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    Subject[PATCH 4.13 74/85] xfs: perag initialization should only touch m_ag_max_usable for AG 0
    Date
    4.13-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Darrick J. Wong <darrick.wong@oracle.com>

    commit 9789dd9e1d939232e8ff4c50ef8e75aa6781b3fb upstream.

    We call __xfs_ag_resv_init to make a per-AG reservation for each AG.
    This makes the reservation per-AG, not per-filesystem. Therefore, it
    is incorrect to adjust m_ag_max_usable for each AG. Adjust it only
    when we're reserving AG 0's blocks so that we only do it once per fs.

    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: Brian Foster <bfoster@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/xfs/libxfs/xfs_ag_resv.c | 12 ++++++++++--
    1 file changed, 10 insertions(+), 2 deletions(-)

    --- a/fs/xfs/libxfs/xfs_ag_resv.c
    +++ b/fs/xfs/libxfs/xfs_ag_resv.c
    @@ -156,7 +156,8 @@ __xfs_ag_resv_free(
    trace_xfs_ag_resv_free(pag, type, 0);

    resv = xfs_perag_resv(pag, type);
    - pag->pag_mount->m_ag_max_usable += resv->ar_asked;
    + if (pag->pag_agno == 0)
    + pag->pag_mount->m_ag_max_usable += resv->ar_asked;
    /*
    * AGFL blocks are always considered "free", so whatever
    * was reserved at mount time must be given back at umount.
    @@ -216,7 +217,14 @@ __xfs_ag_resv_init(
    return error;
    }

    - mp->m_ag_max_usable -= ask;
    + /*
    + * Reduce the maximum per-AG allocation length by however much we're
    + * trying to reserve for an AG. Since this is a filesystem-wide
    + * counter, we only make the adjustment for AG 0. This assumes that
    + * there aren't any AGs hungrier for per-AG reservation than AG 0.
    + */
    + if (pag->pag_agno == 0)
    + mp->m_ag_max_usable -= ask;

    resv = xfs_perag_resv(pag, type);
    resv->ar_asked = ask;

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