Re: [PATCH 14/42] xfs: introduce xfs_for_each_perag_wrap()

Allison Henderson
2023-01-23T05:41:19Z

On Thu, 2023-01-19 at 09:44 +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> In several places we iterate every AG from a specific start agno and
> wrap back to the first AG when we reach the end of the filesystem to
> continue searching. We don't have a primitive for this iteration
> yet, so add one for conversion of these algorithms to per-ag based
> iteration.
>
> The filestream AG select code is a mess, and this initially makes it
> worse. The per-ag selection needs to be driven completely into the
> filestream code to clean this up and it will be done in a future
> patch that makes the filestream allocator use active per-ag
> references correctly.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_ag.h     | 45 +++++++++++++++++++++-
>  fs/xfs/libxfs/xfs_bmap.c   | 76 ++++++++++++++++++++++--------------
> --
>  fs/xfs/libxfs/xfs_ialloc.c | 32 ++++++++--------
>  3 files changed, 104 insertions(+), 49 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 187d30d9bb13..8f43b91d4cf3 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -237,7 +237,6 @@ xfs_perag_next(
>  #define for_each_perag_from(mp, agno, pag) \
>         for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount - 1,
> (pag))
>
> -
>  #define for_each_perag(mp, agno, pag) \
>         (agno) = 0; \
>         for_each_perag_from((mp), (agno), (pag))
> @@ -249,6 +248,50 @@ xfs_perag_next(
>                 xfs_perag_rele(pag), \
>                 (pag) = xfs_perag_grab_tag((mp), (agno), (tag)))
>
> +static inline struct xfs_perag *
> +xfs_perag_next_wrap(
> +       struct xfs_perag        *pag,
> +       xfs_agnumber_t          *agno,
> +       xfs_agnumber_t          stop_agno,
> +       xfs_agnumber_t          wrap_agno)
> +{
> +       struct xfs_mount        *mp = pag->pag_mount;
> +
> +       *agno = pag->pag_agno + 1;
> +       xfs_perag_rele(pag);
> +       while (*agno != stop_agno) {
> +               if (*agno >= wrap_agno)
> +                       *agno = 0;
> +               if (*agno == stop_agno)
> +                       break;
> +
> +               pag = xfs_perag_grab(mp, *agno);
> +               if (pag)
> +                       return pag;
> +               (*agno)++;
> +       }
> +       return NULL;
> +}
> +
> +/*
> + * Iterate all AGs from start_agno through wrap_agno, then 0 through
> + * (start_agno - 1).
> + */
> +#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag)
> \
> +       for ((agno) = (start_agno), (pag) = xfs_perag_grab((mp),
> (agno)); \
> +               (pag) != NULL; \
> +               (pag) = xfs_perag_next_wrap((pag), &(agno),
> (start_agno), \
> +                               (wrap_agno)))
> +
> +/*
> + * Iterate all AGs from start_agno through to the end of the
> filesystem, then 0
> + * through (start_agno - 1).
> + */
> +#define for_each_perag_wrap(mp, start_agno, agno, pag) \
> +       for_each_perag_wrap_at((mp), (start_agno), (mp)-
> >m_sb.sb_agcount, \
> +                               (agno), (pag))
> +
> +
>  struct aghdr_init_data {
>         /* per ag data */
>         xfs_agblock_t           agno;           /* ag to init */
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 6aad0ea5e606..e5519abbfa0d 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3136,17 +3136,14 @@ xfs_bmap_adjacent(
>
>  static int
>  xfs_bmap_longest_free_extent(
> +       struct xfs_perag        *pag,
>         struct xfs_trans        *tp,
> -       xfs_agnumber_t          ag,
>         xfs_extlen_t            *blen,
>         int                     *notinit)
>  {
> -       struct xfs_mount        *mp = tp->t_mountp;
> -       struct xfs_perag        *pag;
>         xfs_extlen_t            longest;
>         int                     error = 0;
>
> -       pag = xfs_perag_get(mp, ag);
>         if (!xfs_perag_initialised_agf(pag)) {
>                 error = xfs_alloc_read_agf(pag, tp,
> XFS_ALLOC_FLAG_TRYLOCK,
>                                 NULL);
> @@ -3156,19 +3153,17 @@ xfs_bmap_longest_free_extent(
>                                 *notinit = 1;
>                                 error = 0;
>                         }
> -                       goto out;
> +                       return error;
>                 }
>         }
>
>         longest = xfs_alloc_longest_free_extent(pag,
> -                               xfs_alloc_min_freelist(mp, pag),
> +                               xfs_alloc_min_freelist(pag-
> >pag_mount, pag),
>                                 xfs_ag_resv_needed(pag,
> XFS_AG_RESV_NONE));
>         if (*blen < longest)
>                 *blen = longest;
>
> -out:
> -       xfs_perag_put(pag);
> -       return error;
> +       return 0;
>  }
>
>  static void
> @@ -3206,9 +3201,10 @@ xfs_bmap_btalloc_select_lengths(
>         xfs_extlen_t            *blen)
>  {
>         struct xfs_mount        *mp = ap->ip->i_mount;
> -       xfs_agnumber_t          ag, startag;
> +       struct xfs_perag        *pag;
> +       xfs_agnumber_t          agno, startag;
>         int                     notinit = 0;
> -       int                     error;
> +       int                     error = 0;
>
>         args->type = XFS_ALLOCTYPE_START_BNO;
>         if (ap->tp->t_flags & XFS_TRANS_LOWMODE) {
> @@ -3218,21 +3214,21 @@ xfs_bmap_btalloc_select_lengths(
>         }
>
>         args->total = ap->total;
> -       startag = ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
> +       startag = XFS_FSB_TO_AGNO(mp, args->fsbno);
>         if (startag == NULLAGNUMBER)
> -               startag = ag = 0;
> +               startag = 0;
>
> -       while (*blen < args->maxlen) {
> -               error = xfs_bmap_longest_free_extent(args->tp, ag,
> blen,
> +       *blen = 0;
> +       for_each_perag_wrap(mp, startag, agno, pag) {
> +               error = xfs_bmap_longest_free_extent(pag, args->tp,
> blen,
>                                                      &notinit);
>                 if (error)
> -                       return error;
> -
> -               if (++ag == mp->m_sb.sb_agcount)
> -                       ag = 0;
> -               if (ag == startag)
> +                       break;
> +               if (*blen >= args->maxlen)
>                         break;
>         }
> +       if (pag)
> +               xfs_perag_rele(pag);
>
>         xfs_bmap_select_minlen(ap, args, blen, notinit);
>         return 0;
Hmm, did you want to return error here? Since now we only break on
error in the loop body above?

Otherwise looks good.
Allison

> @@ -3245,7 +3241,8 @@ xfs_bmap_btalloc_filestreams(
>         xfs_extlen_t            *blen)
>  {
>         struct xfs_mount        *mp = ap->ip->i_mount;
> -       xfs_agnumber_t          ag;
> +       struct xfs_perag        *pag;
> +       xfs_agnumber_t          start_agno;
>         int                     notinit = 0;
>         int                     error;
>
> @@ -3259,33 +3256,50 @@ xfs_bmap_btalloc_filestreams(
>         args->type = XFS_ALLOCTYPE_NEAR_BNO;
>         args->total = ap->total;
>
> -       ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
> -       if (ag == NULLAGNUMBER)
> -               ag = 0;
> +       start_agno = XFS_FSB_TO_AGNO(mp, args->fsbno);
> +       if (start_agno == NULLAGNUMBER)
> +               start_agno = 0;
>
> -       error = xfs_bmap_longest_free_extent(args->tp, ag, blen,
> &notinit);
> -       if (error)
> -               return error;
> +       pag = xfs_perag_grab(mp, start_agno);
> +       if (pag) {
> +               error = xfs_bmap_longest_free_extent(pag, args->tp,
> blen,
> +                               &notinit);
> +               xfs_perag_rele(pag);
> +               if (error)
> +                       return error;
> +       }
>
>         if (*blen < args->maxlen) {
> -               error = xfs_filestream_new_ag(ap, &ag);
> +               xfs_agnumber_t  agno = start_agno;
> +
> +               error = xfs_filestream_new_ag(ap, &agno);
>                 if (error)
>                         return error;
> +               if (agno == NULLAGNUMBER)
> +                       goto out_select;
>
> -               error = xfs_bmap_longest_free_extent(args->tp, ag,
> blen,
> -                                                    &notinit);
> +               pag = xfs_perag_grab(mp, agno);
> +               if (!pag)
> +                       goto out_select;
> +
> +               error = xfs_bmap_longest_free_extent(pag, args->tp,
> +                               blen, &notinit);
> +               xfs_perag_rele(pag);
>                 if (error)
>                         return error;
>
> +               start_agno = agno;
> +
>         }
>
> +out_select:
>         xfs_bmap_select_minlen(ap, args, blen, notinit);
>
>         /*
>          * Set the failure fallback case to look in the selected AG
> as stream
>          * may have moved.
>          */
> -       ap->blkno = args->fsbno = XFS_AGB_TO_FSB(mp, ag, 0);
> +       ap->blkno = args->fsbno = XFS_AGB_TO_FSB(mp, start_agno, 0);
>         return 0;
>  }
>
> diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> index 2a323ffa5ba9..50fef3f5af51 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.c
> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> @@ -1725,7 +1725,7 @@ xfs_dialloc(
>         bool                    ok_alloc = true;
>         bool                    low_space = false;
>         int                     flags;
> -       xfs_ino_t               ino;
> +       xfs_ino_t               ino = NULLFSINO;
>
>         /*
>          * Directories, symlinks, and regular files frequently
> allocate at least
> @@ -1773,39 +1773,37 @@ xfs_dialloc(
>          * or in which we can allocate some inodes.  Iterate through
> the
>          * allocation groups upward, wrapping at the end.
>          */
> -       agno = start_agno;
>         flags = XFS_ALLOC_FLAG_TRYLOCK;
> -       for (;;) {
> -               pag = xfs_perag_grab(mp, agno);
> +retry:
> +       for_each_perag_wrap_at(mp, start_agno, mp->m_maxagi, agno,
> pag) {
>                 if (xfs_dialloc_good_ag(pag, *tpp, mode, flags,
> ok_alloc)) {
>                         error = xfs_dialloc_try_ag(pag, tpp, parent,
>                                         &ino, ok_alloc);
>                         if (error != -EAGAIN)
>                                 break;
> +                       error = 0;
>                 }
>
>                 if (xfs_is_shutdown(mp)) {
>                         error = -EFSCORRUPTED;
>                         break;
>                 }
> -               if (++agno == mp->m_maxagi)
> -                       agno = 0;
> -               if (agno == start_agno) {
> -                       if (!flags) {
> -                               error = -ENOSPC;
> -                               break;
> -                       }
> +       }
> +       if (pag)
> +               xfs_perag_rele(pag);
> +       if (error)
> +               return error;
> +       if (ino == NULLFSINO) {
> +               if (flags) {
>                         flags = 0;
>                         if (low_space)
>                                 ok_alloc = true;
> +                       goto retry;
>                 }
> -               xfs_perag_rele(pag);
> +               return -ENOSPC;
>         }
> -
> -       if (!error)
> -               *new_ino = ino;
> -       xfs_perag_rele(pag);
> -       return error;
> +       *new_ino = ino;
> +       return 0;
>  }
>
>  /*