Re: [PATCH 05/15] xfs: replace dop_low with transaction flag

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Jul 30, 2018 at 12:45:10PM -0400, Brian Foster wrote:
> The dop_low field enables the low free space allocation mode when a
> previous allocation has detected difficulty allocating blocks. It
> has historically been part of the xfs_defer_ops structure, which
> means if enabled, it remains enabled across a set of transactions
> until the deferred operations have completed and the dfops is reset.
> 
> Now that the dfops is embedded in the transaction, we can save a bit
> more space by using a transaction flag rather than a standalone
> boolean. Drop the ->dop_low field and replace it with a transaction
> flag that is set at the same points, carried across rolling
> transactions and cleared on completion of deferred operations. This
> essentially emulates the behavior of ->dop_low and so should not
> change behavior.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_bmap.c       |  8 ++++----
>  fs/xfs/libxfs/xfs_bmap_btree.c |  4 ++--
>  fs/xfs/libxfs/xfs_defer.c      | 16 ++++++++++++++--
>  fs/xfs/libxfs/xfs_defer.h      | 11 -----------
>  fs/xfs/libxfs/xfs_shared.h     | 12 ++++++++++++
>  fs/xfs/xfs_filestream.c        |  3 ++-
>  fs/xfs/xfs_trace.h             | 10 ++--------
>  fs/xfs/xfs_trans.h             |  2 --
>  8 files changed, 36 insertions(+), 30 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index a85c0445b38f..8edf7522aaff 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -700,7 +700,7 @@ xfs_bmap_extents_to_btree(
>  	if (tp->t_firstblock == NULLFSBLOCK) {
>  		args.type = XFS_ALLOCTYPE_START_BNO;
>  		args.fsbno = XFS_INO_TO_FSB(mp, ip->i_ino);
> -	} else if (tp->t_dfops->dop_low) {
> +	} else if (tp->t_flags & XFS_TRANS_LOWMODE) {
>  		args.type = XFS_ALLOCTYPE_START_BNO;
>  		args.fsbno = tp->t_firstblock;
>  	} else {
> @@ -3449,7 +3449,7 @@ xfs_bmap_btalloc(
>  			error = xfs_bmap_btalloc_nullfb(ap, &args, &blen);
>  		if (error)
>  			return error;
> -	} else if (ap->tp->t_dfops->dop_low) {
> +	} else if (ap->tp->t_flags & XFS_TRANS_LOWMODE) {
>  		if (xfs_inode_is_filestream(ap->ip))
>  			args.type = XFS_ALLOCTYPE_FIRST_AG;
>  		else
> @@ -3484,7 +3484,7 @@ xfs_bmap_btalloc(
>  	 * is >= the stripe unit and the allocation offset is
>  	 * at the end of file.
>  	 */
> -	if (!ap->tp->t_dfops->dop_low && ap->aeof) {
> +	if (!(ap->tp->t_flags & XFS_TRANS_LOWMODE) && ap->aeof) {
>  		if (!ap->offset) {
>  			args.alignment = stripe_align;
>  			atype = args.type;
> @@ -3576,7 +3576,7 @@ xfs_bmap_btalloc(
>  		args.total = ap->minlen;
>  		if ((error = xfs_alloc_vextent(&args)))
>  			return error;
> -		ap->tp->t_dfops->dop_low = true;
> +		ap->tp->t_flags |= XFS_TRANS_LOWMODE;
>  	}
>  	if (args.fsbno != NULLFSBLOCK) {
>  		/*
> diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
> index 01489714a253..955e29de8cae 100644
> --- a/fs/xfs/libxfs/xfs_bmap_btree.c
> +++ b/fs/xfs/libxfs/xfs_bmap_btree.c
> @@ -226,7 +226,7 @@ xfs_bmbt_alloc_block(
>  		 * block allocation here and corrupt the filesystem.
>  		 */
>  		args.minleft = args.tp->t_blk_res;
> -	} else if (cur->bc_tp->t_dfops->dop_low) {
> +	} else if (cur->bc_tp->t_flags & XFS_TRANS_LOWMODE) {
>  		args.type = XFS_ALLOCTYPE_START_BNO;
>  	} else {
>  		args.type = XFS_ALLOCTYPE_NEAR_BNO;
> @@ -253,7 +253,7 @@ xfs_bmbt_alloc_block(
>  		error = xfs_alloc_vextent(&args);
>  		if (error)
>  			goto error0;
> -		cur->bc_tp->t_dfops->dop_low = true;
> +		cur->bc_tp->t_flags |= XFS_TRANS_LOWMODE;
>  	}
>  	if (WARN_ON_ONCE(args.fsbno == NULLFSBLOCK)) {
>  		*stat = 0;
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> index e3517a53c525..0306187b5f56 100644
> --- a/fs/xfs/libxfs/xfs_defer.c
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -330,9 +330,14 @@ xfs_defer_reset(
>  
>  	ASSERT(!xfs_defer_has_unfinished_work(dop));
>  
> -	dop->dop_low = false;
>  	memset(dop->dop_inodes, 0, sizeof(dop->dop_inodes));
>  	memset(dop->dop_bufs, 0, sizeof(dop->dop_bufs));
> +
> +	/*
> +	 * Low mode state transfers across transaction rolls to mirror dfops
> +	 * lifetime. Clear it now that dfops is reset.
> +	 */
> +	tp->t_flags &= ~XFS_TRANS_LOWMODE;
>  }
>  
>  /*
> @@ -590,7 +595,14 @@ xfs_defer_move(
>  
>  	memcpy(dst->dop_inodes, src->dop_inodes, sizeof(dst->dop_inodes));
>  	memcpy(dst->dop_bufs, src->dop_bufs, sizeof(dst->dop_bufs));
> -	dst->dop_low = src->dop_low;
> +
> +	/*
> +	 * Low free space mode was historically controlled by a dfops field.
> +	 * This meant that low mode state potentially carried across multiple
> +	 * transaction rolls. Transfer low mode on a dfops move to preserve
> +	 * that behavior.
> +	 */
> +	dtp->t_flags |= stp->t_flags & XFS_TRANS_LOWMODE;
>  
>  	xfs_defer_reset(stp);
>  }
> diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
> index d60c50498fdf..8908a2716774 100644
> --- a/fs/xfs/libxfs/xfs_defer.h
> +++ b/fs/xfs/libxfs/xfs_defer.h
> @@ -25,17 +25,6 @@ struct xfs_defer_pending {
>  
>  /*
>   * Header for deferred operation list.
> - *
> - * dop_low is used by the allocator to activate the lowspace algorithm -
> - * when free space is running low the extent allocator may choose to
> - * allocate an extent from an AG without leaving sufficient space for
> - * a btree split when inserting the new extent.  In this case the allocator
> - * will enable the lowspace algorithm which is supposed to allow further
> - * allocations (such as btree splits and newroots) to allocate from
> - * sequential AGs.  In order to avoid locking AGs out of order the lowspace
> - * algorithm will start searching for free space from AG 0.  If the correct
> - * transaction reservations have been made then this algorithm will eventually
> - * find all the space it needs.
>   */
>  enum xfs_defer_ops_type {
>  	XFS_DEFER_OPS_TYPE_BMAP,
> diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
> index 22089f1c880a..1c5debe748f0 100644
> --- a/fs/xfs/libxfs/xfs_shared.h
> +++ b/fs/xfs/libxfs/xfs_shared.h
> @@ -64,6 +64,18 @@ void	xfs_log_get_max_trans_res(struct xfs_mount *mp,
>  #define XFS_TRANS_RESERVE	0x20    /* OK to use reserved data blocks */
>  #define XFS_TRANS_NO_WRITECOUNT 0x40	/* do not elevate SB writecount */
>  #define XFS_TRANS_NOFS		0x80	/* pass KM_NOFS to kmem_alloc */
> +/*
> + * LOWMODE is used by the allocator to activate the lowspace algorithm - when
> + * free space is running low the extent allocator may choose to allocate an
> + * extent from an AG without leaving sufficient space for a btree split when
> + * inserting the new extent. In this case the allocator will enable the
> + * lowspace algorithm which is supposed to allow further allocations (such as
> + * btree splits and newroots) to allocate from sequential AGs. In order to
> + * avoid locking AGs out of order the lowspace algorithm will start searching
> + * for free space from AG 0. If the correct transaction reservations have been
> + * made then this algorithm will eventually find all the space it needs.
> + */
> +#define XFS_TRANS_LOWMODE	0x100	/* allocate in low space mode */
>  
>  /*
>   * Field values for xfs_trans_mod_sb.
> diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
> index 212173c62588..182501373af2 100644
> --- a/fs/xfs/xfs_filestream.c
> +++ b/fs/xfs/xfs_filestream.c
> @@ -20,6 +20,7 @@
>  #include "xfs_trace.h"
>  #include "xfs_ag_resv.h"
>  #include "xfs_trans.h"
> +#include "xfs_shared.h"
>  
>  struct xfs_fstrm_item {
>  	struct xfs_mru_cache_elem	mru;
> @@ -378,7 +379,7 @@ xfs_filestream_new_ag(
>  
>  	if (xfs_alloc_is_userdata(ap->datatype))
>  		flags |= XFS_PICK_USERDATA;
> -	if (ap->tp->t_dfops->dop_low)
> +	if (ap->tp->t_flags & XFS_TRANS_LOWMODE)
>  		flags |= XFS_PICK_LOWSPACE;
>  
>  	err = xfs_filestream_pick_ag(pip, startag, agp, flags, minlen);
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index cc6995cfce66..8807f1bb814a 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -2223,19 +2223,16 @@ DECLARE_EVENT_CLASS(xfs_defer_class,
>  		__field(dev_t, dev)
>  		__field(void *, dop)
>  		__field(char, committed)
> -		__field(char, low)
>  		__field(unsigned long, caller_ip)
>  	),
>  	TP_fast_assign(
>  		__entry->dev = mp ? mp->m_super->s_dev : 0;
>  		__entry->dop = dop;
> -		__entry->low = dop->dop_low;
>  		__entry->caller_ip = caller_ip;
>  	),
> -	TP_printk("dev %d:%d ops %p low %d, caller %pS",
> +	TP_printk("dev %d:%d ops %p caller %pS",
>  		  MAJOR(__entry->dev), MINOR(__entry->dev),
>  		  __entry->dop,
> -		  __entry->low,
>  		  (char *)__entry->caller_ip)
>  )
>  #define DEFINE_DEFER_EVENT(name) \
> @@ -2251,19 +2248,16 @@ DECLARE_EVENT_CLASS(xfs_defer_error_class,
>  		__field(dev_t, dev)
>  		__field(void *, dop)
>  		__field(char, committed)
> -		__field(char, low)
>  		__field(int, error)
>  	),
>  	TP_fast_assign(
>  		__entry->dev = mp ? mp->m_super->s_dev : 0;
>  		__entry->dop = dop;
> -		__entry->low = dop->dop_low;
>  		__entry->error = error;
>  	),
> -	TP_printk("dev %d:%d ops %p low %d err %d",
> +	TP_printk("dev %d:%d ops %p err %d",
>  		  MAJOR(__entry->dev), MINOR(__entry->dev),
>  		  __entry->dop,
> -		  __entry->low,
>  		  __entry->error)
>  )
>  #define DEFINE_DEFER_ERROR_EVENT(name) \
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index dc79e3c1d3e8..7e493221160e 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -101,8 +101,6 @@ struct xfs_defer_ops {
>  	/* relog these with each roll */
>  	struct xfs_inode	*dop_inodes[XFS_DEFER_OPS_NR_INODES];
>  	struct xfs_buf		*dop_bufs[XFS_DEFER_OPS_NR_BUFS];
> -
> -	bool			dop_low;	/* alloc in low mode */
>  };
>  
>  /*
> -- 
> 2.17.1
> 
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