Re: [PATCH 22/43] xfs: add the zoned space allocator

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Feb 06, 2025 at 07:44:38AM +0100, Christoph Hellwig wrote:
> For zoned RT devices space is always allocated at the write pointer, that
> is right after the last written block and only recorded on I/O completion.
> 
> Because the actual allocation algorithm is very simple and just involves
> picking a good zone - preferably the one used for the last write to the
> inode.  As the number of zones that can written at the same time is
> usually limited by the hardware, selecting a zone is done as late as
> possible from the iomap dio and buffered writeback bio submissions
> helpers just before submitting the bio.
> 
> Given that the writers already took a reservation before acquiring the
> iolock, space will always be readily available if an open zone slot is
> available.  A new structure is used to track these open zones, and
> pointed to by the xfs_rtgroup.  Because zoned file systems don't have
> a rsum cache the space for that pointer can be reused.
> 
> Allocations are only recorded at I/O completion time.  The scheme used
> for that is very similar to the reflink COW end I/O path.
> 
> Co-developed-by: Hans Holmberg <hans.holmberg@wdc.com>
> Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/Makefile             |   3 +-
>  fs/xfs/libxfs/xfs_rtgroup.h |  22 +-
>  fs/xfs/libxfs/xfs_types.h   |  13 +-
>  fs/xfs/xfs_log.c            |   4 +
>  fs/xfs/xfs_mount.c          |  17 +-
>  fs/xfs/xfs_mount.h          |   2 +
>  fs/xfs/xfs_rtalloc.c        |   6 +-
>  fs/xfs/xfs_trace.c          |   2 +
>  fs/xfs/xfs_trace.h          |  97 ++++
>  fs/xfs/xfs_zone_alloc.c     | 959 ++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_zone_alloc.h     |  34 ++
>  fs/xfs/xfs_zone_priv.h      |  89 ++++
>  12 files changed, 1238 insertions(+), 10 deletions(-)
>  create mode 100644 fs/xfs/xfs_zone_alloc.c
>  create mode 100644 fs/xfs/xfs_zone_alloc.h
>  create mode 100644 fs/xfs/xfs_zone_priv.h
> 
> diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
> index ea8e66c1e969..28bd2627e9ef 100644
> --- a/fs/xfs/Makefile
> +++ b/fs/xfs/Makefile
> @@ -137,7 +137,8 @@ xfs-$(CONFIG_XFS_QUOTA)		+= xfs_dquot.o \
>  				   xfs_quotaops.o
>  
>  # xfs_rtbitmap is shared with libxfs
> -xfs-$(CONFIG_XFS_RT)		+= xfs_rtalloc.o
> +xfs-$(CONFIG_XFS_RT)		+= xfs_rtalloc.o \
> +				   xfs_zone_alloc.o
>  
>  xfs-$(CONFIG_XFS_POSIX_ACL)	+= xfs_acl.o
>  xfs-$(CONFIG_SYSCTL)		+= xfs_sysctl.o
> diff --git a/fs/xfs/libxfs/xfs_rtgroup.h b/fs/xfs/libxfs/xfs_rtgroup.h
> index e35d1d798327..5d8777f819f4 100644
> --- a/fs/xfs/libxfs/xfs_rtgroup.h
> +++ b/fs/xfs/libxfs/xfs_rtgroup.h
> @@ -37,15 +37,27 @@ struct xfs_rtgroup {
>  	xfs_rtxnum_t		rtg_extents;
>  
>  	/*
> -	 * Cache of rt summary level per bitmap block with the invariant that
> -	 * rtg_rsum_cache[bbno] > the maximum i for which rsum[i][bbno] != 0,
> -	 * or 0 if rsum[i][bbno] == 0 for all i.
> -	 *
> +	 * For bitmap based RT devices this points to a cache of rt summary
> +	 * level per bitmap block with the invariant that rtg_rsum_cache[bbno]
> +	 * > the maximum i for which rsum[i][bbno] != 0, or 0 if
> +	 * rsum[i][bbno] == 0 for all i.
>  	 * Reads and writes are serialized by the rsumip inode lock.
> +	 *
> +	 * For zoned RT devices this points to the open zone structure for
> +	 * a group that is open for writers, or is NULL.
>  	 */
> -	uint8_t			*rtg_rsum_cache;
> +	union {
> +		uint8_t			*rtg_rsum_cache;
> +		struct xfs_open_zone	*rtg_open_zone;
> +	};
>  };
>  
> +/*
> + * For zoned RT devices this is set on groups that have no written blocks
> + * and can be picked by the allocator for opening.
> + */
> +#define XFS_RTG_FREE			XA_MARK_0
> +
>  static inline struct xfs_rtgroup *to_rtg(struct xfs_group *xg)
>  {
>  	return container_of(xg, struct xfs_rtgroup, rtg_group);
> diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h
> index 76f3c31573ec..f6f4f2d4b5db 100644
> --- a/fs/xfs/libxfs/xfs_types.h
> +++ b/fs/xfs/libxfs/xfs_types.h
> @@ -243,12 +243,23 @@ enum xfs_free_counter {
>  	 * Number of free RT extents on the RT device.
>  	 */
>  	XC_FREE_RTEXTENTS,
> +
> +	/*
> +	 * Number of available for use RT extents.
> +	 *
> +	 * This counter only exists for zoned RT device and indicates the number
> +	 * of RT extents that can be directly used by writes.  XC_FREE_RTEXTENTS
> +	 * also includes blocks that have been written previously and freed, but
> +	 * sit in a rtgroup that still needs a zone reset.
> +	 */
> +	XC_FREE_RTAVAILABLE,
>  	XC_FREE_NR,
>  };
>  
>  #define XFS_FREECOUNTER_STR \
>  	{ XC_FREE_BLOCKS,		"blocks" }, \
> -	{ XC_FREE_RTEXTENTS,		"rtextents" }
> +	{ XC_FREE_RTEXTENTS,		"rtextents" }, \
> +	{ XC_FREE_RTAVAILABLE,		"rtavailable" }
>  
>  /*
>   * Type verifier functions
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index f8851ff835de..6493bdb57351 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -20,6 +20,7 @@
>  #include "xfs_sysfs.h"
>  #include "xfs_sb.h"
>  #include "xfs_health.h"
> +#include "xfs_zone_alloc.h"
>  
>  struct kmem_cache	*xfs_log_ticket_cache;
>  
> @@ -3540,6 +3541,9 @@ xlog_force_shutdown(
>  	spin_unlock(&log->l_icloglock);
>  
>  	wake_up_var(&log->l_opstate);
> +	if (IS_ENABLED(CONFIG_XFS_RT) && xfs_has_zoned(log->l_mp))
> +		xfs_zoned_wake_all(log->l_mp);
> +
>  	return log_error;
>  }
>  
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index b6004e456ed3..06e34c43cc94 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -40,6 +40,7 @@
>  #include "xfs_rtrmap_btree.h"
>  #include "xfs_rtrefcount_btree.h"
>  #include "scrub/stats.h"
> +#include "xfs_zone_alloc.h"
>  
>  static DEFINE_MUTEX(xfs_uuid_table_mutex);
>  static int xfs_uuid_table_size;
> @@ -467,6 +468,7 @@ xfs_mount_reset_sbqflags(
>  static const char *const xfs_free_pool_name[] = {
>  	[XC_FREE_BLOCKS]	= "free blocks",
>  	[XC_FREE_RTEXTENTS]	= "free rt extents",
> +	[XC_FREE_RTAVAILABLE]	= "available rt extents",
>  };
>  
>  uint64_t
> @@ -1045,6 +1047,12 @@ xfs_mountfs(
>  	if (xfs_is_readonly(mp) && !xfs_has_norecovery(mp))
>  		xfs_log_clean(mp);
>  
> +	if (xfs_has_zoned(mp)) {
> +		error = xfs_mount_zones(mp);
> +		if (error)
> +			goto out_rtunmount;
> +	}
> +
>  	/*
>  	 * Complete the quota initialisation, post-log-replay component.
>  	 */
> @@ -1087,6 +1095,8 @@ xfs_mountfs(
>   out_agresv:
>  	xfs_fs_unreserve_ag_blocks(mp);
>  	xfs_qm_unmount_quotas(mp);
> +	if (xfs_has_zoned(mp))
> +		xfs_unmount_zones(mp);
>   out_rtunmount:
>  	xfs_rtunmount_inodes(mp);
>   out_rele_rip:
> @@ -1168,6 +1178,8 @@ xfs_unmountfs(
>  	xfs_blockgc_stop(mp);
>  	xfs_fs_unreserve_ag_blocks(mp);
>  	xfs_qm_unmount_quotas(mp);
> +	if (xfs_has_zoned(mp))
> +		xfs_unmount_zones(mp);
>  	xfs_rtunmount_inodes(mp);
>  	xfs_irele(mp->m_rootip);
>  	if (mp->m_metadirip)
> @@ -1251,7 +1263,7 @@ xfs_freecounter_unavailable(
>  	struct xfs_mount	*mp,
>  	enum xfs_free_counter	ctr)
>  {
> -	if (ctr == XC_FREE_RTEXTENTS)
> +	if (ctr == XC_FREE_RTEXTENTS || ctr == XC_FREE_RTAVAILABLE)
>  		return 0;
>  	return mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
>  }
> @@ -1341,7 +1353,8 @@ xfs_dec_freecounter(
>  
>  		lcounter = (long long)mp->m_resblks[ctr].avail - delta;
>  		if (lcounter < 0) {
> -			xfs_warn_once(mp,
> +			if (ctr == XC_FREE_BLOCKS)
> +				xfs_warn_once(mp,

That probably should go in the patch enabling xfs_dec_freecounter to
take XC_FREE_RTEXTENTS.

>  "Reserve blocks depleted! Consider increasing reserve pool size.");
>  			goto fdblocks_enospc;
>  		}
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 7c29f3f9ba78..a0e51ce5b84c 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -205,6 +205,7 @@ typedef struct xfs_mount {
>  	bool			m_fail_unmount;
>  	bool			m_finobt_nores; /* no per-AG finobt resv. */
>  	bool			m_update_sb;	/* sb needs update in mount */
> +	unsigned int		m_max_open_zones;
>  
>  	/*
>  	 * Bitsets of per-fs metadata that have been checked and/or are sick.
> @@ -257,6 +258,7 @@ typedef struct xfs_mount {
>  		uint64_t	save;		/* reserved blks @ remount,ro */
>  	} m_resblks[XC_FREE_NR];
>  	struct delayed_work	m_reclaim_work;	/* background inode reclaim */
> +	struct xfs_zone_info	*m_zone_info;	/* zone allocator information */
>  	struct dentry		*m_debugfs;	/* debugfs parent */
>  	struct xfs_kobj		m_kobj;
>  	struct xfs_kobj		m_error_kobj;
> diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
> index a0fd1dc5d362..6a45749daf57 100644
> --- a/fs/xfs/xfs_rtalloc.c
> +++ b/fs/xfs/xfs_rtalloc.c
> @@ -33,6 +33,7 @@
>  #include "xfs_trace.h"
>  #include "xfs_rtrefcount_btree.h"
>  #include "xfs_reflink.h"
> +#include "xfs_zone_alloc.h"
>  
>  /*
>   * Return whether there are any free extents in the size range given
> @@ -663,7 +664,8 @@ xfs_rtunmount_rtg(
>  
>  	for (i = 0; i < XFS_RTGI_MAX; i++)
>  		xfs_rtginode_irele(&rtg->rtg_inodes[i]);
> -	kvfree(rtg->rtg_rsum_cache);
> +	if (!xfs_has_zoned(rtg_mount(rtg)))
> +		kvfree(rtg->rtg_rsum_cache);
>  }
>  
>  static int
> @@ -1573,6 +1575,8 @@ xfs_rtmount_rtg(
>  		}
>  	}
>  
> +	if (xfs_has_zoned(mp))
> +		return 0;
>  	return xfs_alloc_rsum_cache(rtg, mp->m_sb.sb_rbmblocks);
>  }
>  
> diff --git a/fs/xfs/xfs_trace.c b/fs/xfs/xfs_trace.c
> index 8f530e69c18a..a60556dbd172 100644
> --- a/fs/xfs/xfs_trace.c
> +++ b/fs/xfs/xfs_trace.c
> @@ -49,6 +49,8 @@
>  #include "xfs_metafile.h"
>  #include "xfs_metadir.h"
>  #include "xfs_rtgroup.h"
> +#include "xfs_zone_alloc.h"
> +#include "xfs_zone_priv.h"
>  
>  /*
>   * We include this last to have the helpers above available for the trace
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index a02129c202b2..d4f012e41564 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -102,6 +102,7 @@ struct xfs_rmap_intent;
>  struct xfs_refcount_intent;
>  struct xfs_metadir_update;
>  struct xfs_rtgroup;
> +struct xfs_open_zone;
>  
>  #define XFS_ATTR_FILTER_FLAGS \
>  	{ XFS_ATTR_ROOT,	"ROOT" }, \
> @@ -265,6 +266,100 @@ DEFINE_GROUP_REF_EVENT(xfs_group_grab);
>  DEFINE_GROUP_REF_EVENT(xfs_group_grab_next_tag);
>  DEFINE_GROUP_REF_EVENT(xfs_group_rele);
>  
> +#ifdef CONFIG_XFS_RT
> +DECLARE_EVENT_CLASS(xfs_zone_class,
> +	TP_PROTO(struct xfs_rtgroup *rtg),
> +	TP_ARGS(rtg),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(xfs_rgnumber_t, rgno)
> +		__field(xfs_rgblock_t, used)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = rtg_mount(rtg)->m_super->s_dev;
> +		__entry->rgno = rtg_rgno(rtg);
> +		__entry->used = rtg_rmap(rtg)->i_used_blocks;
> +	),
> +	TP_printk("dev %d:%d rgno 0x%x used 0x%x",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __entry->rgno,
> +		  __entry->used)
> +);
> +
> +#define DEFINE_ZONE_EVENT(name)				\
> +DEFINE_EVENT(xfs_zone_class, name,			\
> +	TP_PROTO(struct xfs_rtgroup *rtg),		\
> +	TP_ARGS(rtg))
> +DEFINE_ZONE_EVENT(xfs_zone_full);
> +DEFINE_ZONE_EVENT(xfs_zone_activate);
> +
> +TRACE_EVENT(xfs_zone_free_blocks,
> +	TP_PROTO(struct xfs_rtgroup *rtg, xfs_rgblock_t rgbno,
> +		 xfs_extlen_t len),
> +	TP_ARGS(rtg, rgbno, len),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(xfs_rgnumber_t, rgno)
> +		__field(xfs_rgblock_t, used)
> +		__field(xfs_rgblock_t, rgbno)
> +		__field(xfs_extlen_t, len)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = rtg_mount(rtg)->m_super->s_dev;
> +		__entry->rgno = rtg_rgno(rtg);
> +		__entry->used = rtg_rmap(rtg)->i_used_blocks;
> +		__entry->rgbno = rgbno;
> +		__entry->len = len;
> +	),
> +	TP_printk("dev %d:%d rgno 0x%x used 0x%x rgbno 0x%x len 0x%x",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __entry->rgno,
> +		  __entry->used,
> +		  __entry->rgbno,
> +		  __entry->len)
> +);
> +
> +DECLARE_EVENT_CLASS(xfs_zone_alloc_class,
> +	TP_PROTO(struct xfs_open_zone *oz, xfs_rgblock_t rgbno,
> +		 xfs_extlen_t len),
> +	TP_ARGS(oz, rgbno, len),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(xfs_rgnumber_t, rgno)
> +		__field(xfs_rgblock_t, used)
> +		__field(xfs_rgblock_t, written)
> +		__field(xfs_rgblock_t, write_pointer)
> +		__field(xfs_rgblock_t, rgbno)
> +		__field(xfs_extlen_t, len)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = rtg_mount(oz->oz_rtg)->m_super->s_dev;
> +		__entry->rgno = rtg_rgno(oz->oz_rtg);
> +		__entry->used = rtg_rmap(oz->oz_rtg)->i_used_blocks;
> +		__entry->written = oz->oz_written;
> +		__entry->write_pointer = oz->oz_write_pointer;
> +		__entry->rgbno = rgbno;
> +		__entry->len = len;
> +	),
> +	TP_printk("dev %d:%d rgno 0x%x used 0x%x written 0x%x wp 0x%x rgbno 0x%x len 0x%x",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __entry->rgno,
> +		  __entry->used,
> +		  __entry->written,
> +		  __entry->write_pointer,
> +		  __entry->rgbno,
> +		  __entry->len)
> +);
> +
> +#define DEFINE_ZONE_ALLOC_EVENT(name)				\
> +DEFINE_EVENT(xfs_zone_alloc_class, name,			\
> +	TP_PROTO(struct xfs_open_zone *oz, xfs_rgblock_t rgbno,	\
> +		 xfs_extlen_t len),				\
> +	TP_ARGS(oz, rgbno, len))
> +DEFINE_ZONE_ALLOC_EVENT(xfs_zone_record_blocks);
> +DEFINE_ZONE_ALLOC_EVENT(xfs_zone_alloc_blocks);
> +#endif /* CONFIG_XFS_RT */
> +
>  TRACE_EVENT(xfs_inodegc_worker,
>  	TP_PROTO(struct xfs_mount *mp, unsigned int shrinker_hits),
>  	TP_ARGS(mp, shrinker_hits),
> @@ -3982,6 +4077,7 @@ DEFINE_SIMPLE_IO_EVENT(xfs_reflink_cancel_cow_range);
>  DEFINE_SIMPLE_IO_EVENT(xfs_reflink_end_cow);
>  DEFINE_INODE_IREC_EVENT(xfs_reflink_cow_remap_from);
>  DEFINE_INODE_IREC_EVENT(xfs_reflink_cow_remap_to);
> +DEFINE_INODE_IREC_EVENT(xfs_reflink_cow_remap_skip);
>  
>  DEFINE_INODE_ERROR_EVENT(xfs_reflink_cancel_cow_range_error);
>  DEFINE_INODE_ERROR_EVENT(xfs_reflink_end_cow_error);
> @@ -5665,6 +5761,7 @@ TRACE_EVENT(xfs_growfs_check_rtgeom,
>  
>  TRACE_DEFINE_ENUM(XC_FREE_BLOCKS);
>  TRACE_DEFINE_ENUM(XC_FREE_RTEXTENTS);
> +TRACE_DEFINE_ENUM(XC_FREE_RTAVAILABLE);
>  
>  DECLARE_EVENT_CLASS(xfs_freeblocks_class,
>  	TP_PROTO(struct xfs_mount *mp, enum xfs_free_counter ctr,
> diff --git a/fs/xfs/xfs_zone_alloc.c b/fs/xfs/xfs_zone_alloc.c
> new file mode 100644
> index 000000000000..f41a2cc84382
> --- /dev/null
> +++ b/fs/xfs/xfs_zone_alloc.c
> @@ -0,0 +1,959 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2023-2025 Christoph Hellwig.
> + * Copyright (c) 2024-2025, Western Digital Corporation or its affiliates.
> + */
> +#include "xfs.h"
> +#include "xfs_shared.h"
> +#include "xfs_format.h"
> +#include "xfs_log_format.h"
> +#include "xfs_error.h"
> +#include "xfs_trans_resv.h"
> +#include "xfs_mount.h"
> +#include "xfs_inode.h"
> +#include "xfs_iomap.h"
> +#include "xfs_trans.h"
> +#include "xfs_alloc.h"
> +#include "xfs_bmap.h"
> +#include "xfs_bmap_btree.h"
> +#include "xfs_trans_space.h"
> +#include "xfs_refcount.h"
> +#include "xfs_rtbitmap.h"
> +#include "xfs_rtrmap_btree.h"
> +#include "xfs_zone_alloc.h"
> +#include "xfs_zone_priv.h"
> +#include "xfs_zones.h"
> +#include "xfs_trace.h"
> +
> +void
> +xfs_open_zone_put(
> +	struct xfs_open_zone	*oz)
> +{
> +	if (atomic_dec_and_test(&oz->oz_ref)) {
> +		xfs_rtgroup_rele(oz->oz_rtg);
> +		kfree(oz);
> +	}
> +}
> +
> +static void
> +xfs_open_zone_mark_full(
> +	struct xfs_open_zone	*oz)
> +{
> +	struct xfs_rtgroup	*rtg = oz->oz_rtg;
> +	struct xfs_mount	*mp = rtg_mount(rtg);
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +
> +	trace_xfs_zone_full(rtg);
> +
> +	WRITE_ONCE(rtg->rtg_open_zone, NULL);
> +
> +	spin_lock(&zi->zi_open_zones_lock);
> +	if (oz->oz_is_gc) {
> +		ASSERT(current == zi->zi_gc_thread);
> +		zi->zi_open_gc_zone = NULL;
> +	} else {
> +		zi->zi_nr_open_zones--;
> +		list_del_init(&oz->oz_entry);
> +	}
> +	spin_unlock(&zi->zi_open_zones_lock);
> +	xfs_open_zone_put(oz);
> +
> +	wake_up_all(&zi->zi_zone_wait);
> +}
> +
> +static void
> +xfs_zone_record_blocks(
> +	struct xfs_trans	*tp,
> +	xfs_fsblock_t		fsbno,
> +	xfs_filblks_t		len,
> +	struct xfs_open_zone	*oz,
> +	bool			used)
> +{
> +	struct xfs_mount	*mp = tp->t_mountp;
> +	struct xfs_rtgroup	*rtg = oz->oz_rtg;
> +	struct xfs_inode	*rmapip = rtg_rmap(rtg);
> +
> +	trace_xfs_zone_record_blocks(oz, xfs_rtb_to_rgbno(mp, fsbno), len);
> +
> +	xfs_rtgroup_lock(rtg, XFS_RTGLOCK_RMAP);
> +	xfs_rtgroup_trans_join(tp, rtg, XFS_RTGLOCK_RMAP);
> +	if (used) {
> +		rmapip->i_used_blocks += len;
> +		ASSERT(rmapip->i_used_blocks <= rtg_blocks(rtg));
> +	} else {
> +		xfs_add_frextents(mp, len);
> +	}
> +	oz->oz_written += len;
> +	if (oz->oz_written == rtg_blocks(rtg))
> +		xfs_open_zone_mark_full(oz);
> +	xfs_trans_log_inode(tp, rmapip, XFS_ILOG_CORE);
> +}
> +
> +static int
> +xfs_zoned_map_extent(
> +	struct xfs_trans	*tp,
> +	struct xfs_inode	*ip,
> +	struct xfs_bmbt_irec	*new,
> +	struct xfs_open_zone	*oz,
> +	xfs_fsblock_t		old_startblock)
> +{
> +	struct xfs_bmbt_irec	data;
> +	int			nmaps = 1;
> +	int			error;
> +
> +	/* Grab the corresponding mapping in the data fork. */
> +	error = xfs_bmapi_read(ip, new->br_startoff, new->br_blockcount, &data,
> +			       &nmaps, 0);
> +	if (error)
> +		return error;
> +
> +	/*
> +	 * Cap the update to the existing extent in the data fork because we can
> +	 * only overwrite one extent at a time.
> +	 */
> +	ASSERT(new->br_blockcount >= data.br_blockcount);
> +	new->br_blockcount = data.br_blockcount;
> +
> +	/*
> +	 * If a data write raced with this GC write, keep the existing data in
> +	 * the data fork, mark our newly written GC extent as reclaimable, then
> +	 * move on to the next extent.
> +	 */
> +	if (old_startblock != NULLFSBLOCK &&
> +	    old_startblock != data.br_startblock)
> +		goto skip;
> +
> +	trace_xfs_reflink_cow_remap_from(ip, new);
> +	trace_xfs_reflink_cow_remap_to(ip, &data);
> +
> +	error = xfs_iext_count_extend(tp, ip, XFS_DATA_FORK,
> +			XFS_IEXT_REFLINK_END_COW_CNT);
> +	if (error)
> +		return error;
> +
> +	if (data.br_startblock != HOLESTARTBLOCK) {
> +		ASSERT(data.br_startblock != DELAYSTARTBLOCK);
> +		ASSERT(!isnullstartblock(data.br_startblock));
> +
> +		xfs_bmap_unmap_extent(tp, ip, XFS_DATA_FORK, &data);
> +		if (xfs_is_reflink_inode(ip)) {
> +			xfs_refcount_decrease_extent(tp, true, &data);
> +		} else {
> +			error = xfs_free_extent_later(tp, data.br_startblock,
> +					data.br_blockcount, NULL,
> +					XFS_AG_RESV_NONE,
> +					XFS_FREE_EXTENT_REALTIME);
> +			if (error)
> +				return error;
> +		}
> +	}
> +
> +	xfs_zone_record_blocks(tp, new->br_startblock, new->br_blockcount, oz,
> +			true);
> +
> +	/* Map the new blocks into the data fork. */
> +	xfs_bmap_map_extent(tp, ip, XFS_DATA_FORK, new);
> +	return 0;
> +
> +skip:
> +	trace_xfs_reflink_cow_remap_skip(ip, new);
> +	xfs_zone_record_blocks(tp, new->br_startblock, new->br_blockcount, oz,
> +			false);
> +	return 0;
> +}
> +
> +int
> +xfs_zoned_end_io(
> +	struct xfs_inode	*ip,
> +	xfs_off_t		offset,
> +	xfs_off_t		count,
> +	xfs_daddr_t		daddr,
> +	struct xfs_open_zone	*oz,
> +	xfs_fsblock_t		old_startblock)
> +{
> +	struct xfs_mount	*mp = ip->i_mount;
> +	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, offset + count);
> +	struct xfs_bmbt_irec	new = {
> +		.br_startoff	= XFS_B_TO_FSBT(mp, offset),
> +		.br_startblock	= xfs_daddr_to_rtb(mp, daddr),
> +		.br_state	= XFS_EXT_NORM,
> +	};
> +	unsigned int		resblks =
> +		XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> +	struct xfs_trans	*tp;
> +	int			error;
> +
> +	if (xfs_is_shutdown(mp))
> +		return -EIO;
> +
> +	while (new.br_startoff < end_fsb) {
> +		new.br_blockcount = end_fsb - new.br_startoff;
> +
> +		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
> +				XFS_TRANS_RESERVE | XFS_TRANS_RES_FDBLKS, &tp);
> +		if (error)
> +			return error;
> +		xfs_ilock(ip, XFS_ILOCK_EXCL);
> +		xfs_trans_ijoin(tp, ip, 0);
> +
> +		error = xfs_zoned_map_extent(tp, ip, &new, oz, old_startblock);
> +		if (error)
> +			xfs_trans_cancel(tp);
> +		else
> +			error = xfs_trans_commit(tp);
> +		xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +		if (error)
> +			return error;
> +
> +		new.br_startoff += new.br_blockcount;
> +		new.br_startblock += new.br_blockcount;
> +		if (old_startblock != NULLFSBLOCK)
> +			old_startblock += new.br_blockcount;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * "Free" blocks allocated in a zone.
> + *
> + * Just decrement the used blocks counter and report the space as freed.
> + */
> +int
> +xfs_zone_free_blocks(
> +	struct xfs_trans	*tp,
> +	struct xfs_rtgroup	*rtg,
> +	xfs_fsblock_t		fsbno,
> +	xfs_filblks_t		len)
> +{
> +	struct xfs_mount	*mp = tp->t_mountp;
> +	struct xfs_inode	*rmapip = rtg_rmap(rtg);
> +
> +	xfs_assert_ilocked(rmapip, XFS_ILOCK_EXCL);
> +
> +	if (len > rmapip->i_used_blocks) {
> +		xfs_err(mp,
> +"trying to free more blocks (%lld) than used counter (%u).",
> +			len, rmapip->i_used_blocks);
> +		ASSERT(len <= rmapip->i_used_blocks);
> +		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> +		return -EFSCORRUPTED;
> +	}
> +
> +	trace_xfs_zone_free_blocks(rtg, xfs_rtb_to_rgbno(mp, fsbno), len);
> +
> +	rmapip->i_used_blocks -= len;
> +	xfs_add_frextents(mp, len);
> +	xfs_trans_log_inode(tp, rmapip, XFS_ILOG_CORE);
> +	return 0;
> +}
> +
> +/*
> + * Check if the zone containing the data just before the offset we are
> + * writing to is still open and has space.
> + */
> +static struct xfs_open_zone *
> +xfs_last_used_zone(
> +	struct iomap_ioend	*ioend)
> +{
> +	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
> +	struct xfs_mount	*mp = ip->i_mount;
> +	xfs_fileoff_t		offset_fsb = XFS_B_TO_FSB(mp, ioend->io_offset);
> +	struct xfs_rtgroup	*rtg = NULL;
> +	struct xfs_open_zone	*oz = NULL;
> +	struct xfs_iext_cursor	icur;
> +	struct xfs_bmbt_irec	got;
> +
> +	xfs_ilock(ip, XFS_ILOCK_SHARED);
> +	if (!xfs_iext_lookup_extent_before(ip, &ip->i_df, &offset_fsb,
> +				&icur, &got)) {
> +		xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +		return NULL;
> +	}
> +	xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +
> +	rtg = xfs_rtgroup_grab(mp, xfs_rtb_to_rgno(mp, got.br_startblock));
> +	if (!rtg)
> +		return NULL;
> +
> +	xfs_ilock(rtg_rmap(rtg), XFS_ILOCK_SHARED);
> +	oz = READ_ONCE(rtg->rtg_open_zone);
> +	if (oz && (oz->oz_is_gc || !atomic_inc_not_zero(&oz->oz_ref)))
> +		oz = NULL;
> +	xfs_iunlock(rtg_rmap(rtg), XFS_ILOCK_SHARED);
> +
> +	xfs_rtgroup_rele(rtg);
> +	return oz;
> +}
> +
> +static struct xfs_group *
> +xfs_find_free_zone(
> +	struct xfs_mount	*mp,
> +	unsigned long		start,
> +	unsigned long		end)
> +{
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	XA_STATE		(xas, &mp->m_groups[XG_TYPE_RTG].xa, start);
> +	struct xfs_group	*xg;
> +
> +	xas_lock(&xas);
> +	xas_for_each_marked(&xas, xg, end, XFS_RTG_FREE)
> +		if (atomic_inc_not_zero(&xg->xg_active_ref))
> +			goto found;
> +	xas_unlock(&xas);
> +	return NULL;
> +
> +found:
> +	xas_clear_mark(&xas, XFS_RTG_FREE);
> +	atomic_dec(&zi->zi_nr_free_zones);
> +	zi->zi_free_zone_cursor = xg->xg_gno;
> +	xas_unlock(&xas);
> +	return xg;
> +}
> +
> +static struct xfs_open_zone *
> +xfs_init_open_zone(
> +	struct xfs_rtgroup	*rtg,
> +	xfs_rgblock_t		write_pointer,
> +	bool			is_gc)
> +{
> +	struct xfs_open_zone	*oz;
> +
> +	oz = kzalloc(sizeof(*oz), GFP_NOFS | __GFP_NOFAIL);
> +	spin_lock_init(&oz->oz_alloc_lock);
> +	atomic_set(&oz->oz_ref, 1);
> +	oz->oz_rtg = rtg;
> +	oz->oz_write_pointer = write_pointer;
> +	oz->oz_written = write_pointer;
> +	oz->oz_is_gc = is_gc;
> +
> +	/*
> +	 * All dereferences of rtg->rtg_open_zone hold the ILOCK for the rmap
> +	 * inode, but we don't really want to take that here because we are
> +	 * under the zone_list_lock.  Ensure the pointer is only set for a fully
> +	 * initialized open zone structure so that a racy lookup finding it is
> +	 * fine.
> +	 */
> +	WRITE_ONCE(rtg->rtg_open_zone, oz);
> +	return oz;
> +}
> +
> +/*
> + * Find a completely free zone, open it, and return a reference.
> + */
> +struct xfs_open_zone *
> +xfs_open_zone(
> +	struct xfs_mount	*mp,
> +	bool			is_gc)
> +{
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	struct xfs_group	*xg;
> +
> +	xg = xfs_find_free_zone(mp, zi->zi_free_zone_cursor, ULONG_MAX);
> +	if (!xg)
> +		xg = xfs_find_free_zone(mp, 0, zi->zi_free_zone_cursor);
> +	if (!xg)
> +		return NULL;
> +
> +	set_current_state(TASK_RUNNING);
> +	return xfs_init_open_zone(to_rtg(xg), 0, is_gc);
> +}
> +
> +static struct xfs_open_zone *
> +xfs_try_open_zone(
> +	struct xfs_mount	*mp)
> +{
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	struct xfs_open_zone	*oz;
> +
> +	if (zi->zi_nr_open_zones >= mp->m_max_open_zones - XFS_OPEN_GC_ZONES)
> +		return NULL;
> +	if (atomic_read(&zi->zi_nr_free_zones) <
> +	    XFS_GC_ZONES - XFS_OPEN_GC_ZONES)
> +		return NULL;
> +
> +	/*
> +	 * Increment the open zone count to reserve our slot before dropping
> +	 * zi_open_zones_lock.
> +	 */
> +	zi->zi_nr_open_zones++;
> +	spin_unlock(&zi->zi_open_zones_lock);
> +	oz = xfs_open_zone(mp, false);
> +	spin_lock(&zi->zi_open_zones_lock);
> +	if (!oz) {
> +		zi->zi_nr_open_zones--;
> +		return NULL;
> +	}
> +
> +	atomic_inc(&oz->oz_ref);
> +	list_add_tail(&oz->oz_entry, &zi->zi_open_zones);
> +
> +	/*
> +	 * If this was the last free zone, other waiters might be waiting
> +	 * on us to write to it as well.
> +	 */
> +	wake_up_all(&zi->zi_zone_wait);
> +
> +	/* XXX: this is a little verbose, but let's keep it for now */
> +	xfs_info(mp, "using zone %u (%u)",
> +		 rtg_rgno(oz->oz_rtg), zi->zi_nr_open_zones);

Should this XXX become a tracepoint?

> +	trace_xfs_zone_activate(oz->oz_rtg);
> +	return oz;
> +}
> +
> +static bool
> +xfs_try_use_zone(
> +	struct xfs_zone_info	*zi,
> +	struct xfs_open_zone	*oz)
> +{
> +	if (oz->oz_write_pointer == rtg_blocks(oz->oz_rtg))
> +		return false;
> +	if (!atomic_inc_not_zero(&oz->oz_ref))
> +		return false;
> +
> +	/*
> +	 * If we couldn't match by inode or life time we just pick the first
> +	 * zone with enough space above.  For that we want the least busy zone
> +	 * for some definition of "least" busy.  For now this simple LRU
> +	 * algorithm that rotates every zone to the end of the list will do it,
> +	 * even if it isn't exactly cache friendly.
> +	 */
> +	if (!list_is_last(&oz->oz_entry, &zi->zi_open_zones))
> +		list_move_tail(&oz->oz_entry, &zi->zi_open_zones);
> +	return true;
> +}
> +
> +static struct xfs_open_zone *
> +xfs_select_open_zone_lru(
> +	struct xfs_zone_info	*zi)
> +{
> +	struct xfs_open_zone	*oz;
> +
> +	lockdep_assert_held(&zi->zi_open_zones_lock);
> +
> +	list_for_each_entry(oz, &zi->zi_open_zones, oz_entry)
> +		if (xfs_try_use_zone(zi, oz))
> +			return oz;
> +
> +	cond_resched_lock(&zi->zi_open_zones_lock);
> +	return NULL;
> +}
> +
> +static struct xfs_open_zone *
> +xfs_select_open_zone_mru(
> +	struct xfs_zone_info	*zi)
> +{
> +	struct xfs_open_zone	*oz;
> +
> +	lockdep_assert_held(&zi->zi_open_zones_lock);
> +
> +	list_for_each_entry_reverse(oz, &zi->zi_open_zones, oz_entry)
> +		if (xfs_try_use_zone(zi, oz))
> +			return oz;
> +
> +	cond_resched_lock(&zi->zi_open_zones_lock);
> +	return NULL;
> +}
> +
> +/*
> + * Try to pack inodes that are written back after they were closed tight instead
> + * of trying to open new zones for them or spread them to the least recently
> + * used zone.  This optimizes the data layout for workloads that untar or copy
> + * a lot of small files.  Right now this does not separate multiple such
> + * streams.
> + */
> +static inline bool xfs_zoned_pack_tight(struct xfs_inode *ip)
> +{
> +	return !inode_is_open_for_write(VFS_I(ip)) &&
> +		!(ip->i_diflags & XFS_DIFLAG_APPEND);
> +}
> +
> +/*
> + * Pick a new zone for writes.
> + *
> + * If we aren't using up our budget of open zones just open a new one from the
> + * freelist.  Else try to find one that matches the expected data lifetime.  If
> + * we don't find one that is good pick any zone that is available.
> + */
> +static struct xfs_open_zone *
> +xfs_select_zone_nowait(
> +	struct xfs_mount	*mp,
> +	bool			pack_tight)
> +{
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	struct xfs_open_zone	*oz = NULL;
> +
> +	if (xfs_is_shutdown(mp))
> +		return NULL;
> +
> +	spin_lock(&zi->zi_open_zones_lock);
> +	if (pack_tight)
> +		oz = xfs_select_open_zone_mru(zi);
> +	if (oz)
> +		goto out_unlock;
> +
> +	/*
> +	 * See if we can open a new zone and use that.
> +	 */
> +	oz = xfs_try_open_zone(mp);
> +	if (oz)
> +		goto out_unlock;
> +
> +	oz = xfs_select_open_zone_lru(zi);
> +out_unlock:
> +	spin_unlock(&zi->zi_open_zones_lock);
> +	return oz;
> +}
> +
> +static struct xfs_open_zone *
> +xfs_select_zone(
> +	struct xfs_mount	*mp,
> +	bool			pack_tight)
> +{
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	DEFINE_WAIT		(wait);
> +	struct xfs_open_zone	*oz;
> +
> +	oz = xfs_select_zone_nowait(mp, pack_tight);
> +	if (oz)
> +		return oz;
> +
> +	for (;;) {
> +		prepare_to_wait(&zi->zi_zone_wait, &wait, TASK_UNINTERRUPTIBLE);
> +		oz = xfs_select_zone_nowait(mp, pack_tight);
> +		if (oz)
> +			break;
> +		schedule();
> +	}
> +	finish_wait(&zi->zi_zone_wait, &wait);
> +	return oz;
> +}
> +
> +static unsigned int
> +xfs_zone_alloc_blocks(
> +	struct xfs_open_zone	*oz,
> +	xfs_filblks_t		count_fsb,
> +	sector_t		*sector,
> +	bool			*is_seq)
> +{
> +	struct xfs_rtgroup	*rtg = oz->oz_rtg;
> +	struct xfs_mount	*mp = rtg_mount(rtg);
> +	xfs_rgblock_t		rgbno;
> +
> +	spin_lock(&oz->oz_alloc_lock);
> +	count_fsb = min3(count_fsb, XFS_MAX_BMBT_EXTLEN,
> +		(xfs_filblks_t)rtg_blocks(rtg) - oz->oz_write_pointer);
> +	if (!count_fsb) {
> +		spin_unlock(&oz->oz_alloc_lock);
> +		return 0;
> +	}
> +	rgbno = oz->oz_write_pointer;
> +	oz->oz_write_pointer += count_fsb;
> +	spin_unlock(&oz->oz_alloc_lock);
> +
> +	trace_xfs_zone_alloc_blocks(oz, rgbno, count_fsb);
> +
> +	*sector = xfs_gbno_to_daddr(&rtg->rtg_group, 0);
> +	*is_seq = bdev_zone_is_seq(mp->m_rtdev_targp->bt_bdev, *sector);
> +	if (!*is_seq)
> +		*sector += XFS_FSB_TO_BB(mp, rgbno);
> +	return XFS_FSB_TO_B(mp, count_fsb);
> +}
> +
> +void
> +xfs_mark_rtg_boundary(
> +	struct iomap_ioend	*ioend)
> +{
> +	struct xfs_mount	*mp = XFS_I(ioend->io_inode)->i_mount;
> +	sector_t		sector = ioend->io_bio.bi_iter.bi_sector;
> +
> +	if (xfs_rtb_to_rgbno(mp, xfs_daddr_to_rtb(mp, sector)) == 0)
> +		ioend->io_flags |= IOMAP_IOEND_BOUNDARY;
> +}
> +
> +static void
> +xfs_submit_zoned_bio(
> +	struct iomap_ioend	*ioend,
> +	struct xfs_open_zone	*oz,
> +	bool			is_seq)
> +{
> +	ioend->io_bio.bi_iter.bi_sector = ioend->io_sector;
> +	ioend->io_private = oz;
> +	atomic_inc(&oz->oz_ref); /* for xfs_zoned_end_io */
> +
> +	if (is_seq) {
> +		ioend->io_bio.bi_opf &= ~REQ_OP_WRITE;
> +		ioend->io_bio.bi_opf |= REQ_OP_ZONE_APPEND;
> +	} else {
> +		xfs_mark_rtg_boundary(ioend);
> +	}
> +
> +	submit_bio(&ioend->io_bio);
> +}
> +
> +void
> +xfs_zone_alloc_and_submit(
> +	struct iomap_ioend	*ioend,
> +	struct xfs_open_zone	**oz)
> +{
> +	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
> +	struct xfs_mount	*mp = ip->i_mount;
> +	bool			pack_tight = xfs_zoned_pack_tight(ip);
> +	unsigned int		alloc_len;
> +	struct iomap_ioend	*split;
> +	bool			is_seq;
> +
> +	if (xfs_is_shutdown(mp))
> +		goto out_error;
> +
> +	/*
> +	 * If we don't have a cached zone in this write context, see if the
> +	 * last extent before the one we are writing points of an active zone.

"...writing points *to the end* of an active zone" ?

> +	 * If so, just continue writing to it.
> +	 */
> +	if (!*oz && ioend->io_offset)
> +		*oz = xfs_last_used_zone(ioend);

Also, why not return oz instead of passing it out via double pointer?

> +	if (!*oz) {
> +select_zone:
> +		*oz = xfs_select_zone(mp, pack_tight);
> +		if (!*oz)
> +			goto out_error;
> +	}
> +
> +	alloc_len = xfs_zone_alloc_blocks(*oz, XFS_B_TO_FSB(mp, ioend->io_size),
> +			&ioend->io_sector, &is_seq);
> +	if (!alloc_len) {
> +		xfs_open_zone_put(*oz);
> +		goto select_zone;
> +	}
> +
> +	while ((split = iomap_split_ioend(ioend, alloc_len, is_seq))) {
> +		if (IS_ERR(split))
> +			goto out_split_error;
> +		alloc_len -= split->io_bio.bi_iter.bi_size;
> +		xfs_submit_zoned_bio(split, *oz, is_seq);
> +		if (!alloc_len) {
> +			xfs_open_zone_put(*oz);
> +			goto select_zone;
> +		}
> +	}
> +
> +	xfs_submit_zoned_bio(ioend, *oz, is_seq);
> +	return;
> +
> +out_split_error:
> +	ioend->io_bio.bi_status = errno_to_blk_status(PTR_ERR(split));
> +out_error:
> +	bio_io_error(&ioend->io_bio);
> +}
> +
> +void
> +xfs_zoned_wake_all(
> +	struct xfs_mount	*mp)
> +{
> +	if (!(mp->m_super->s_flags & SB_ACTIVE))
> +		return; /* can happen during log recovery */
> +	wake_up_all(&mp->m_zone_info->zi_zone_wait);
> +}
> +
> +/*
> + * Check if @rgbno in @rgb is a potentially valid block.  It might still be
> + * unused, but that information is only found in the rmap.
> + */
> +bool
> +xfs_zone_rgbno_is_valid(
> +	struct xfs_rtgroup	*rtg,
> +	xfs_rgnumber_t		rgbno)
> +{
> +	lockdep_assert_held(&rtg_rmap(rtg)->i_lock);
> +
> +	if (rtg->rtg_open_zone)
> +		return rgbno < rtg->rtg_open_zone->oz_write_pointer;
> +	return !xa_get_mark(&rtg_mount(rtg)->m_groups[XG_TYPE_RTG].xa,
> +			rtg_rgno(rtg), XFS_RTG_FREE);
> +}
> +
> +static void
> +xfs_free_open_zones(
> +	struct xfs_zone_info	*zi)
> +{
> +	struct xfs_open_zone	*oz;
> +
> +	spin_lock(&zi->zi_open_zones_lock);
> +	while ((oz = list_first_entry_or_null(&zi->zi_open_zones,
> +			struct xfs_open_zone, oz_entry))) {
> +		list_del(&oz->oz_entry);
> +		xfs_open_zone_put(oz);
> +	}
> +	spin_unlock(&zi->zi_open_zones_lock);
> +}
> +
> +struct xfs_init_zones {
> +	struct xfs_mount	*mp;
> +	uint64_t		available;
> +	uint64_t		reclaimable;
> +};
> +
> +static int
> +xfs_init_zone(
> +	struct xfs_init_zones	*iz,
> +	struct xfs_rtgroup	*rtg,
> +	struct blk_zone		*zone)
> +{
> +	struct xfs_mount	*mp = rtg_mount(rtg);
> +	struct xfs_zone_info	*zi = mp->m_zone_info;
> +	uint64_t		used = rtg_rmap(rtg)->i_used_blocks;
> +	xfs_rgblock_t		write_pointer, highest_rgbno;
> +
> +	if (zone && !xfs_zone_validate(zone, rtg, &write_pointer))
> +		return -EFSCORRUPTED;
> +
> +	/*
> +	 * For sequential write required zones we retrieved the hardware write
> +	 * pointer above.
> +	 *
> +	 * For conventional zones or conventional devices we don't have that
> +	 * luxury.  Instead query the rmap to find the highest recorded block
> +	 * and set the write pointer to the block after that.  In case of a
> +	 * power loss this misses blocks where the data I/O has completed but
> +	 * not recorded in the rmap yet, and it also rewrites blocks if the most
> +	 * recently written ones got deleted again before unmount, but this is
> +	 * the best we can do without hardware support.
> +	 */
> +	if (!zone || zone->cond == BLK_ZONE_COND_NOT_WP) {
> +		xfs_rtgroup_lock(rtg, XFS_RTGLOCK_RMAP);
> +		highest_rgbno = xfs_rtrmap_highest_rgbno(rtg);
> +		if (highest_rgbno == NULLRGBLOCK)
> +			write_pointer = 0;
> +		else
> +			write_pointer = highest_rgbno + 1;
> +		xfs_rtgroup_unlock(rtg, XFS_RTGLOCK_RMAP);
> +	}
> +
> +	if (write_pointer == 0) {
> +		/* zone is empty */
> +		atomic_inc(&zi->zi_nr_free_zones);
> +		xfs_group_set_mark(&rtg->rtg_group, XFS_RTG_FREE);
> +		iz->available += rtg_blocks(rtg);
> +	} else if (write_pointer < rtg_blocks(rtg)) {
> +		/* zone is open */
> +		struct xfs_open_zone *oz;
> +
> +		atomic_inc(&rtg_group(rtg)->xg_active_ref);
> +		oz = xfs_init_open_zone(rtg, write_pointer, false);
> +		list_add_tail(&oz->oz_entry, &zi->zi_open_zones);
> +		zi->zi_nr_open_zones++;
> +
> +		iz->available += (rtg_blocks(rtg) - write_pointer);
> +		iz->reclaimable += write_pointer - used;
> +	} else if (used < rtg_blocks(rtg)) {
> +		/* zone fully written, but has freed blocks */
> +		iz->reclaimable += (rtg_blocks(rtg) - used);
> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +xfs_get_zone_info_cb(
> +	struct blk_zone		*zone,
> +	unsigned int		idx,
> +	void			*data)
> +{
> +	struct xfs_init_zones	*iz = data;
> +	struct xfs_mount	*mp = iz->mp;
> +	xfs_fsblock_t		zsbno = xfs_daddr_to_rtb(mp, zone->start);
> +	xfs_rgnumber_t		rgno;
> +	struct xfs_rtgroup	*rtg;
> +	int			error;
> +
> +	if (xfs_rtb_to_rgbno(mp, zsbno) != 0) {
> +		xfs_warn(mp, "mismatched zone start 0x%llx.", zsbno);
> +		return -EFSCORRUPTED;
> +	}
> +
> +	rgno = xfs_rtb_to_rgno(mp, zsbno);
> +	rtg = xfs_rtgroup_grab(mp, rgno);
> +	if (!rtg) {
> +		xfs_warn(mp, "realtime group not found for zone %u.", rgno);
> +		return -EFSCORRUPTED;
> +	}
> +	error = xfs_init_zone(iz, rtg, zone);
> +	xfs_rtgroup_rele(rtg);
> +	return error;
> +}
> +
> +/*
> + * Calculate the max open zone limit based on the of number of
> + * backing zones available
> + */
> +static inline uint32_t
> +xfs_max_open_zones(
> +	struct xfs_mount	*mp)
> +{
> +	unsigned int		max_open, max_open_data_zones;
> +	/*
> +	 * We need two zones for every open data zone,
> +	 * one in reserve as we don't reclaim open zones. One data zone
> +	 * and its spare is included in XFS_MIN_ZONES.
> +	 */
> +	max_open_data_zones = (mp->m_sb.sb_rgcount - XFS_MIN_ZONES) / 2 + 1;
> +	max_open = max_open_data_zones + XFS_OPEN_GC_ZONES;
> +
> +	/*
> +	 * Cap the max open limit to 1/4 of available space
> +	 */
> +	max_open = min(max_open, mp->m_sb.sb_rgcount / 4);
> +
> +	return max(XFS_MIN_OPEN_ZONES, max_open);
> +}
> +
> +/*
> + * Normally we use the open zone limit that the device reports.  If there is
> + * none let the user pick one from the command line.
> + *
> + * If the device doesn't report an open zone limit and there is no override,
> + * allow to hold about a quarter of the zones open.  In theory we could allow
> + * all to be open, but at that point we run into GC deadlocks because we can't
> + * reclaim open zones.
> + *
> + * When used on conventional SSDs a lower open limit is advisable as we'll
> + * otherwise overwhelm the FTL just as much as a conventional block allocator.
> + *
> + * Note: To debug the open zone management code, force max_open to 1 here.
> + */
> +static int
> +xfs_calc_open_zones(
> +	struct xfs_mount	*mp)
> +{
> +	struct block_device	*bdev = mp->m_rtdev_targp->bt_bdev;
> +	unsigned int		bdev_open_zones = bdev_max_open_zones(bdev);
> +
> +	if (!mp->m_max_open_zones) {
> +		if (bdev_open_zones)
> +			mp->m_max_open_zones = bdev_open_zones;
> +		else
> +			mp->m_max_open_zones = xfs_max_open_zones(mp);
> +	}
> +
> +	if (mp->m_max_open_zones < XFS_MIN_OPEN_ZONES) {
> +		xfs_notice(mp, "need at least %u open zones.",
> +			XFS_MIN_OPEN_ZONES);
> +		return -EIO;
> +	}
> +
> +	if (bdev_open_zones && bdev_open_zones < mp->m_max_open_zones) {
> +		mp->m_max_open_zones = bdev_open_zones;
> +		xfs_info(mp, "limiting open zones to %u due to hardware limit.\n",
> +			bdev_open_zones);
> +	}
> +
> +	if (mp->m_max_open_zones > xfs_max_open_zones(mp)) {
> +		mp->m_max_open_zones = xfs_max_open_zones(mp);
> +		xfs_info(mp,
> +"limiting open zones to %u due to total zone count (%u)",
> +			mp->m_max_open_zones, mp->m_sb.sb_rgcount);
> +	}
> +
> +	return 0;
> +}
> +
> +static struct xfs_zone_info *
> +xfs_alloc_zone_info(
> +	struct xfs_mount	*mp)
> +{
> +	struct xfs_zone_info	*zi;
> +
> +	zi = kzalloc(sizeof(*zi), GFP_KERNEL);
> +	if (!zi)
> +		return NULL;
> +	INIT_LIST_HEAD(&zi->zi_open_zones);
> +	INIT_LIST_HEAD(&zi->zi_reclaim_reservations);
> +	spin_lock_init(&zi->zi_reset_list_lock);
> +	spin_lock_init(&zi->zi_open_zones_lock);
> +	spin_lock_init(&zi->zi_reservation_lock);
> +	init_waitqueue_head(&zi->zi_zone_wait);
> +	return zi;
> +}
> +
> +static void
> +xfs_free_zone_info(
> +	struct xfs_zone_info	*zi)
> +{
> +	xfs_free_open_zones(zi);
> +	kfree(zi);
> +}
> +
> +int
> +xfs_mount_zones(
> +	struct xfs_mount	*mp)
> +{
> +	struct xfs_init_zones	iz = {
> +		.mp		= mp,
> +	};
> +	struct xfs_buftarg	*bt = mp->m_rtdev_targp;
> +	int			error;
> +
> +	if (!bt) {
> +		xfs_notice(mp, "RT device missing.");
> +		return -EINVAL;
> +	}
> +
> +	if (!xfs_has_rtgroups(mp) || !xfs_has_rmapbt(mp)) {
> +		xfs_notice(mp, "invalid flag combination.");
> +		return -EFSCORRUPTED;
> +	}
> +	if (mp->m_sb.sb_rextsize != 1) {
> +		xfs_notice(mp, "zoned file systems do not support rextsize.");
> +		return -EFSCORRUPTED;
> +	}
> +	if (mp->m_sb.sb_rgcount < XFS_MIN_ZONES) {
> +		xfs_notice(mp,
> +"zoned file systems need to have at least %u zones.", XFS_MIN_ZONES);
> +		return -EFSCORRUPTED;
> +	}
> +
> +	error = xfs_calc_open_zones(mp);
> +	if (error)
> +		return error;
> +
> +	mp->m_zone_info = xfs_alloc_zone_info(mp);
> +	if (!mp->m_zone_info)
> +		return -ENOMEM;
> +
> +	xfs_info(mp, "%u zones of %u blocks size (%u max open)",
> +		 mp->m_sb.sb_rgcount, mp->m_groups[XG_TYPE_RTG].blocks,
> +		 mp->m_max_open_zones);

Tracepoint?

> +	if (bdev_is_zoned(bt->bt_bdev)) {
> +		error = blkdev_report_zones(bt->bt_bdev,
> +				XFS_FSB_TO_BB(mp, mp->m_sb.sb_rtstart),
> +				mp->m_sb.sb_rgcount, xfs_get_zone_info_cb, &iz);
> +		if (error < 0)
> +			goto out_free_zone_info;
> +	} else {
> +		struct xfs_rtgroup	*rtg = NULL;
> +
> +		while ((rtg = xfs_rtgroup_next(mp, rtg))) {
> +			error = xfs_init_zone(&iz, rtg, NULL);
> +			if (error)
> +				goto out_free_zone_info;
> +		}
> +	}
> +
> +	xfs_set_freecounter(mp, XC_FREE_RTAVAILABLE, iz.available);
> +	xfs_set_freecounter(mp, XC_FREE_RTEXTENTS,
> +		iz.available + iz.reclaimable);

More indenting needed here.

> +	return 0;
> +
> +out_free_zone_info:
> +	xfs_free_zone_info(mp->m_zone_info);
> +	return error;
> +}
> +
> +void
> +xfs_unmount_zones(
> +	struct xfs_mount	*mp)
> +{
> +	xfs_free_zone_info(mp->m_zone_info);
> +}
> diff --git a/fs/xfs/xfs_zone_alloc.h b/fs/xfs/xfs_zone_alloc.h
> new file mode 100644
> index 000000000000..78cd7bfc6ac8
> --- /dev/null
> +++ b/fs/xfs/xfs_zone_alloc.h
> @@ -0,0 +1,34 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _XFS_ZONE_ALLOC_H
> +#define _XFS_ZONE_ALLOC_H
> +
> +struct iomap_ioend;
> +struct xfs_open_zone;
> +
> +void xfs_zone_alloc_and_submit(struct iomap_ioend *ioend,
> +		struct xfs_open_zone **oz);
> +int xfs_zone_free_blocks(struct xfs_trans *tp, struct xfs_rtgroup *rtg,
> +		xfs_fsblock_t fsbno, xfs_filblks_t len);
> +int xfs_zoned_end_io(struct xfs_inode *ip, xfs_off_t offset, xfs_off_t count,
> +		xfs_daddr_t daddr, struct xfs_open_zone *oz,
> +		xfs_fsblock_t old_startblock);
> +void xfs_open_zone_put(struct xfs_open_zone *oz);
> +
> +void xfs_zoned_wake_all(struct xfs_mount *mp);
> +bool xfs_zone_rgbno_is_valid(struct xfs_rtgroup *rtg, xfs_rgnumber_t rgbno);
> +void xfs_mark_rtg_boundary(struct iomap_ioend *ioend);
> +
> +#ifdef CONFIG_XFS_RT
> +int xfs_mount_zones(struct xfs_mount *mp);
> +void xfs_unmount_zones(struct xfs_mount *mp);
> +#else
> +static inline int xfs_mount_zones(struct xfs_mount *mp)
> +{
> +	return -EIO;
> +}
> +static inline void xfs_unmount_zones(struct xfs_mount *mp)
> +{
> +}
> +#endif /* CONFIG_XFS_RT */
> +
> +#endif /* _XFS_ZONE_ALLOC_H */
> diff --git a/fs/xfs/xfs_zone_priv.h b/fs/xfs/xfs_zone_priv.h
> new file mode 100644
> index 000000000000..23d2fd6088ae
> --- /dev/null
> +++ b/fs/xfs/xfs_zone_priv.h
> @@ -0,0 +1,89 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _XFS_ZONE_PRIV_H
> +#define _XFS_ZONE_PRIV_H
> +
> +struct xfs_open_zone {
> +	/*
> +	 * Entry in the open zone list and refcount.  Protected by
> +	 * zi_open_zones_lock in struct xfs_zone_info.
> +	 */
> +	struct list_head	oz_entry;
> +	atomic_t		oz_ref;
> +
> +	/*
> +	 * oz_write_pointer is the write pointer at which space is handed out
> +	 * for conventional zones, or simple the count of blocks handed out
> +	 * so far for sequential write required zones and is protected by
> +	 * oz_alloc_lock/
> +	 */
> +	spinlock_t		oz_alloc_lock;
> +	xfs_rgblock_t		oz_write_pointer;
> +
> +	/*
> +	 * oz_written is the number of blocks for which we've received a
> +	 * write completion.  oz_written must always be <= oz_write_pointer
> +	 * and is protected by the ILOCK of the rmap inode.
> +	 */
> +	xfs_rgblock_t		oz_written;
> +
> +	/*
> +	 * Is this open zone used for garbage collection?  There can only be a
> +	 * single open GC zone, which is pointed to by zi_open_gc_zone in
> +	 * struct xfs_zone_info.  Constant over the life time of an open zone.
> +	 */
> +	bool			oz_is_gc;
> +
> +	/*
> +	 * Pointer to the RT groups structure for this open zone.  Constant over
> +	 * the life time of an open zone.
> +	 */
> +	struct xfs_rtgroup	*oz_rtg;
> +};
> +
> +struct xfs_zone_info {
> +	/*
> +	 * List of pending space reservations:
> +	 */
> +	spinlock_t		zi_reservation_lock;
> +	struct list_head	zi_reclaim_reservations;
> +
> +	/*
> +	 * List and number of open zones:
> +	 */
> +	spinlock_t		zi_open_zones_lock;
> +	struct list_head	zi_open_zones;
> +	unsigned int		zi_nr_open_zones;
> +
> +	/*
> +	 * Free zone search cursor and number of free zones:
> +	 */
> +	unsigned long		zi_free_zone_cursor;
> +	atomic_t		zi_nr_free_zones;
> +
> +	/*
> +	 * Wait queue to wait for free zones or open zone resources to become
> +	 * available:
> +	 */
> +	wait_queue_head_t	zi_zone_wait;
> +
> +	/*
> +	 * Pointer to the GC thread, and the current open zone used by GC
> +	 * (if any).
> +	 *
> +	 * zi_open_gc_zone is mostly private to the GC thread, but can be read
> +	 * for debugging from other threads, in which case zi_open_zones_lock
> +	 * must be taken to access it.
> +	 */
> +	struct task_struct      *zi_gc_thread;
> +	struct xfs_open_zone	*zi_open_gc_zone;
> +
> +	/*
> +	 * List of zones that need a reset:
> +	 */
> +	spinlock_t		zi_reset_list_lock;
> +	struct xfs_group	*zi_reset_list;
> +};
> +
> +struct xfs_open_zone *xfs_open_zone(struct xfs_mount *mp, bool is_gc);
> +
> +#endif /* _XFS_ZONE_PRIV_H */
> -- 
> 2.45.2
> 
>