Re: [PATCH 23/43] xfs: add support for zoned space reservations

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

On Thu, Feb 06, 2025 at 07:44:39AM +0100, Christoph Hellwig wrote:
> For zoned file systems garbage collection (GC) has to take the iolock
> and mmaplock after moving data to a new place to synchronize with
> readers.  This means waiting for garbage collection with the iolock can
> deadlock.
> 
> To avoid this, the worst case required blocks have to be reserved before
> taking the iolock, which is done using a new RTAVAILABLE counter that
> tracks blocks that are free to write into and don't require garbage

Wasn't that in the last patch?  Should this sentence move there?

> collection.  The new helpers try to take these available blocks, and
> if there aren't enough available it wakes and waits for GC.  This is
> done using a list of on-stack reservations to ensure fairness.
> 
> 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_bmap.c     |  15 ++-
>  fs/xfs/xfs_mount.c           |  35 ++---
>  fs/xfs/xfs_zone_alloc.h      |  27 ++++
>  fs/xfs/xfs_zone_priv.h       |   2 +
>  fs/xfs/xfs_zone_space_resv.c | 244 +++++++++++++++++++++++++++++++++++
>  6 files changed, 306 insertions(+), 20 deletions(-)
>  create mode 100644 fs/xfs/xfs_zone_space_resv.c
> 
> diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
> index 28bd2627e9ef..bdedf4bdb1db 100644
> --- a/fs/xfs/Makefile
> +++ b/fs/xfs/Makefile
> @@ -138,7 +138,8 @@ xfs-$(CONFIG_XFS_QUOTA)		+= xfs_dquot.o \
>  
>  # xfs_rtbitmap is shared with libxfs
>  xfs-$(CONFIG_XFS_RT)		+= xfs_rtalloc.o \
> -				   xfs_zone_alloc.o
> +				   xfs_zone_alloc.o \
> +				   xfs_zone_space_resv.o
>  
>  xfs-$(CONFIG_XFS_POSIX_ACL)	+= xfs_acl.o
>  xfs-$(CONFIG_SYSCTL)		+= xfs_sysctl.o
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 522c126e52fb..63255820b58a 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -40,6 +40,7 @@
>  #include "xfs_symlink_remote.h"
>  #include "xfs_inode_util.h"
>  #include "xfs_rtgroup.h"
> +#include "xfs_zone_alloc.h"
>  
>  struct kmem_cache		*xfs_bmap_intent_cache;
>  
> @@ -4788,12 +4789,18 @@ xfs_bmap_del_extent_delay(
>  	da_diff = da_old - da_new;
>  	fdblocks = da_diff;
>  
> -	if (bflags & XFS_BMAPI_REMAP)
> +	if (bflags & XFS_BMAPI_REMAP) {
>  		;
> -	else if (isrt)
> -		xfs_add_frextents(mp, xfs_blen_to_rtbxlen(mp, del->br_blockcount));
> -	else
> +	} else if (isrt) {
> +		xfs_rtbxlen_t	rtxlen;
> +
> +		rtxlen = xfs_blen_to_rtbxlen(mp, del->br_blockcount);
> +		if (xfs_is_zoned_inode(ip))
> +			xfs_zoned_add_available(mp, rtxlen);
> +		xfs_add_frextents(mp, rtxlen);
> +	} else {
>  		fdblocks += del->br_blockcount;
> +	}
>  
>  	xfs_add_fdblocks(mp, fdblocks);
>  	xfs_mod_delalloc(ip, -(int64_t)del->br_blockcount, -da_diff);
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 06e34c43cc94..2b8b392a7336 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -476,22 +476,27 @@ xfs_default_resblks(
>  	struct xfs_mount	*mp,
>  	enum xfs_free_counter	ctr)
>  {
> -	uint64_t resblks;
> -
> -	if (ctr == XC_FREE_RTEXTENTS)
> +	switch (ctr) {
> +	case XC_FREE_BLOCKS:
> +		/*
> +		 * Default to 5% or 8192 FSBs of space reserved, whichever is
> +		 * smaller.
> +		 *
> +		 * This is intended to cover concurrent allocation transactions
> +		 * when we initially hit ENOSPC.  These each require a 4 block
> +		 * reservation. Hence by default we cover roughly 2000
> +		 * concurrent allocation reservations.
> +		 */
> +		return min(div_u64(mp->m_sb.sb_dblocks, 20), 8192ULL);
> +	case XC_FREE_RTEXTENTS:
> +	case XC_FREE_RTAVAILABLE:
> +		if (IS_ENABLED(CONFIG_XFS_RT) && xfs_has_zoned(mp))
> +			return xfs_zoned_default_resblks(mp, ctr);
>  		return 0;
> -
> -	/*
> -	 * We default to 5% or 8192 fsbs of space reserved, whichever is
> -	 * smaller.  This is intended to cover concurrent allocation
> -	 * transactions when we initially hit enospc. These each require a 4
> -	 * block reservation. Hence by default we cover roughly 2000 concurrent
> -	 * allocation reservations.
> -	 */
> -	resblks = mp->m_sb.sb_dblocks;
> -	do_div(resblks, 20);
> -	resblks = min_t(uint64_t, resblks, 8192);
> -	return resblks;
> +	default:
> +		ASSERT(0);
> +		return 0;
> +	}
>  }
>  
>  /* Ensure the summary counts are correct. */
> diff --git a/fs/xfs/xfs_zone_alloc.h b/fs/xfs/xfs_zone_alloc.h
> index 78cd7bfc6ac8..28c9cffb72d5 100644
> --- a/fs/xfs/xfs_zone_alloc.h
> +++ b/fs/xfs/xfs_zone_alloc.h
> @@ -5,6 +5,30 @@
>  struct iomap_ioend;
>  struct xfs_open_zone;
>  
> +struct xfs_zone_alloc_ctx {
> +	struct xfs_open_zone	*open_zone;
> +	xfs_filblks_t		reserved_blocks;
> +};
> +
> +/*
> + * Grab any available space, even if it is less than what the caller asked for.
> + */
> +#define XFS_ZR_GREEDY		(1U << 0)
> +/*
> + * Only grab instantly available space, don't wait or GC.
> + */
> +#define XFS_ZR_NOWAIT		(1U << 1)
> +/*
> + * Dip into the reserved pool.
> + */
> +#define XFS_ZR_RESERVED		(1U << 2)
> +
> +int xfs_zoned_space_reserve(struct xfs_inode *ip, xfs_filblks_t count_fsb,
> +		unsigned int flags, struct xfs_zone_alloc_ctx *ac);
> +void xfs_zoned_space_unreserve(struct xfs_inode *ip,
> +		struct xfs_zone_alloc_ctx *ac);
> +void xfs_zoned_add_available(struct xfs_mount *mp, xfs_filblks_t count_fsb);
> +
>  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,
> @@ -18,6 +42,9 @@ 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);
>  
> +uint64_t xfs_zoned_default_resblks(struct xfs_mount *mp,
> +		enum xfs_free_counter ctr);
> +
>  #ifdef CONFIG_XFS_RT
>  int xfs_mount_zones(struct xfs_mount *mp);
>  void xfs_unmount_zones(struct xfs_mount *mp);
> diff --git a/fs/xfs/xfs_zone_priv.h b/fs/xfs/xfs_zone_priv.h
> index 23d2fd6088ae..5283d77482d4 100644
> --- a/fs/xfs/xfs_zone_priv.h
> +++ b/fs/xfs/xfs_zone_priv.h
> @@ -86,4 +86,6 @@ struct xfs_zone_info {
>  
>  struct xfs_open_zone *xfs_open_zone(struct xfs_mount *mp, bool is_gc);
>  
> +void xfs_zoned_resv_wake_all(struct xfs_mount *mp);
> +
>  #endif /* _XFS_ZONE_PRIV_H */
> diff --git a/fs/xfs/xfs_zone_space_resv.c b/fs/xfs/xfs_zone_space_resv.c
> new file mode 100644
> index 000000000000..eff9be026425
> --- /dev/null
> +++ b/fs/xfs/xfs_zone_space_resv.c
> @@ -0,0 +1,244 @@
> +// 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_trans_resv.h"
> +#include "xfs_mount.h"
> +#include "xfs_inode.h"
> +#include "xfs_rtbitmap.h"
> +#include "xfs_zone_alloc.h"
> +#include "xfs_zone_priv.h"
> +#include "xfs_zones.h"
> +
> +/*
> + * Note: the zoned allocator does not support a rtextsize > 1, so this code and
> + * the allocator itself uses file system blocks interchangeable with realtime
> + * extents without doing the otherwise required conversions.
> + */
> +
> +/*
> + * Per-task space reservation.
> + *
> + * Tasks that need to wait for GC to free up space allocate one of these
> + * on-stack and adds it to the per-mount zi_reclaim_reservations lists.
> + * The GC thread will then wake the tasks in order when space becomes available.
> + */
> +struct xfs_zone_reservation {
> +	struct list_head	entry;
> +	struct task_struct	*task;
> +	xfs_filblks_t		count_fsb;
> +};
> +
> +/*
> + * Calculate the number of reserved blocks.
> + *
> + * XC_FREE_RTEXTENTS counts the user available capacity, to which the file
> + * system can be filled, while XC_FREE_RTAVAILABLE counts the blocks instantly
> + * available for writes without waiting for GC.
> + *
> + * For XC_FREE_RTAVAILABLE only the smaller reservation required for GC and
> + * block zeroing is excluded from the user capacity, while XC_FREE_RTEXTENTS
> + * is further restricted by at least one zone as well as the optional
> + * persistently reserved blocks.  This allows the allocator to run more
> + * smoothly by not always triggering GC.
> + */
> +uint64_t
> +xfs_zoned_default_resblks(
> +	struct xfs_mount	*mp,
> +	enum xfs_free_counter	ctr)
> +{
> +	switch (ctr) {
> +	case XC_FREE_RTEXTENTS:
> +		return (uint64_t)XFS_RESERVED_ZONES *
> +			mp->m_groups[XG_TYPE_RTG].blocks +
> +			mp->m_sb.sb_rtreserved;
> +	case XC_FREE_RTAVAILABLE:
> +		return (uint64_t)XFS_GC_ZONES *
> +			mp->m_groups[XG_TYPE_RTG].blocks;
> +	default:
> +		ASSERT(0);
> +		return 0;
> +	}
> +}
> +
> +void
> +xfs_zoned_resv_wake_all(
> +	struct xfs_mount		*mp)
> +{
> +	struct xfs_zone_info		*zi = mp->m_zone_info;
> +	struct xfs_zone_reservation	*reservation;
> +
> +	spin_lock(&zi->zi_reservation_lock);
> +	list_for_each_entry(reservation, &zi->zi_reclaim_reservations, entry)
> +		wake_up_process(reservation->task);
> +	spin_unlock(&zi->zi_reservation_lock);
> +}
> +
> +void
> +xfs_zoned_add_available(
> +	struct xfs_mount		*mp,
> +	xfs_filblks_t			count_fsb)
> +{
> +	struct xfs_zone_info		*zi = mp->m_zone_info;
> +	struct xfs_zone_reservation	*reservation;
> +
> +	if (list_empty_careful(&zi->zi_reclaim_reservations)) {
> +		xfs_add_freecounter(mp, XC_FREE_RTAVAILABLE, count_fsb);
> +		return;
> +	}
> +
> +	spin_lock(&zi->zi_reservation_lock);
> +	xfs_add_freecounter(mp, XC_FREE_RTAVAILABLE, count_fsb);
> +	count_fsb = xfs_sum_freecounter(mp, XC_FREE_RTAVAILABLE);
> +	list_for_each_entry(reservation, &zi->zi_reclaim_reservations, entry) {
> +		if (reservation->count_fsb > count_fsb)
> +			break;
> +		wake_up_process(reservation->task);
> +		count_fsb -= reservation->count_fsb;
> +
> +	}
> +	spin_unlock(&zi->zi_reservation_lock);
> +}
> +
> +static int
> +xfs_zoned_space_wait_error(
> +	struct xfs_mount		*mp)
> +{
> +	if (xfs_is_shutdown(mp))
> +		return -EIO;
> +	if (fatal_signal_pending(current))
> +		return -EINTR;
> +	return 0;
> +}
> +
> +static int
> +xfs_zoned_reserve_available(
> +	struct xfs_inode		*ip,
> +	xfs_filblks_t			count_fsb,
> +	unsigned int			flags)
> +{
> +	struct xfs_mount		*mp = ip->i_mount;
> +	struct xfs_zone_info		*zi = mp->m_zone_info;
> +	struct xfs_zone_reservation	reservation = {
> +		.task		= current,
> +		.count_fsb	= count_fsb,
> +	};
> +	int				error;
> +
> +	/*
> +	 * If there are no waiters, try to directly grab the available blocks
> +	 * from the percpu counter.
> +	 *
> +	 * If the caller wants to dip into the reserved pool also bypass the
> +	 * wait list.  This relies on the fact that we have a very graciously
> +	 * sized reserved pool that always has enough space.  If the reserved
> +	 * allocations fail we're in trouble.
> +	 */
> +	if (likely(list_empty_careful(&zi->zi_reclaim_reservations) ||
> +	    (flags & XFS_ZR_RESERVED))) {
> +		error = xfs_dec_freecounter(mp, XC_FREE_RTAVAILABLE, count_fsb,
> +				flags & XFS_ZR_RESERVED);
> +		if (error != -ENOSPC)
> +			return error;
> +	}
> +
> +	if (flags & XFS_ZR_NOWAIT)
> +		return -EAGAIN;
> +
> +	spin_lock(&zi->zi_reservation_lock);
> +	list_add_tail(&reservation.entry, &zi->zi_reclaim_reservations);

I think you're supposed to have initialized reservation.entry already.

> +	while ((error = xfs_zoned_space_wait_error(mp)) == 0) {
> +		set_current_state(TASK_KILLABLE);
> +
> +		error = xfs_dec_freecounter(mp, XC_FREE_RTAVAILABLE, count_fsb,
> +				flags & XFS_ZR_RESERVED);
> +		if (error != -ENOSPC)
> +			break;
> +
> +		spin_unlock(&zi->zi_reservation_lock);
> +		schedule();
> +		spin_lock(&zi->zi_reservation_lock);
> +	}
> +	list_del(&reservation.entry);
> +	spin_unlock(&zi->zi_reservation_lock);
> +
> +	__set_current_state(TASK_RUNNING);
> +	return error;
> +}
> +
> +/*
> + * Implement greedy space allocation for short writes by trying to grab all
> + * that is left after locking out other threads from trying to do the same.
> + *
> + * This isn't exactly optimal and can hopefully be replaced by a proper
> + * percpu_counter primitive one day.
> + */
> +static int
> +xfs_zoned_reserve_extents_greedy(
> +	struct xfs_inode		*ip,
> +	xfs_filblks_t			*count_fsb,
> +	unsigned int			flags)
> +{
> +	struct xfs_mount		*mp = ip->i_mount;
> +	struct xfs_zone_info		*zi = mp->m_zone_info;
> +	s64				len = *count_fsb;
> +	int				error = -ENOSPC;
> +
> +	spin_lock(&zi->zi_reservation_lock);
> +	len = min(len, xfs_sum_freecounter(mp, XC_FREE_RTEXTENTS));
> +	if (len > 0) {
> +		*count_fsb = len;
> +		error = xfs_dec_freecounter(mp, XC_FREE_RTEXTENTS, *count_fsb,
> +				flags & XFS_ZR_RESERVED);
> +	}
> +	spin_unlock(&zi->zi_reservation_lock);
> +	return error;
> +}
> +
> +int
> +xfs_zoned_space_reserve(
> +	struct xfs_inode		*ip,
> +	xfs_filblks_t			count_fsb,
> +	unsigned int			flags,
> +	struct xfs_zone_alloc_ctx	*ac)
> +{
> +	struct xfs_mount		*mp = ip->i_mount;
> +	int				error;
> +
> +	ASSERT(ac->reserved_blocks == 0);
> +	ASSERT(ac->open_zone == NULL);
> +
> +	error = xfs_dec_freecounter(mp, XC_FREE_RTEXTENTS, count_fsb,
> +			flags & XFS_ZR_RESERVED);
> +	if (error == -ENOSPC && (flags & XFS_ZR_GREEDY) && count_fsb > 1)
> +		error = xfs_zoned_reserve_extents_greedy(ip, &count_fsb, flags);

Overly long line.

--D

> +	if (error)
> +		return error;
> +
> +	error = xfs_zoned_reserve_available(ip, count_fsb, flags);
> +	if (error) {
> +		xfs_add_freecounter(mp, XC_FREE_RTEXTENTS, count_fsb);
> +		return error;
> +	}
> +	ac->reserved_blocks = count_fsb;
> +	return 0;
> +}
> +
> +void
> +xfs_zoned_space_unreserve(
> +	struct xfs_inode		*ip,
> +	struct xfs_zone_alloc_ctx	*ac)
> +{
> +	if (ac->reserved_blocks > 0) {
> +		struct xfs_mount	*mp = ip->i_mount;
> +
> +		xfs_zoned_add_available(mp, ac->reserved_blocks);
> +		xfs_add_freecounter(mp, XC_FREE_RTEXTENTS, ac->reserved_blocks);
> +	}
> +	if (ac->open_zone)
> +		xfs_open_zone_put(ac->open_zone);
> +}
> -- 
> 2.45.2
> 
>