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

Darrick J. Wong
2023-02-01T19:28:59Z

On Thu, Jan 19, 2023 at 09:44:37AM +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))

This seems like a useful new iterator. I like that the opencoded loops
finally got cleaned up.

> +
> +
> 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

<snip>

> @@ -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;

Same question as Allison -- if xfs_bmap_longest_free_extent returned a
non-EAGAIN error code, don't we want to return that to the caller?

--D

> @@ -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;
> }
>
> /*
> --
> 2.39.0
>