Re: [PATCH 21/22] xfs: clean up and simplify xfs_dialloc()

Darrick J. Wong
2021-05-12T22:42:14Z

On Thu, May 06, 2021 at 05:20:53PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Because it's a mess.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_ialloc.c | 270 +++++++++++++++++++++----------------
> 1 file changed, 153 insertions(+), 117 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> index d749bb7c7a69..340bb95d7bc1 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.c
> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> @@ -604,9 +604,10 @@ xfs_inobt_insert_sprec(
> }
>
> /*
> - * Allocate new inodes in the allocation group specified by agbp.
> - * Returns 0 if inodes were allocated in this AG; 1 if there was no space
> - * in this AG; or the usual negative error code.
> + * Allocate new inodes in the allocation group specified by agbp. Returns 0 if
> + * inodes were allocated in this AG; -EAGAIN if there was no space in this AG so
> + * the caller knows it can try another AG, a hard -ENOSPC when over the maximum
> + * inode count threshold, or the usual negative error code for other errors.
> */
> STATIC int
> xfs_ialloc_ag_alloc(
> @@ -792,7 +793,7 @@ xfs_ialloc_ag_alloc(
> }
>
> if (args.fsbno == NULLFSBLOCK)
> - return 1;
> + return -EAGAIN;
>
> ASSERT(args.len == args.minlen);
>
> @@ -1568,14 +1569,17 @@ xfs_dialloc_roll(
> /* Re-attach the quota info that we detached from prev trx. */
> tp->t_dqinfo = dqinfo;
>
> - *tpp = tp;
> - if (error)
> - return error;
> + /*
> + * Join the buffer even on commit error so that the buffer is released
> + * when the caller cancels the transaction and doesn't have to handle
> + * this error case specially.
> + */
> xfs_trans_bjoin(tp, agibp);
> - return 0;
> + *tpp = tp;
> + return error;
> }
>
> -STATIC xfs_agnumber_t
> +static xfs_agnumber_t
> xfs_ialloc_next_ag(
> xfs_mount_t *mp)
> {
> @@ -1590,16 +1594,136 @@ xfs_ialloc_next_ag(
> return agno;
> }
>
> +static bool
> +xfs_dialloc_good_ag(
> + struct xfs_trans *tp,
> + struct xfs_perag *pag,
> + umode_t mode,
> + int flags,
> + bool ok_alloc)
> +{
> + struct xfs_mount *mp = tp->t_mountp;
> + xfs_extlen_t ineed;
> + xfs_extlen_t longest = 0;
> + int needspace;
> + int error;
> +
> + if (!pag->pagi_inodeok)
> + return false;
> +
> + if (!pag->pagi_init) {
> + error = xfs_ialloc_pagi_init(mp, tp, pag->pag_agno);
> + if (error)
> + return false;
> + }
> +
> + if (pag->pagi_freecount)
> + return true;
> + if (!ok_alloc)
> + return false;
> +
> + if (!pag->pagf_init) {
> + error = xfs_alloc_pagf_init(mp, tp, pag->pag_agno, flags);
> + if (error)
> + return false;
> + }
> +
> + /*
> + * Check that there is enough free space for the file plus a chunk of
> + * inodes if we need to allocate some. If this is the first pass across
> + * the AGs, take into account the potential space needed for alignment
> + * of inode chunks when checking the longest contiguous free space in
> + * the AG - this prevents us from getting ENOSPC because we have free
> + * space larger than ialloc_blks but alignment constraints prevent us
> + * from using it.
> + *
> + * If we can't find an AG with space for full alignment slack to be
> + * taken into account, we must be near ENOSPC in all AGs. Hence we
> + * don't include alignment for the second pass and so if we fail
> + * allocation due to alignment issues then it is most likely a real
> + * ENOSPC condition.
> + *
> + * XXX(dgc): this calculation is now bogus thanks to the per-ag
> + * reservations that xfs_alloc_fix_freelist() now does via
> + * xfs_alloc_space_available(). When the AG fills up, pagf_freeblks will
> + * be more than large enough for the check below to succeed, but
> + * xfs_alloc_space_available() will fail because of the non-zero
> + * metadata reservation and hence we won't actually be able to allocate
> + * more inodes in this AG. We do soooo much unnecessary work near ENOSPC
> + * because of this.

Yuck. Can this be fixed by doing:

really_free = pag->pagf_freeblks -
xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE);
return really_free >= needspace + ineed && longest >= ineed)

to account for those reservations, perhaps?

> + */
> + ineed = M_IGEO(mp)->ialloc_min_blks;
> + if (flags && ineed > 1)
> + ineed += M_IGEO(mp)->cluster_align;
> + longest = pag->pagf_longest;
> + if (!longest)
> + longest = pag->pagf_flcount > 0;
> + needspace = S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode);
> +
> + if (pag->pagf_freeblks < needspace + ineed || longest < ineed)
> + return false;
> + return true;
> +}
> +
> +static int
> +xfs_dialloc_try_ag(
> + struct xfs_trans **tpp,
> + struct xfs_perag *pag,
> + xfs_ino_t parent,
> + xfs_ino_t *new_ino,
> + bool ok_alloc)
> +{
> + struct xfs_buf *agbp;
> + xfs_ino_t ino;
> + int error;
> +
> + /*
> + * Then read in the AGI buffer and recheck with the AGI buffer
> + * lock held.
> + */
> + error = xfs_ialloc_read_agi(pag->pag_mount, *tpp, pag->pag_agno, &agbp);
> + if (error)
> + return error;
> +
> + if (!pag->pagi_freecount) {
> + if (!ok_alloc) {
> + error = -EAGAIN;
> + goto out_release;
> + }
> +
> + error = xfs_ialloc_ag_alloc(*tpp, agbp, pag);
> + if (error < 0)
> + goto out_release;
> +
> + /*
> + * We successfully allocated space for an inode cluster in this
> + * AG. Roll the transaction so that we can allocate one of the
> + * new inodes.
> + */
> + ASSERT(pag->pagi_freecount > 0);
> + error = xfs_dialloc_roll(tpp, agbp);
> + if (error)
> + goto out_release;
> + }
> +
> + /* Allocate an inode in the found AG */
> + error = xfs_dialloc_ag(*tpp, agbp, pag, parent, &ino);
> + if (!error)
> + *new_ino = ino;
> + return error;
> +
> +out_release:
> + xfs_trans_brelse(*tpp, agbp);
> + return error;
> +}
> +
> /*
> - * Select and prepare an AG for inode allocation.
> + * Allocate an on-disk inode.
> *
> * Mode is used to tell whether the new inode is a directory and hence where to
> - * locate it.
> - *
> - * This function will ensure that the selected AG has free inodes available to
> - * allocate from. The selected AGI will be returned locked to the caller, and it
> - * will allocate more free inodes if required. If no free inodes are found or
> - * can be allocated, -ENOSPC be returned.
> + * locate it. The on-disk inode that is allocated will be returned in @new_ino
> + * on success, otherwise an error will be set to indicate the failure (e.g.
> + * -ENOSPC).
> */
> int
> xfs_dialloc(
> @@ -1609,14 +1733,12 @@ xfs_dialloc(
> xfs_ino_t *new_ino)
> {
> struct xfs_mount *mp = (*tpp)->t_mountp;
> - struct xfs_buf *agbp;
> xfs_agnumber_t agno;
> int error = 0;
> xfs_agnumber_t start_agno;
> struct xfs_perag *pag;
> struct xfs_ino_geometry *igeo = M_IGEO(mp);
> - bool okalloc = true;
> - int needspace;
> + bool ok_alloc = true;
> int flags;
> xfs_ino_t ino;
>
> @@ -1624,7 +1746,6 @@ xfs_dialloc(
> * Files of these types need at least one block if length > 0
> * (and they won't fit in the inode, but that's hard to figure out).
> */
> - needspace = S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode);
> if (S_ISDIR(mode))
> start_agno = xfs_ialloc_next_ag(mp);
> else {
> @@ -1635,7 +1756,7 @@ xfs_dialloc(
>
> /*
> * If we have already hit the ceiling of inode blocks then clear
> - * okalloc so we scan all available agi structures for a free
> + * ok_alloc so we scan all available agi structures for a free
> * inode.
> *
> * Read rough value of mp->m_icount by percpu_counter_read_positive,
> @@ -1644,7 +1765,7 @@ xfs_dialloc(

Er... didn't this logic get split into xfs_dialloc_select_ag in 5.11?

Nice cleanup, at least...

--D

> if (igeo->maxicount &&
> percpu_counter_read_positive(&mp->m_icount) + igeo->ialloc_inos
> > igeo->maxicount) {
> - okalloc = false;
> + ok_alloc = false;
> }
>
> /*
> @@ -1655,95 +1776,14 @@ xfs_dialloc(
> agno = start_agno;
> flags = XFS_ALLOC_FLAG_TRYLOCK;
> for (;;) {
> - xfs_extlen_t ineed;
> - xfs_extlen_t longest = 0;
> -
> pag = xfs_perag_get(mp, agno);
> - if (!pag->pagi_inodeok)
> - goto nextag;
> -
> - if (!pag->pagi_init) {
> - error = xfs_ialloc_pagi_init(mp, *tpp, agno);
> - if (error)
> - break;
> - }
> -
> - if (!pag->pagi_freecount)
> - goto nextag;
> - if (!okalloc)
> - goto nextag;
> -
> - if (!pag->pagf_init) {
> - error = xfs_alloc_pagf_init(mp, *tpp, agno, flags);
> - if (error)
> - goto nextag;
> - }
> -
> - /*
> - * Check that there is enough free space for the file plus a
> - * chunk of inodes if we need to allocate some. If this is the
> - * first pass across the AGs, take into account the potential
> - * space needed for alignment of inode chunks when checking the
> - * longest contiguous free space in the AG - this prevents us
> - * from getting ENOSPC because we have free space larger than
> - * ialloc_blks but alignment constraints prevent us from using
> - * it.
> - *
> - * If we can't find an AG with space for full alignment slack to
> - * be taken into account, we must be near ENOSPC in all AGs.
> - * Hence we don't include alignment for the second pass and so
> - * if we fail allocation due to alignment issues then it is most
> - * likely a real ENOSPC condition.
> - */
> - ineed = M_IGEO(mp)->ialloc_min_blks;
> - if (flags && ineed > 1)
> - ineed += M_IGEO(mp)->cluster_align;
> - longest = pag->pagf_longest;
> - if (!longest)
> - longest = pag->pagf_flcount > 0;
> -
> - if (pag->pagf_freeblks < needspace + ineed || longest < ineed)
> - goto nextag;
> -
> - /*
> - * Then read in the AGI buffer and recheck with the AGI buffer
> - * lock held.
> - */
> - error = xfs_ialloc_read_agi(mp, *tpp, agno, &agbp);
> - if (error)
> - break;
> -
> - if (pag->pagi_freecount)
> - goto found_ag;
> -
> - if (!okalloc)
> - goto nextag_relse_buffer;
> -
> - error = xfs_ialloc_ag_alloc(*tpp, agbp, pag);
> - if (error < 0) {
> - xfs_trans_brelse(*tpp, agbp);
> - break;
> - }
> -
> - if (error == 0) {
> - /*
> - * We successfully allocated space for an inode cluster
> - * in this AG. Roll the transaction so that we can
> - * allocate one of the new inodes.
> - */
> - ASSERT(pag->pagi_freecount > 0);
> -
> - error = xfs_dialloc_roll(tpp, agbp);
> - if (error) {
> - xfs_buf_relse(agbp);
> + if (xfs_dialloc_good_ag(*tpp, pag, mode, flags, ok_alloc)) {
> + error = xfs_dialloc_try_ag(tpp, pag, parent,
> + &ino, ok_alloc);
> + if (error != -EAGAIN)
> break;
> - }
> - goto found_ag;
> }
>
> -nextag_relse_buffer:
> - xfs_trans_brelse(*tpp, agbp);
> -nextag:
> if (XFS_FORCED_SHUTDOWN(mp)) {
> error = -EFSCORRUPTED;
> break;
> @@ -1751,23 +1791,19 @@ xfs_dialloc(
> if (++agno == mp->m_maxagi)
> agno = 0;
> if (agno == start_agno) {
> - if (!flags)
> + if (!flags) {
> + error = -ENOSPC;
> break;
> + }
> flags = 0;
> }
> xfs_perag_put(pag);
> }
>
> + if (!error)
> + *new_ino = ino;
> xfs_perag_put(pag);
> - return error ? error : -ENOSPC;
> -found_ag:
> - /* Allocate an inode in the found AG */
> - error = xfs_dialloc_ag(*tpp, agbp, pag, parent, &ino);
> - xfs_perag_put(pag);
> - if (error)
> - return error;
> - *new_ino = ino;
> - return 0;
> + return error;
> }
>
> /*
> --
> 2.31.1
>