Re: [PATCH v3 1/2] xfs: set a mount flag when perag reservation is active

Darrick J. Wong
2021-04-14T00:49:54Z

On Mon, Apr 12, 2021 at 09:30:58AM -0400, Brian Foster wrote:
> perag reservation is enabled at mount time on a per AG basis. The
> upcoming in-core allocation btree accounting mechanism needs to know
> when reservation is enabled and that all perag AGF contexts are
> initialized. As a preparation step, set a flag in the mount
> structure and unconditionally initialize the pagf on all mounts
> where at least one reservation is active.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
> fs/xfs/libxfs/xfs_ag_resv.c | 24 ++++++++++++++----------
> fs/xfs/xfs_mount.h | 1 +
> 2 files changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
> index 6c5f8d10589c..9b2fc4abad2c 100644
> --- a/fs/xfs/libxfs/xfs_ag_resv.c
> +++ b/fs/xfs/libxfs/xfs_ag_resv.c
> @@ -254,6 +254,7 @@ xfs_ag_resv_init(
> xfs_extlen_t ask;
> xfs_extlen_t used;
> int error = 0;
> + bool has_resv = false;
>
> /* Create the metadata reservation. */
> if (pag->pag_meta_resv.ar_asked == 0) {
> @@ -291,6 +292,8 @@ xfs_ag_resv_init(
> if (error)
> goto out;
> }
> + if (ask)
> + has_resv = true;
> }
>
> /* Create the RMAPBT metadata reservation */
> @@ -304,18 +307,19 @@ xfs_ag_resv_init(
> error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
> if (error)
> goto out;
> + if (ask)
> + has_resv = true;
> }
>
> -#ifdef DEBUG
> - /* need to read in the AGF for the ASSERT below to work */
> - error = xfs_alloc_pagf_init(pag->pag_mount, tp, pag->pag_agno, 0);
> - if (error)
> - return error;
> -
> - ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
> - xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <=
> - pag->pagf_freeblks + pag->pagf_flcount);
> -#endif
> + if (has_resv) {
> + mp->m_has_agresv = true;

If the metadata reservation succeeds but the rmapbt reservation fails
with ENOSPC, won't we fail to set m_has_agresv true here? We don't fail
the entire mount if ENOSPC happens, which means that there's a slight
chance of doing the wrong thing here if all the AGs are (somehow) like
that.

--D

> + error = xfs_alloc_pagf_init(mp, tp, pag->pag_agno, 0);
> + if (error)
> + return error;
> + ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
> + xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <=
> + pag->pagf_freeblks + pag->pagf_flcount);
> + }
> out:
> return error;
> }
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 81829d19596e..8847ffd29777 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -139,6 +139,7 @@ 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 */
> + bool m_has_agresv; /* perag reservations active */
>
> /*
> * Bitsets of per-fs metadata that have been checked and/or are sick.
> --
> 2.26.3
>