diff mbox series

[v8,3/5] xfs: introduce xfs_ag_shrink_space()

Message ID 20210305025703.3069469-4-hsiangkao@redhat.com (mailing list archive)
State Superseded, archived
Headers show
Series xfs: support shrinking free space in the last AG | expand

Commit Message

Gao Xiang March 5, 2021, 2:57 a.m. UTC
This patch introduces a helper to shrink unused space in the last AG
by fixing up the freespace btree.

Also make sure that the per-AG reservation works under the new AG
size. If such per-AG reservation or extent allocation fails, roll
the transaction so the new transaction could cancel without any side
effects.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
 fs/xfs/libxfs/xfs_ag.h |   4 +-
 2 files changed, 114 insertions(+), 1 deletion(-)

Comments

Darrick J. Wong March 9, 2021, 6:05 p.m. UTC | #1
On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> This patch introduces a helper to shrink unused space in the last AG
> by fixing up the freespace btree.
> 
> Also make sure that the per-AG reservation works under the new AG
> size. If such per-AG reservation or extent allocation fails, roll
> the transaction so the new transaction could cancel without any side
> effects.
> 
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Looks fine, moving on to examining the fstests...

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_ag.h |   4 +-
>  2 files changed, 114 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index 9331f3516afa..1f6f9e70e1cb 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -22,6 +22,11 @@
>  #include "xfs_ag.h"
>  #include "xfs_ag_resv.h"
>  #include "xfs_health.h"
> +#include "xfs_error.h"
> +#include "xfs_bmap.h"
> +#include "xfs_defer.h"
> +#include "xfs_log_format.h"
> +#include "xfs_trans.h"
>  
>  static int
>  xfs_get_aghdr_buf(
> @@ -485,6 +490,112 @@ xfs_ag_init_headers(
>  	return error;
>  }
>  
> +int
> +xfs_ag_shrink_space(
> +	struct xfs_mount	*mp,
> +	struct xfs_trans	**tpp,
> +	xfs_agnumber_t		agno,
> +	xfs_extlen_t		delta)
> +{
> +	struct xfs_alloc_arg	args = {
> +		.tp	= *tpp,
> +		.mp	= mp,
> +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> +		.minlen = delta,
> +		.maxlen = delta,
> +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> +		.resv	= XFS_AG_RESV_NONE,
> +		.prod	= 1
> +	};
> +	struct xfs_buf		*agibp, *agfbp;
> +	struct xfs_agi		*agi;
> +	struct xfs_agf		*agf;
> +	int			error, err2;
> +
> +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> +	if (error)
> +		return error;
> +
> +	agi = agibp->b_addr;
> +
> +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> +	if (error)
> +		return error;
> +
> +	agf = agfbp->b_addr;
> +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> +		return -EFSCORRUPTED;
> +
> +	if (delta >= agi->agi_length)
> +		return -EINVAL;
> +
> +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> +				    be32_to_cpu(agi->agi_length) - delta);
> +
> +	/* remove the preallocations before allocation and re-establish then */
> +	error = xfs_ag_resv_free(agibp->b_pag);
> +	if (error)
> +		return error;
> +
> +	/* internal log shouldn't also show up in the free space btrees */
> +	error = xfs_alloc_vextent(&args);
> +	if (!error && args.agbno == NULLAGBLOCK)
> +		error = -ENOSPC;
> +
> +	if (error) {
> +		/*
> +		 * if extent allocation fails, need to roll the transaction to
> +		 * ensure that the AGFL fixup has been committed anyway.
> +		 */
> +		err2 = xfs_trans_roll(tpp);
> +		if (err2)
> +			return err2;
> +		goto resv_init_out;
> +	}
> +
> +	/*
> +	 * if successfully deleted from freespace btrees, need to confirm
> +	 * per-AG reservation works as expected.
> +	 */
> +	be32_add_cpu(&agi->agi_length, -delta);
> +	be32_add_cpu(&agf->agf_length, -delta);
> +
> +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> +	if (err2) {
> +		be32_add_cpu(&agi->agi_length, delta);
> +		be32_add_cpu(&agf->agf_length, delta);
> +		if (err2 != -ENOSPC)
> +			goto resv_err;
> +
> +		__xfs_bmap_add_free(*tpp, args.fsbno, delta, NULL, true);
> +
> +		/*
> +		 * Roll the transaction before trying to re-init the per-ag
> +		 * reservation. The new transaction is clean so it will cancel
> +		 * without any side effects.
> +		 */
> +		error = xfs_defer_finish(tpp);
> +		if (error)
> +			return error;
> +
> +		error = -ENOSPC;
> +		goto resv_init_out;
> +	}
> +	xfs_ialloc_log_agi(*tpp, agibp, XFS_AGI_LENGTH);
> +	xfs_alloc_log_agf(*tpp, agfbp, XFS_AGF_LENGTH);
> +	return 0;
> +
> +resv_init_out:
> +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> +	if (!err2)
> +		return error;
> +resv_err:
> +	xfs_warn(mp, "Error %d reserving per-AG metadata reserve pool.", err2);
> +	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> +	return err2;
> +}
> +
>  /*
>   * Extent the AG indicated by the @id by the length passed in
>   */
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 5166322807e7..41293ebde8da 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -24,8 +24,10 @@ struct aghdr_init_data {
>  };
>  
>  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> +			xfs_agnumber_t agno, xfs_extlen_t len);
>  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> -			struct aghdr_init_data *id, xfs_extlen_t len);
> +			struct aghdr_init_data *id, xfs_extlen_t delta);
>  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
>  			struct xfs_ag_geometry *ageo);
>  
> -- 
> 2.27.0
>
Brian Foster March 22, 2021, 11:30 a.m. UTC | #2
On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> This patch introduces a helper to shrink unused space in the last AG
> by fixing up the freespace btree.
> 
> Also make sure that the per-AG reservation works under the new AG
> size. If such per-AG reservation or extent allocation fails, roll
> the transaction so the new transaction could cancel without any side
> effects.
> 
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---

Looks mostly good to me. Some nits..

>  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_ag.h |   4 +-
>  2 files changed, 114 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index 9331f3516afa..1f6f9e70e1cb 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
...
> @@ -485,6 +490,112 @@ xfs_ag_init_headers(
>  	return error;
>  }
>  
> +int
> +xfs_ag_shrink_space(
> +	struct xfs_mount	*mp,
> +	struct xfs_trans	**tpp,
> +	xfs_agnumber_t		agno,
> +	xfs_extlen_t		delta)
> +{
> +	struct xfs_alloc_arg	args = {
> +		.tp	= *tpp,
> +		.mp	= mp,
> +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> +		.minlen = delta,
> +		.maxlen = delta,
> +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> +		.resv	= XFS_AG_RESV_NONE,
> +		.prod	= 1
> +	};
> +	struct xfs_buf		*agibp, *agfbp;
> +	struct xfs_agi		*agi;
> +	struct xfs_agf		*agf;
> +	int			error, err2;
> +
> +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> +	if (error)
> +		return error;
> +
> +	agi = agibp->b_addr;
> +
> +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> +	if (error)
> +		return error;
> +
> +	agf = agfbp->b_addr;
> +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> +		return -EFSCORRUPTED;

Is this check here for a reason? It seems a bit random, so I wonder if
we should just leave the extra verification to buffer verifiers.

> +
> +	if (delta >= agi->agi_length)
> +		return -EINVAL;
> +
> +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> +				    be32_to_cpu(agi->agi_length) - delta);
> +
> +	/* remove the preallocations before allocation and re-establish then */

The comment is a little confusing. Perhaps something like the following,
if accurate..?

/*
 * Disable perag reservations so it doesn't cause the allocation request
 * to fail. We'll reestablish reservation before we return.
 */

> +	error = xfs_ag_resv_free(agibp->b_pag);
> +	if (error)
> +		return error;
> +
> +	/* internal log shouldn't also show up in the free space btrees */
> +	error = xfs_alloc_vextent(&args);
> +	if (!error && args.agbno == NULLAGBLOCK)
> +		error = -ENOSPC;
> +
> +	if (error) {
> +		/*
> +		 * if extent allocation fails, need to roll the transaction to
> +		 * ensure that the AGFL fixup has been committed anyway.
> +		 */
> +		err2 = xfs_trans_roll(tpp);
> +		if (err2)
> +			return err2;
> +		goto resv_init_out;

So if this fails and the transaction rolls, do we still hold the agi/agf
buffers here? If not, there might be a window of time where it's
possible for some other task to come in and alloc out of the AG without
the perag res being active.

> +	}
> +
> +	/*
> +	 * if successfully deleted from freespace btrees, need to confirm
> +	 * per-AG reservation works as expected.
> +	 */
> +	be32_add_cpu(&agi->agi_length, -delta);
> +	be32_add_cpu(&agf->agf_length, -delta);
> +
> +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> +	if (err2) {
> +		be32_add_cpu(&agi->agi_length, delta);
> +		be32_add_cpu(&agf->agf_length, delta);
> +		if (err2 != -ENOSPC)
> +			goto resv_err;
> +
> +		__xfs_bmap_add_free(*tpp, args.fsbno, delta, NULL, true);
> +
> +		/*
> +		 * Roll the transaction before trying to re-init the per-ag
> +		 * reservation. The new transaction is clean so it will cancel
> +		 * without any side effects.
> +		 */
> +		error = xfs_defer_finish(tpp);
> +		if (error)
> +			return error;
> +
> +		error = -ENOSPC;
> +		goto resv_init_out;
> +	}
> +	xfs_ialloc_log_agi(*tpp, agibp, XFS_AGI_LENGTH);
> +	xfs_alloc_log_agf(*tpp, agfbp, XFS_AGF_LENGTH);
> +	return 0;
> +
> +resv_init_out:
> +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> +	if (!err2)
> +		return error;
> +resv_err:
> +	xfs_warn(mp, "Error %d reserving per-AG metadata reserve pool.", err2);
> +	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> +	return err2;
> +}
> +
>  /*
>   * Extent the AG indicated by the @id by the length passed in
>   */
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 5166322807e7..41293ebde8da 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -24,8 +24,10 @@ struct aghdr_init_data {
>  };
>  
>  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> +			xfs_agnumber_t agno, xfs_extlen_t len);
>  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> -			struct aghdr_init_data *id, xfs_extlen_t len);
> +			struct aghdr_init_data *id, xfs_extlen_t delta);

This looks misplaced..?

Or maybe this is trying to make the APIs consistent, but the function
definition still uses len as well as the declaration for
_ag_shrink_space() (while the definition of that function uses delta).

FWIW, the name delta tends to suggest a signed value to me based on our
pattern of usage, whereas here it seems like these helpers always want a
positive value (i.e. a length).

Brian

>  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
>  			struct xfs_ag_geometry *ageo);
>  
> -- 
> 2.27.0
>
Gao Xiang March 22, 2021, 12:03 p.m. UTC | #3
Hi Brian,

On Mon, Mar 22, 2021 at 07:30:03AM -0400, Brian Foster wrote:
> On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> > This patch introduces a helper to shrink unused space in the last AG
> > by fixing up the freespace btree.
> > 
> > Also make sure that the per-AG reservation works under the new AG
> > size. If such per-AG reservation or extent allocation fails, roll
> > the transaction so the new transaction could cancel without any side
> > effects.
> > 
> > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > ---
> 
> Looks mostly good to me. Some nits..
> 
> >  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
> >  fs/xfs/libxfs/xfs_ag.h |   4 +-
> >  2 files changed, 114 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > index 9331f3516afa..1f6f9e70e1cb 100644
> > --- a/fs/xfs/libxfs/xfs_ag.c
> > +++ b/fs/xfs/libxfs/xfs_ag.c
> ...
> > @@ -485,6 +490,112 @@ xfs_ag_init_headers(
> >  	return error;
> >  }
> >  
> > +int
> > +xfs_ag_shrink_space(
> > +	struct xfs_mount	*mp,
> > +	struct xfs_trans	**tpp,
> > +	xfs_agnumber_t		agno,
> > +	xfs_extlen_t		delta)
> > +{
> > +	struct xfs_alloc_arg	args = {
> > +		.tp	= *tpp,
> > +		.mp	= mp,
> > +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> > +		.minlen = delta,
> > +		.maxlen = delta,
> > +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> > +		.resv	= XFS_AG_RESV_NONE,
> > +		.prod	= 1
> > +	};
> > +	struct xfs_buf		*agibp, *agfbp;
> > +	struct xfs_agi		*agi;
> > +	struct xfs_agf		*agf;
> > +	int			error, err2;
> > +
> > +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> > +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> > +	if (error)
> > +		return error;
> > +
> > +	agi = agibp->b_addr;
> > +
> > +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> > +	if (error)
> > +		return error;
> > +
> > +	agf = agfbp->b_addr;
> > +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > +		return -EFSCORRUPTED;
> 
> Is this check here for a reason? It seems a bit random, so I wonder if
> we should just leave the extra verification to buffer verifiers.

It came from Darrick's thought. I'm fine with either way, but I feel
confused if different conflict opinions here:
https://lore.kernel.org/linux-xfs/20210303181931.GB3419940@magnolia/

> 
> > +
> > +	if (delta >= agi->agi_length)
> > +		return -EINVAL;
> > +
> > +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> > +				    be32_to_cpu(agi->agi_length) - delta);
> > +
> > +	/* remove the preallocations before allocation and re-establish then */
> 
> The comment is a little confusing. Perhaps something like the following,
> if accurate..?
> 
> /*
>  * Disable perag reservations so it doesn't cause the allocation request
>  * to fail. We'll reestablish reservation before we return.
>  */

ok, will update in the next version.

> 
> > +	error = xfs_ag_resv_free(agibp->b_pag);
> > +	if (error)
> > +		return error;
> > +
> > +	/* internal log shouldn't also show up in the free space btrees */
> > +	error = xfs_alloc_vextent(&args);
> > +	if (!error && args.agbno == NULLAGBLOCK)
> > +		error = -ENOSPC;
> > +
> > +	if (error) {
> > +		/*
> > +		 * if extent allocation fails, need to roll the transaction to
> > +		 * ensure that the AGFL fixup has been committed anyway.
> > +		 */
> > +		err2 = xfs_trans_roll(tpp);
> > +		if (err2)
> > +			return err2;
> > +		goto resv_init_out;
> 
> So if this fails and the transaction rolls, do we still hold the agi/agf
> buffers here? If not, there might be a window of time where it's
> possible for some other task to come in and alloc out of the AG without
> the perag res being active.

Yeah, I might need to bhold this, will update.

> 
> > +	}
> > +
> > +	/*
> > +	 * if successfully deleted from freespace btrees, need to confirm
> > +	 * per-AG reservation works as expected.
> > +	 */
> > +	be32_add_cpu(&agi->agi_length, -delta);
> > +	be32_add_cpu(&agf->agf_length, -delta);
> > +
> > +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> > +	if (err2) {
> > +		be32_add_cpu(&agi->agi_length, delta);
> > +		be32_add_cpu(&agf->agf_length, delta);
> > +		if (err2 != -ENOSPC)
> > +			goto resv_err;
> > +
> > +		__xfs_bmap_add_free(*tpp, args.fsbno, delta, NULL, true);
> > +
> > +		/*
> > +		 * Roll the transaction before trying to re-init the per-ag
> > +		 * reservation. The new transaction is clean so it will cancel
> > +		 * without any side effects.
> > +		 */
> > +		error = xfs_defer_finish(tpp);
> > +		if (error)
> > +			return error;
> > +
> > +		error = -ENOSPC;
> > +		goto resv_init_out;
> > +	}
> > +	xfs_ialloc_log_agi(*tpp, agibp, XFS_AGI_LENGTH);
> > +	xfs_alloc_log_agf(*tpp, agfbp, XFS_AGF_LENGTH);
> > +	return 0;
> > +
> > +resv_init_out:
> > +	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> > +	if (!err2)
> > +		return error;
> > +resv_err:
> > +	xfs_warn(mp, "Error %d reserving per-AG metadata reserve pool.", err2);
> > +	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> > +	return err2;
> > +}
> > +
> >  /*
> >   * Extent the AG indicated by the @id by the length passed in
> >   */
> > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> > index 5166322807e7..41293ebde8da 100644
> > --- a/fs/xfs/libxfs/xfs_ag.h
> > +++ b/fs/xfs/libxfs/xfs_ag.h
> > @@ -24,8 +24,10 @@ struct aghdr_init_data {
> >  };
> >  
> >  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> > +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> > +			xfs_agnumber_t agno, xfs_extlen_t len);
> >  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> > -			struct aghdr_init_data *id, xfs_extlen_t len);
> > +			struct aghdr_init_data *id, xfs_extlen_t delta);
> 
> This looks misplaced..?
> 
> Or maybe this is trying to make the APIs consistent, but the function
> definition still uses len as well as the declaration for
> _ag_shrink_space() (while the definition of that function uses delta).
> 
> FWIW, the name delta tends to suggest a signed value to me based on our
> pattern of usage, whereas here it seems like these helpers always want a
> positive value (i.e. a length).

Yeah, it's just misplaced, thanks for pointing out, sorry about that.
`delta' name came from, `len' is confusing to Darrick.
https://lore.kernel.org/r/20210303182527.GC3419940@magnolia/

Thanks,
Gao Xiang

> 
> Brian
> 
> >  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
> >  			struct xfs_ag_geometry *ageo);
> >  
> > -- 
> > 2.27.0
> > 
>
Brian Foster March 22, 2021, 12:25 p.m. UTC | #4
On Mon, Mar 22, 2021 at 08:03:10PM +0800, Gao Xiang wrote:
> Hi Brian,
> 
> On Mon, Mar 22, 2021 at 07:30:03AM -0400, Brian Foster wrote:
> > On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> > > This patch introduces a helper to shrink unused space in the last AG
> > > by fixing up the freespace btree.
> > > 
> > > Also make sure that the per-AG reservation works under the new AG
> > > size. If such per-AG reservation or extent allocation fails, roll
> > > the transaction so the new transaction could cancel without any side
> > > effects.
> > > 
> > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > > ---
> > 
> > Looks mostly good to me. Some nits..
> > 
> > >  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
> > >  fs/xfs/libxfs/xfs_ag.h |   4 +-
> > >  2 files changed, 114 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > > index 9331f3516afa..1f6f9e70e1cb 100644
> > > --- a/fs/xfs/libxfs/xfs_ag.c
> > > +++ b/fs/xfs/libxfs/xfs_ag.c
> > ...
> > > @@ -485,6 +490,112 @@ xfs_ag_init_headers(
> > >  	return error;
> > >  }
> > >  
> > > +int
> > > +xfs_ag_shrink_space(
> > > +	struct xfs_mount	*mp,
> > > +	struct xfs_trans	**tpp,
> > > +	xfs_agnumber_t		agno,
> > > +	xfs_extlen_t		delta)
> > > +{
> > > +	struct xfs_alloc_arg	args = {
> > > +		.tp	= *tpp,
> > > +		.mp	= mp,
> > > +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> > > +		.minlen = delta,
> > > +		.maxlen = delta,
> > > +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> > > +		.resv	= XFS_AG_RESV_NONE,
> > > +		.prod	= 1
> > > +	};
> > > +	struct xfs_buf		*agibp, *agfbp;
> > > +	struct xfs_agi		*agi;
> > > +	struct xfs_agf		*agf;
> > > +	int			error, err2;
> > > +
> > > +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> > > +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> > > +	if (error)
> > > +		return error;
> > > +
> > > +	agi = agibp->b_addr;
> > > +
> > > +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> > > +	if (error)
> > > +		return error;
> > > +
> > > +	agf = agfbp->b_addr;
> > > +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > > +		return -EFSCORRUPTED;
> > 
> > Is this check here for a reason? It seems a bit random, so I wonder if
> > we should just leave the extra verification to buffer verifiers.
> 
> It came from Darrick's thought. I'm fine with either way, but I feel
> confused if different conflict opinions here:
> https://lore.kernel.org/linux-xfs/20210303181931.GB3419940@magnolia/
> 

Darrick's comment seems to refer to the check below. I'm referring to
the check above that agi_length and agf_length match. Are they intended
to go together? The check above seems to preexist the one below.

Anyways, if so, maybe just bunch them together and add a comment:

	/* some extra paranoid checks before we shrink the ag */
	if (XFS_IS_CORRUPT(...))
		return -EFSCORRUPTED;
	if (delta >= agf->agf_length)
		return -EVINAL; 

> > 
> > > +
> > > +	if (delta >= agi->agi_length)
> > > +		return -EINVAL;
> > > +
> > > +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> > > +				    be32_to_cpu(agi->agi_length) - delta);
> > > +
> > > +	/* remove the preallocations before allocation and re-establish then */
...
> > > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> > > index 5166322807e7..41293ebde8da 100644
> > > --- a/fs/xfs/libxfs/xfs_ag.h
> > > +++ b/fs/xfs/libxfs/xfs_ag.h
> > > @@ -24,8 +24,10 @@ struct aghdr_init_data {
> > >  };
> > >  
> > >  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> > > +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> > > +			xfs_agnumber_t agno, xfs_extlen_t len);
> > >  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> > > -			struct aghdr_init_data *id, xfs_extlen_t len);
> > > +			struct aghdr_init_data *id, xfs_extlen_t delta);
> > 
> > This looks misplaced..?
> > 
> > Or maybe this is trying to make the APIs consistent, but the function
> > definition still uses len as well as the declaration for
> > _ag_shrink_space() (while the definition of that function uses delta).
> > 
> > FWIW, the name delta tends to suggest a signed value to me based on our
> > pattern of usage, whereas here it seems like these helpers always want a
> > positive value (i.e. a length).
> 
> Yeah, it's just misplaced, thanks for pointing out, sorry about that.
> `delta' name came from, `len' is confusing to Darrick.
> https://lore.kernel.org/r/20210303182527.GC3419940@magnolia/
> 

Fair enough. I'm not worried about the name, just pointing out some
potential inconsistencies.

Brian

> Thanks,
> Gao Xiang
> 
> > 
> > Brian
> > 
> > >  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
> > >  			struct xfs_ag_geometry *ageo);
> > >  
> > > -- 
> > > 2.27.0
> > > 
> > 
>
Gao Xiang March 22, 2021, 12:33 p.m. UTC | #5
On Mon, Mar 22, 2021 at 08:25:55AM -0400, Brian Foster wrote:
> On Mon, Mar 22, 2021 at 08:03:10PM +0800, Gao Xiang wrote:
> > Hi Brian,
> > 
> > On Mon, Mar 22, 2021 at 07:30:03AM -0400, Brian Foster wrote:
> > > On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> > > > This patch introduces a helper to shrink unused space in the last AG
> > > > by fixing up the freespace btree.
> > > > 
> > > > Also make sure that the per-AG reservation works under the new AG
> > > > size. If such per-AG reservation or extent allocation fails, roll
> > > > the transaction so the new transaction could cancel without any side
> > > > effects.
> > > > 
> > > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > > > ---
> > > 
> > > Looks mostly good to me. Some nits..
> > > 
> > > >  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
> > > >  fs/xfs/libxfs/xfs_ag.h |   4 +-
> > > >  2 files changed, 114 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > > > index 9331f3516afa..1f6f9e70e1cb 100644
> > > > --- a/fs/xfs/libxfs/xfs_ag.c
> > > > +++ b/fs/xfs/libxfs/xfs_ag.c
> > > ...
> > > > @@ -485,6 +490,112 @@ xfs_ag_init_headers(
> > > >  	return error;
> > > >  }
> > > >  
> > > > +int
> > > > +xfs_ag_shrink_space(
> > > > +	struct xfs_mount	*mp,
> > > > +	struct xfs_trans	**tpp,
> > > > +	xfs_agnumber_t		agno,
> > > > +	xfs_extlen_t		delta)
> > > > +{
> > > > +	struct xfs_alloc_arg	args = {
> > > > +		.tp	= *tpp,
> > > > +		.mp	= mp,
> > > > +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> > > > +		.minlen = delta,
> > > > +		.maxlen = delta,
> > > > +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> > > > +		.resv	= XFS_AG_RESV_NONE,
> > > > +		.prod	= 1
> > > > +	};
> > > > +	struct xfs_buf		*agibp, *agfbp;
> > > > +	struct xfs_agi		*agi;
> > > > +	struct xfs_agf		*agf;
> > > > +	int			error, err2;
> > > > +
> > > > +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> > > > +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> > > > +	if (error)
> > > > +		return error;
> > > > +
> > > > +	agi = agibp->b_addr;
> > > > +
> > > > +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> > > > +	if (error)
> > > > +		return error;
> > > > +
> > > > +	agf = agfbp->b_addr;
> > > > +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > > > +		return -EFSCORRUPTED;
> > > 
> > > Is this check here for a reason? It seems a bit random, so I wonder if
> > > we should just leave the extra verification to buffer verifiers.
> > 
> > It came from Darrick's thought. I'm fine with either way, but I feel
> > confused if different conflict opinions here:
> > https://lore.kernel.org/linux-xfs/20210303181931.GB3419940@magnolia/
> > 
> 
> Darrick's comment seems to refer to the check below. I'm referring to
> the check above that agi_length and agf_length match. Are they intended
> to go together? The check above seems to preexist the one below.

Sorry, update link of this:
https://lore.kernel.org/r/20210111181753.GC1164246@magnolia/

> 
> Anyways, if so, maybe just bunch them together and add a comment:
> 
> 	/* some extra paranoid checks before we shrink the ag */
> 	if (XFS_IS_CORRUPT(...))
> 		return -EFSCORRUPTED;
> 	if (delta >= agf->agf_length)
> 		return -EVINAL; 
> 

ok, will update this.

> > > 
> > > > +
> > > > +	if (delta >= agi->agi_length)
> > > > +		return -EINVAL;
> > > > +
> > > > +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> > > > +				    be32_to_cpu(agi->agi_length) - delta);
> > > > +
> > > > +	/* remove the preallocations before allocation and re-establish then */
> ...
> > > > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> > > > index 5166322807e7..41293ebde8da 100644
> > > > --- a/fs/xfs/libxfs/xfs_ag.h
> > > > +++ b/fs/xfs/libxfs/xfs_ag.h
> > > > @@ -24,8 +24,10 @@ struct aghdr_init_data {
> > > >  };
> > > >  
> > > >  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> > > > +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> > > > +			xfs_agnumber_t agno, xfs_extlen_t len);
> > > >  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> > > > -			struct aghdr_init_data *id, xfs_extlen_t len);
> > > > +			struct aghdr_init_data *id, xfs_extlen_t delta);
> > > 
> > > This looks misplaced..?
> > > 
> > > Or maybe this is trying to make the APIs consistent, but the function
> > > definition still uses len as well as the declaration for
> > > _ag_shrink_space() (while the definition of that function uses delta).
> > > 
> > > FWIW, the name delta tends to suggest a signed value to me based on our
> > > pattern of usage, whereas here it seems like these helpers always want a
> > > positive value (i.e. a length).
> > 
> > Yeah, it's just misplaced, thanks for pointing out, sorry about that.
> > `delta' name came from, `len' is confusing to Darrick.
> > https://lore.kernel.org/r/20210303182527.GC3419940@magnolia/
> > 
> 
> Fair enough. I'm not worried about the name, just pointing out some
> potential inconsistencies.

Thanks for pointing out!

Thanks,
Gao Xiang

> 
> Brian
> 
> > Thanks,
> > Gao Xiang
> > 
> > > 
> > > Brian
> > > 
> > > >  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
> > > >  			struct xfs_ag_geometry *ageo);
> > > >  
> > > > -- 
> > > > 2.27.0
> > > > 
> > > 
> > 
>
Darrick J. Wong March 22, 2021, 4:38 p.m. UTC | #6
On Mon, Mar 22, 2021 at 08:33:28PM +0800, Gao Xiang wrote:
> On Mon, Mar 22, 2021 at 08:25:55AM -0400, Brian Foster wrote:
> > On Mon, Mar 22, 2021 at 08:03:10PM +0800, Gao Xiang wrote:
> > > Hi Brian,
> > > 
> > > On Mon, Mar 22, 2021 at 07:30:03AM -0400, Brian Foster wrote:
> > > > On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> > > > > This patch introduces a helper to shrink unused space in the last AG
> > > > > by fixing up the freespace btree.
> > > > > 
> > > > > Also make sure that the per-AG reservation works under the new AG
> > > > > size. If such per-AG reservation or extent allocation fails, roll
> > > > > the transaction so the new transaction could cancel without any side
> > > > > effects.
> > > > > 
> > > > > Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> > > > > ---
> > > > 
> > > > Looks mostly good to me. Some nits..
> > > > 
> > > > >  fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
> > > > >  fs/xfs/libxfs/xfs_ag.h |   4 +-
> > > > >  2 files changed, 114 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > > > > index 9331f3516afa..1f6f9e70e1cb 100644
> > > > > --- a/fs/xfs/libxfs/xfs_ag.c
> > > > > +++ b/fs/xfs/libxfs/xfs_ag.c
> > > > ...
> > > > > @@ -485,6 +490,112 @@ xfs_ag_init_headers(
> > > > >  	return error;
> > > > >  }
> > > > >  
> > > > > +int
> > > > > +xfs_ag_shrink_space(
> > > > > +	struct xfs_mount	*mp,
> > > > > +	struct xfs_trans	**tpp,
> > > > > +	xfs_agnumber_t		agno,
> > > > > +	xfs_extlen_t		delta)
> > > > > +{
> > > > > +	struct xfs_alloc_arg	args = {
> > > > > +		.tp	= *tpp,
> > > > > +		.mp	= mp,
> > > > > +		.type	= XFS_ALLOCTYPE_THIS_BNO,
> > > > > +		.minlen = delta,
> > > > > +		.maxlen = delta,
> > > > > +		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
> > > > > +		.resv	= XFS_AG_RESV_NONE,
> > > > > +		.prod	= 1
> > > > > +	};
> > > > > +	struct xfs_buf		*agibp, *agfbp;
> > > > > +	struct xfs_agi		*agi;
> > > > > +	struct xfs_agf		*agf;
> > > > > +	int			error, err2;
> > > > > +
> > > > > +	ASSERT(agno == mp->m_sb.sb_agcount - 1);
> > > > > +	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> > > > > +	if (error)
> > > > > +		return error;
> > > > > +
> > > > > +	agi = agibp->b_addr;
> > > > > +
> > > > > +	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> > > > > +	if (error)
> > > > > +		return error;
> > > > > +
> > > > > +	agf = agfbp->b_addr;
> > > > > +	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > > > > +		return -EFSCORRUPTED;
> > > > 
> > > > Is this check here for a reason? It seems a bit random, so I wonder if
> > > > we should just leave the extra verification to buffer verifiers.
> > > 
> > > It came from Darrick's thought. I'm fine with either way, but I feel
> > > confused if different conflict opinions here:
> > > https://lore.kernel.org/linux-xfs/20210303181931.GB3419940@magnolia/
> > > 
> > 
> > Darrick's comment seems to refer to the check below. I'm referring to
> > the check above that agi_length and agf_length match. Are they intended
> > to go together? The check above seems to preexist the one below.
> 
> Sorry, update link of this:
> https://lore.kernel.org/r/20210111181753.GC1164246@magnolia/
> 
> > 
> > Anyways, if so, maybe just bunch them together and add a comment:
> > 
> > 	/* some extra paranoid checks before we shrink the ag */

Yes, all this is born out of paranoia checks on my part because I feel
that shrink is likely to have Real Bad Dataloss Consequences(tm) if we
don't check everything a second time before proceeding.

--D

> > 	if (XFS_IS_CORRUPT(...))
> > 		return -EFSCORRUPTED;
> > 	if (delta >= agf->agf_length)
> > 		return -EVINAL; 
> > 
> 
> ok, will update this.
> 
> > > > 
> > > > > +
> > > > > +	if (delta >= agi->agi_length)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> > > > > +				    be32_to_cpu(agi->agi_length) - delta);
> > > > > +
> > > > > +	/* remove the preallocations before allocation and re-establish then */
> > ...
> > > > > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> > > > > index 5166322807e7..41293ebde8da 100644
> > > > > --- a/fs/xfs/libxfs/xfs_ag.h
> > > > > +++ b/fs/xfs/libxfs/xfs_ag.h
> > > > > @@ -24,8 +24,10 @@ struct aghdr_init_data {
> > > > >  };
> > > > >  
> > > > >  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> > > > > +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> > > > > +			xfs_agnumber_t agno, xfs_extlen_t len);
> > > > >  int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> > > > > -			struct aghdr_init_data *id, xfs_extlen_t len);
> > > > > +			struct aghdr_init_data *id, xfs_extlen_t delta);
> > > > 
> > > > This looks misplaced..?
> > > > 
> > > > Or maybe this is trying to make the APIs consistent, but the function
> > > > definition still uses len as well as the declaration for
> > > > _ag_shrink_space() (while the definition of that function uses delta).
> > > > 
> > > > FWIW, the name delta tends to suggest a signed value to me based on our
> > > > pattern of usage, whereas here it seems like these helpers always want a
> > > > positive value (i.e. a length).
> > > 
> > > Yeah, it's just misplaced, thanks for pointing out, sorry about that.
> > > `delta' name came from, `len' is confusing to Darrick.
> > > https://lore.kernel.org/r/20210303182527.GC3419940@magnolia/
> > > 
> > 
> > Fair enough. I'm not worried about the name, just pointing out some
> > potential inconsistencies.
> 
> Thanks for pointing out!
> 
> Thanks,
> Gao Xiang
> 
> > 
> > Brian
> > 
> > > Thanks,
> > > Gao Xiang
> > > 
> > > > 
> > > > Brian
> > > > 
> > > > >  int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
> > > > >  			struct xfs_ag_geometry *ageo);
> > > > >  
> > > > > -- 
> > > > > 2.27.0
> > > > > 
> > > > 
> > > 
> > 
>
diff mbox series

Patch

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index 9331f3516afa..1f6f9e70e1cb 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -22,6 +22,11 @@ 
 #include "xfs_ag.h"
 #include "xfs_ag_resv.h"
 #include "xfs_health.h"
+#include "xfs_error.h"
+#include "xfs_bmap.h"
+#include "xfs_defer.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
 
 static int
 xfs_get_aghdr_buf(
@@ -485,6 +490,112 @@  xfs_ag_init_headers(
 	return error;
 }
 
+int
+xfs_ag_shrink_space(
+	struct xfs_mount	*mp,
+	struct xfs_trans	**tpp,
+	xfs_agnumber_t		agno,
+	xfs_extlen_t		delta)
+{
+	struct xfs_alloc_arg	args = {
+		.tp	= *tpp,
+		.mp	= mp,
+		.type	= XFS_ALLOCTYPE_THIS_BNO,
+		.minlen = delta,
+		.maxlen = delta,
+		.oinfo	= XFS_RMAP_OINFO_SKIP_UPDATE,
+		.resv	= XFS_AG_RESV_NONE,
+		.prod	= 1
+	};
+	struct xfs_buf		*agibp, *agfbp;
+	struct xfs_agi		*agi;
+	struct xfs_agf		*agf;
+	int			error, err2;
+
+	ASSERT(agno == mp->m_sb.sb_agcount - 1);
+	error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
+	if (error)
+		return error;
+
+	agi = agibp->b_addr;
+
+	error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
+	if (error)
+		return error;
+
+	agf = agfbp->b_addr;
+	if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
+		return -EFSCORRUPTED;
+
+	if (delta >= agi->agi_length)
+		return -EINVAL;
+
+	args.fsbno = XFS_AGB_TO_FSB(mp, agno,
+				    be32_to_cpu(agi->agi_length) - delta);
+
+	/* remove the preallocations before allocation and re-establish then */
+	error = xfs_ag_resv_free(agibp->b_pag);
+	if (error)
+		return error;
+
+	/* internal log shouldn't also show up in the free space btrees */
+	error = xfs_alloc_vextent(&args);
+	if (!error && args.agbno == NULLAGBLOCK)
+		error = -ENOSPC;
+
+	if (error) {
+		/*
+		 * if extent allocation fails, need to roll the transaction to
+		 * ensure that the AGFL fixup has been committed anyway.
+		 */
+		err2 = xfs_trans_roll(tpp);
+		if (err2)
+			return err2;
+		goto resv_init_out;
+	}
+
+	/*
+	 * if successfully deleted from freespace btrees, need to confirm
+	 * per-AG reservation works as expected.
+	 */
+	be32_add_cpu(&agi->agi_length, -delta);
+	be32_add_cpu(&agf->agf_length, -delta);
+
+	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
+	if (err2) {
+		be32_add_cpu(&agi->agi_length, delta);
+		be32_add_cpu(&agf->agf_length, delta);
+		if (err2 != -ENOSPC)
+			goto resv_err;
+
+		__xfs_bmap_add_free(*tpp, args.fsbno, delta, NULL, true);
+
+		/*
+		 * Roll the transaction before trying to re-init the per-ag
+		 * reservation. The new transaction is clean so it will cancel
+		 * without any side effects.
+		 */
+		error = xfs_defer_finish(tpp);
+		if (error)
+			return error;
+
+		error = -ENOSPC;
+		goto resv_init_out;
+	}
+	xfs_ialloc_log_agi(*tpp, agibp, XFS_AGI_LENGTH);
+	xfs_alloc_log_agf(*tpp, agfbp, XFS_AGF_LENGTH);
+	return 0;
+
+resv_init_out:
+	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
+	if (!err2)
+		return error;
+resv_err:
+	xfs_warn(mp, "Error %d reserving per-AG metadata reserve pool.", err2);
+	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+	return err2;
+}
+
 /*
  * Extent the AG indicated by the @id by the length passed in
  */
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 5166322807e7..41293ebde8da 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -24,8 +24,10 @@  struct aghdr_init_data {
 };
 
 int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
+int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
+			xfs_agnumber_t agno, xfs_extlen_t len);
 int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
-			struct aghdr_init_data *id, xfs_extlen_t len);
+			struct aghdr_init_data *id, xfs_extlen_t delta);
 int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
 			struct xfs_ag_geometry *ageo);