Re: [PATCH 13/45] xfs: xfs_log_force_lsn isn't passed a LSN

Darrick J. Wong
2021-03-08T22:54:25Z

On Fri, Mar 05, 2021 at 04:11:11PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> In doing an investigation into AIL push stalls, I was looking at the
> log force code to see if an async CIL push could be done instead.
> This lead me to xfs_log_force_lsn() and looking at how it works.
>
> xfs_log_force_lsn() is only called from inode synchronisation
> contexts such as fsync(), and it takes the ip->i_itemp->ili_last_lsn
> value as the LSN to sync the log to. This gets passed to
> xlog_cil_force_lsn() via xfs_log_force_lsn() to flush the CIL to the
> journal, and then used by xfs_log_force_lsn() to flush the iclogs to
> the journal.
>
> The problem with is that ip->i_itemp->ili_last_lsn does not store a
> log sequence number. What it stores is passed to it from the
> ->iop_committing method, which is called by xfs_log_commit_cil().
> The value this passes to the iop_committing method is the CIL
> context sequence number that the item was committed to.
>
> As it turns out, xlog_cil_force_lsn() converts the sequence to an
> actual commit LSN for the related context and returns that to
> xfs_log_force_lsn(). xfs_log_force_lsn() overwrites it's "lsn"
> variable that contained a sequence with an actual LSN and then uses
> that to sync the iclogs.
>
> This caused me some confusion for a while, even though I originally
> wrote all this code a decade ago. ->iop_committing is only used by
> a couple of log item types, and only inode items use the sequence
> number it is passed.
>
> Let's clean up the API, CIL structures and inode log item to call it
> a sequence number, and make it clear that the high level code is
> using CIL sequence numbers and not on-disk LSNs for integrity
> synchronisation purposes.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_types.h | 1 +
> fs/xfs/xfs_buf_item.c | 2 +-
> fs/xfs/xfs_dquot_item.c | 2 +-
> fs/xfs/xfs_file.c | 14 +++++++-------
> fs/xfs/xfs_inode.c | 10 +++++-----
> fs/xfs/xfs_inode_item.c | 4 ++--
> fs/xfs/xfs_inode_item.h | 2 +-
> fs/xfs/xfs_log.c | 27 ++++++++++++++-------------
> fs/xfs/xfs_log.h | 4 +---
> fs/xfs/xfs_log_cil.c | 22 +++++++++-------------
> fs/xfs/xfs_log_priv.h | 15 +++++++--------
> fs/xfs/xfs_trans.c | 6 +++---
> fs/xfs/xfs_trans.h | 4 ++--
> 13 files changed, 54 insertions(+), 59 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h
> index 064bd6e8c922..0870ef6f933d 100644
> --- a/fs/xfs/libxfs/xfs_types.h
> +++ b/fs/xfs/libxfs/xfs_types.h
> @@ -21,6 +21,7 @@ typedef int32_t xfs_suminfo_t; /* type of bitmap summary info */
> typedef uint32_t xfs_rtword_t; /* word type for bitmap manipulations */
>
> typedef int64_t xfs_lsn_t; /* log sequence number */
> +typedef int64_t xfs_csn_t; /* CIL sequence number */

I'm unfamiliar with the internal format of CIL sequence numbers. Do
they have the same cycle:offset segmented structure as LSNs do? Or are
they a simple linear integer that increases as we checkpoint committed
items?

Looking through the current code, I see a couple of places where we
initialize them to 1, and I also see that when we create a new cil
context we set its sequence to one more than the context that it will
replace.

I also see a bunch of comparisons of cil context sequence numbers that
use standard integer operators, but then I also see one instance of:

if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
return false;
return true

in xfs_log_item_in_current_chkpt. AFAICT this could be replaced with a
simple:

return lip->li_seq == ctx->sequence;

But the fact that we're using LSN_CMP in /one/ place sticks out like a
sore thumb to me, and now I'm confused. Is my understanding incorrect,
or is this operator use incorrect?

> typedef uint32_t xfs_dablk_t; /* dir/attr block number (in file) */
> typedef uint32_t xfs_dahash_t; /* dir/attr hash value */
> diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> index 14d1fefcbf4c..1cb087b320b1 100644
> --- a/fs/xfs/xfs_buf_item.c
> +++ b/fs/xfs/xfs_buf_item.c
> @@ -713,7 +713,7 @@ xfs_buf_item_release(
> STATIC void
> xfs_buf_item_committing(
> struct xfs_log_item *lip,
> - xfs_lsn_t commit_lsn)
> + xfs_csn_t seq)
> {
> return xfs_buf_item_release(lip);
> }
> diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
> index 8c1fdf37ee8f..8ed47b739b6c 100644
> --- a/fs/xfs/xfs_dquot_item.c
> +++ b/fs/xfs/xfs_dquot_item.c
> @@ -188,7 +188,7 @@ xfs_qm_dquot_logitem_release(
> STATIC void
> xfs_qm_dquot_logitem_committing(
> struct xfs_log_item *lip,
> - xfs_lsn_t commit_lsn)
> + xfs_csn_t seq)
> {
> return xfs_qm_dquot_logitem_release(lip);

Weird, I didn't know that you could use return like this -- both
_release and _committing return void.

--D

> }
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 24c7f45fc4eb..ac3120dfe477 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -119,8 +119,8 @@ xfs_dir_fsync(
> return xfs_log_force_inode(ip);
> }
>
> -static xfs_lsn_t
> -xfs_fsync_lsn(
> +static xfs_csn_t
> +xfs_fsync_seq(
> struct xfs_inode *ip,
> bool datasync)
> {
> @@ -128,7 +128,7 @@ xfs_fsync_lsn(
> return 0;
> if (datasync && !(ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> return 0;
> - return ip->i_itemp->ili_last_lsn;
> + return ip->i_itemp->ili_commit_seq;
> }
>
> /*
> @@ -151,12 +151,12 @@ xfs_fsync_flush_log(
> int *log_flushed)
> {
> int error = 0;
> - xfs_lsn_t lsn;
> + xfs_csn_t seq;
>
> xfs_ilock(ip, XFS_ILOCK_SHARED);
> - lsn = xfs_fsync_lsn(ip, datasync);
> - if (lsn) {
> - error = xfs_log_force_lsn(ip->i_mount, lsn, XFS_LOG_SYNC,
> + seq = xfs_fsync_seq(ip, datasync);
> + if (seq) {
> + error = xfs_log_force_seq(ip->i_mount, seq, XFS_LOG_SYNC,
> log_flushed);
>
> spin_lock(&ip->i_itemp->ili_lock);
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index bed2beb169e4..1c2ef1f1859a 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2644,7 +2644,7 @@ xfs_iunpin(
> trace_xfs_inode_unpin_nowait(ip, _RET_IP_);
>
> /* Give the log a push to start the unpinning I/O */
> - xfs_log_force_lsn(ip->i_mount, ip->i_itemp->ili_last_lsn, 0, NULL);
> + xfs_log_force_seq(ip->i_mount, ip->i_itemp->ili_commit_seq, 0, NULL);
>
> }
>
> @@ -3652,16 +3652,16 @@ int
> xfs_log_force_inode(
> struct xfs_inode *ip)
> {
> - xfs_lsn_t lsn = 0;
> + xfs_csn_t seq = 0;
>
> xfs_ilock(ip, XFS_ILOCK_SHARED);
> if (xfs_ipincount(ip))
> - lsn = ip->i_itemp->ili_last_lsn;
> + seq = ip->i_itemp->ili_commit_seq;
> xfs_iunlock(ip, XFS_ILOCK_SHARED);
>
> - if (!lsn)
> + if (!seq)
> return 0;
> - return xfs_log_force_lsn(ip->i_mount, lsn, XFS_LOG_SYNC, NULL);
> + return xfs_log_force_seq(ip->i_mount, seq, XFS_LOG_SYNC, NULL);
> }
>
> /*
> diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
> index 6ff91e5bf3cd..3aba4559469f 100644
> --- a/fs/xfs/xfs_inode_item.c
> +++ b/fs/xfs/xfs_inode_item.c
> @@ -617,9 +617,9 @@ xfs_inode_item_committed(
> STATIC void
> xfs_inode_item_committing(
> struct xfs_log_item *lip,
> - xfs_lsn_t commit_lsn)
> + xfs_csn_t seq)
> {
> - INODE_ITEM(lip)->ili_last_lsn = commit_lsn;
> + INODE_ITEM(lip)->ili_commit_seq = seq;
> return xfs_inode_item_release(lip);
> }
>
> diff --git a/fs/xfs/xfs_inode_item.h b/fs/xfs/xfs_inode_item.h
> index 4b926e32831c..403b45ab9aa2 100644
> --- a/fs/xfs/xfs_inode_item.h
> +++ b/fs/xfs/xfs_inode_item.h
> @@ -33,7 +33,7 @@ struct xfs_inode_log_item {
> unsigned int ili_fields; /* fields to be logged */
> unsigned int ili_fsync_fields; /* logged since last fsync */
> xfs_lsn_t ili_flush_lsn; /* lsn at last flush */
> - xfs_lsn_t ili_last_lsn; /* lsn at last transaction */
> + xfs_csn_t ili_commit_seq; /* last transaction commit */
> };
>
> static inline int xfs_inode_clean(struct xfs_inode *ip)
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index ed44d67d7099..145db0f88060 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -3273,14 +3273,13 @@ xfs_log_force(
> }
>
> static int
> -__xfs_log_force_lsn(
> - struct xfs_mount *mp,
> +xlog_force_lsn(
> + struct xlog *log,
> xfs_lsn_t lsn,
> uint flags,
> int *log_flushed,
> bool already_slept)
> {
> - struct xlog *log = mp->m_log;
> struct xlog_in_core *iclog;
>
> spin_lock(&log->l_icloglock);
> @@ -3313,8 +3312,6 @@ __xfs_log_force_lsn(
> if (!already_slept &&
> (iclog->ic_prev->ic_state == XLOG_STATE_WANT_SYNC ||
> iclog->ic_prev->ic_state == XLOG_STATE_SYNCING)) {
> - XFS_STATS_INC(mp, xs_log_force_sleep);
> -
> xlog_wait(&iclog->ic_prev->ic_write_wait,
> &log->l_icloglock);
> return -EAGAIN;
> @@ -3352,25 +3349,29 @@ __xfs_log_force_lsn(
> * to disk, that thread will wake up all threads waiting on the queue.
> */
> int
> -xfs_log_force_lsn(
> +xfs_log_force_seq(
> struct xfs_mount *mp,
> - xfs_lsn_t lsn,
> + xfs_csn_t seq,
> uint flags,
> int *log_flushed)
> {
> + struct xlog *log = mp->m_log;
> + xfs_lsn_t lsn;
> int ret;
> - ASSERT(lsn != 0);
> + ASSERT(seq != 0);
>
> XFS_STATS_INC(mp, xs_log_force);
> - trace_xfs_log_force(mp, lsn, _RET_IP_);
> + trace_xfs_log_force(mp, seq, _RET_IP_);
>
> - lsn = xlog_cil_force_lsn(mp->m_log, lsn);
> + lsn = xlog_cil_force_seq(log, seq);
> if (lsn == NULLCOMMITLSN)
> return 0;
>
> - ret = __xfs_log_force_lsn(mp, lsn, flags, log_flushed, false);
> - if (ret == -EAGAIN)
> - ret = __xfs_log_force_lsn(mp, lsn, flags, log_flushed, true);
> + ret = xlog_force_lsn(log, lsn, flags, log_flushed, false);
> + if (ret == -EAGAIN) {
> + XFS_STATS_INC(mp, xs_log_force_sleep);
> + ret = xlog_force_lsn(log, lsn, flags, log_flushed, true);
> + }
> return ret;
> }
>
> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
> index 044e02cb8921..ba96f4ad9576 100644
> --- a/fs/xfs/xfs_log.h
> +++ b/fs/xfs/xfs_log.h
> @@ -107,7 +106,7 @@ struct xfs_item_ops;
> struct xfs_trans;
>
> int xfs_log_force(struct xfs_mount *mp, uint flags);
> -int xfs_log_force_lsn(struct xfs_mount *mp, xfs_lsn_t lsn, uint flags,
> +int xfs_log_force_seq(struct xfs_mount *mp, xfs_csn_t seq, uint flags,
> int *log_forced);
> int xfs_log_mount(struct xfs_mount *mp,
> struct xfs_buftarg *log_target,
> @@ -132,8 +132,6 @@ bool xfs_log_writable(struct xfs_mount *mp);
> struct xlog_ticket *xfs_log_ticket_get(struct xlog_ticket *ticket);
> void xfs_log_ticket_put(struct xlog_ticket *ticket);
>
> -void xfs_log_commit_cil(struct xfs_mount *mp, struct xfs_trans *tp,
> - xfs_lsn_t *commit_lsn, bool regrant);
> void xlog_cil_process_committed(struct list_head *list);
> bool xfs_log_item_in_current_chkpt(struct xfs_log_item *lip);
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 2f0adc35d8ec..44bb7cc17541 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -794,7 +794,7 @@ xlog_cil_push_work(
> * that higher sequences will wait for us to write out a commit record
> * before they do.
> *
> - * xfs_log_force_lsn requires us to mirror the new sequence into the cil
> + * xfs_log_force_seq requires us to mirror the new sequence into the cil
> * structure atomically with the addition of this sequence to the
> * committing list. This also ensures that we can do unlocked checks
> * against the current sequence in log forces without risking
> @@ -1058,16 +1058,14 @@ xlog_cil_empty(
> * allowed again.
> */
> void
> -xfs_log_commit_cil(
> - struct xfs_mount *mp,
> +xlog_cil_commit(
> + struct xlog *log,
> struct xfs_trans *tp,
> - xfs_lsn_t *commit_lsn,
> + xfs_csn_t *commit_seq,
> bool regrant)
> {
> - struct xlog *log = mp->m_log;
> struct xfs_cil *cil = log->l_cilp;
> struct xfs_log_item *lip, *next;
> - xfs_lsn_t xc_commit_lsn;
>
> /*
> * Do all necessary memory allocation before we lock the CIL.
> @@ -1081,10 +1079,6 @@ xfs_log_commit_cil(
>
> xlog_cil_insert_items(log, tp);
>
> - xc_commit_lsn = cil->xc_ctx->sequence;
> - if (commit_lsn)
> - *commit_lsn = xc_commit_lsn;
> -
> if (regrant && !XLOG_FORCED_SHUTDOWN(log))
> xfs_log_ticket_regrant(log, tp->t_ticket);
> else
> @@ -1107,8 +1101,10 @@ xfs_log_commit_cil(
> list_for_each_entry_safe(lip, next, &tp->t_items, li_trans) {
> xfs_trans_del_item(lip);
> if (lip->li_ops->iop_committing)
> - lip->li_ops->iop_committing(lip, xc_commit_lsn);
> + lip->li_ops->iop_committing(lip, cil->xc_ctx->sequence);
> }
> + if (commit_seq)
> + *commit_seq = cil->xc_ctx->sequence;
>
> /* xlog_cil_push_background() releases cil->xc_ctx_lock */
> xlog_cil_push_background(log);
> @@ -1125,9 +1121,9 @@ xfs_log_commit_cil(
> * iclog flush is necessary following this call.
> */
> xfs_lsn_t
> -xlog_cil_force_lsn(
> +xlog_cil_force_seq(
> struct xlog *log,
> - xfs_lsn_t sequence)
> + xfs_csn_t sequence)
> {
> struct xfs_cil *cil = log->l_cilp;
> struct xfs_cil_ctx *ctx;
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 0552e96d2b64..31ce2ce21e27 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -234,7 +234,7 @@ struct xfs_cil;
>
> struct xfs_cil_ctx {
> struct xfs_cil *cil;
> - xfs_lsn_t sequence; /* chkpt sequence # */
> + xfs_csn_t sequence; /* chkpt sequence # */
> xfs_lsn_t start_lsn; /* first LSN of chkpt commit */
> xfs_lsn_t commit_lsn; /* chkpt commit record lsn */
> struct xlog_ticket *ticket; /* chkpt ticket */
> @@ -272,10 +272,10 @@ struct xfs_cil {
> struct xfs_cil_ctx *xc_ctx;
>
> spinlock_t xc_push_lock ____cacheline_aligned_in_smp;
> - xfs_lsn_t xc_push_seq;
> + xfs_csn_t xc_push_seq;
> struct list_head xc_committing;
> wait_queue_head_t xc_commit_wait;
> - xfs_lsn_t xc_current_sequence;
> + xfs_csn_t xc_current_sequence;
> struct work_struct xc_push_work;
> wait_queue_head_t xc_push_wait; /* background push throttle */
> } ____cacheline_aligned_in_smp;
> @@ -552,19 +552,18 @@ int xlog_cil_init(struct xlog *log);
> void xlog_cil_init_post_recovery(struct xlog *log);
> void xlog_cil_destroy(struct xlog *log);
> bool xlog_cil_empty(struct xlog *log);
> +void xlog_cil_commit(struct xlog *log, struct xfs_trans *tp,
> + xfs_csn_t *commit_seq, bool regrant);
>
> /*
> * CIL force routines
> */
> -xfs_lsn_t
> -xlog_cil_force_lsn(
> - struct xlog *log,
> - xfs_lsn_t sequence);
> +xfs_lsn_t xlog_cil_force_seq(struct xlog *log, xfs_csn_t sequence);
>
> static inline void
> xlog_cil_force(struct xlog *log)
> {
> - xlog_cil_force_lsn(log, log->l_cilp->xc_current_sequence);
> + xlog_cil_force_seq(log, log->l_cilp->xc_current_sequence);
> }
>
> /*
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index b22a09e9daee..21ac7c048380 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -851,7 +851,7 @@ __xfs_trans_commit(
> bool regrant)
> {
> struct xfs_mount *mp = tp->t_mountp;
> - xfs_lsn_t commit_lsn = -1;
> + xfs_csn_t commit_seq = 0;
> int error = 0;
> int sync = tp->t_flags & XFS_TRANS_SYNC;
>
> @@ -893,7 +893,7 @@ __xfs_trans_commit(
> xfs_trans_apply_sb_deltas(tp);
> xfs_trans_apply_dquot_deltas(tp);
>
> - xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
> + xlog_cil_commit(mp->m_log, tp, &commit_seq, regrant);
>
> xfs_trans_free(tp);
>
> @@ -902,7 +902,7 @@ __xfs_trans_commit(
> * log out now and wait for it.
> */
> if (sync) {
> - error = xfs_log_force_lsn(mp, commit_lsn, XFS_LOG_SYNC, NULL);
> + error = xfs_log_force_seq(mp, commit_seq, XFS_LOG_SYNC, NULL);
> XFS_STATS_INC(mp, xs_trans_sync);
> } else {
> XFS_STATS_INC(mp, xs_trans_async);
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index 9dd745cf77c9..6276c7d251e6 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -43,7 +43,7 @@ struct xfs_log_item {
> struct list_head li_cil; /* CIL pointers */
> struct xfs_log_vec *li_lv; /* active log vector */
> struct xfs_log_vec *li_lv_shadow; /* standby vector */
> - xfs_lsn_t li_seq; /* CIL commit seq */
> + xfs_csn_t li_seq; /* CIL commit seq */
> };
>
> /*
> @@ -69,7 +69,7 @@ struct xfs_item_ops {
> void (*iop_pin)(struct xfs_log_item *);
> void (*iop_unpin)(struct xfs_log_item *, int remove);
> uint (*iop_push)(struct xfs_log_item *, struct list_head *);
> - void (*iop_committing)(struct xfs_log_item *, xfs_lsn_t commit_lsn);
> + void (*iop_committing)(struct xfs_log_item *lip, xfs_csn_t seq);
> void (*iop_release)(struct xfs_log_item *);
> xfs_lsn_t (*iop_committed)(struct xfs_log_item *, xfs_lsn_t);
> int (*iop_recover)(struct xfs_log_item *lip,
> --
> 2.28.0
>