioc_getfsmap(
>  	struct xfs_inode	*ip,
>  	struct fsmap_head	__user *arg)
>  {
> -	struct getfsmap_info	info = { NULL };
>  	struct xfs_fsmap_head	xhead = {0};
>  	struct fsmap_head	head;
> +	struct fsmap		*recs;
> +	unsigned int		count;
>  	bool			aborted = false;
>  	int			error;
>  
> @@ -1760,38 +1737,50 @@ xfs_ioc_getfsmap(
>  		       sizeof(head.fmh_keys[1].fmr_reserved)))
>  		return -EINVAL;
>  
> +	count = min_t(unsigned int, head.fmh_count,
> +			UINT_MAX / sizeof(struct fsmap));
> +	recs = kvzalloc(count * sizeof(struct fsmap), GFP_KERNEL);
> +	if (!recs)
> +		return -ENOMEM;
> +
>  	xhead.fmh_iflags = head.fmh_iflags;
> -	xhead.fmh_count = head.fmh_count;
> +	xhead.fmh_count = count;
>  	xfs_fsmap_to_internal(&xhead.fmh_keys[0], &head.fmh_keys[0]);
>  	xfs_fsmap_to_internal(&xhead.fmh_keys[1], &head.fmh_keys[1]);
>  
>  	trace_xfs_getfsmap_low_key(ip->i_mount, &xhead.fmh_keys[0]);
>  	trace_xfs_getfsmap_high_key(ip->i_mount, &xhead.fmh_keys[1]);
>  
> -	info.mp = ip->i_mount;
> -	info.data = arg;
> -	error = xfs_getfsmap(ip->i_mount, &xhead, xfs_getfsmap_format, &info);
> +	error = xfs_getfsmap(ip->i_mount, &xhead, recs);
>  	if (error == -ECANCELED) {
>  		error = 0;
>  		aborted = true;
>  	} else if (error)
> -		return error;
> -
> -	/* If we didn't abort, set the "last" flag in the last fmx */
> -	if (!aborted && info.idx) {
> -		info.last_flags |= FMR_OF_LAST;
> -		if (copy_to_user(&info.data->fmh_recs[info.idx - 1].fmr_flags,
> -				&info.last_flags, sizeof(info.last_flags)))
> -			return -EFAULT;
> -	}
> +		goto out_free;
>  
>  	/* copy back header */
> +	error = -EFAULT;
>  	head.fmh_entries = xhead.fmh_entries;
>  	head.fmh_oflags = xhead.fmh_oflags;
>  	if (copy_to_user(arg, &head, sizeof(struct fsmap_head)))
> -		return -EFAULT;
> +		goto out_free;
>  
> -	return 0;
> +	/* Copy records if userspace wasn't asking only for a record count. */
> +	if (head.fmh_count > 0) {
> +		/* If we didn't abort, set the "last" flag in the last record */
> +		if (!aborted && xhead.fmh_entries > 0)
> +			recs[xhead.fmh_entries - 1].fmr_flags |= FMR_OF_LAST;
> +
> +		/* Copy all records out to userspace. */
> +		if (copy_to_user(arg->fmh_recs, recs,
> +				 xhead.fmh_entries * sizeof(struct fsmap)))
> +			goto out_free;
> +	}
> +
> +	error = 0;
> +out_free:
> +	kmem_free(recs);
> +	return error;
>  }
>  
>  STATIC int
> 
> 


-- 
chandan