On Mon, Sep 21, 2020 at 08:52:30PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > There's a subtle design flaw in the deferred log item code that can lead > to pinning the log tail. Taking up the defer ops chain examples from > the previous commit, we can get trapped in sequences like this: > > Caller hands us a transaction t0 with D0-D3 attached. The defer ops > chain will look like the following if the transaction rolls succeed: > > t1: D0(t0), D1(t0), D2(t0), D3(t0) > t2: d4(t1), d5(t1), D1(t0), D2(t0), D3(t0) > t3: d5(t1), D1(t0), D2(t0), D3(t0) > ... > t9: d9(t7), D3(t0) > t10: D3(t0) > t11: d10(t10), d11(t10) > t12: d11(t10) > > In transaction 9, we finish d9 and try to roll to t10 while holding onto > an intent item for D3 that we logged in t0. > > The previous commit changed the order in which we place new defer ops in > the defer ops processing chain to reduce the maximum chain length. Now > make xfs_defer_finish_noroll capable of relogging the entire chain > periodically so that we can always move the log tail forward. We do > this every seven loops, having observed that while most chains never > exceed seven items in length, the rest go far over that and seem to > be involved in most of the stall problems. > > Callers are now required to ensure that the transaction reservation is > large enough to handle logging done items and new intent items for the > maximum possible chain length. Most callers are careful to keep the > chain lengths low, so the overhead should be minimal. > > The decision to relog an intent item is made based on whether or not the > intent was added to the current checkpoint. If so, the checkpoint is > still open and there's no point in relogging. Otherwise, the old > checkpoint is closed and we relog the intent to add it to the current > one. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > --- > v2: combine /all/ the predicate functions into the relogging patch > --- Looks like there's still some unaccounted for feedback from the last variant that included the lsn logic: https://lore.kernel.org/linux-xfs/20200917152829.GC1874815@bfoster/ Brian > fs/xfs/libxfs/xfs_defer.c | 52 ++++++++++++++++++++++++++++++++++++++++++++ > fs/xfs/xfs_bmap_item.c | 27 +++++++++++++++++++++++ > fs/xfs/xfs_extfree_item.c | 29 +++++++++++++++++++++++++ > fs/xfs/xfs_log.c | 41 ++++++++++++++++++++++++++--------- > fs/xfs/xfs_log.h | 2 ++ > fs/xfs/xfs_refcount_item.c | 27 +++++++++++++++++++++++ > fs/xfs/xfs_rmap_item.c | 27 +++++++++++++++++++++++ > fs/xfs/xfs_trace.h | 1 + > fs/xfs/xfs_trans.h | 10 ++++++++ > 9 files changed, 206 insertions(+), 10 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c > index 84a70edd0da1..a6f57a918992 100644 > --- a/fs/xfs/libxfs/xfs_defer.c > +++ b/fs/xfs/libxfs/xfs_defer.c > @@ -17,6 +17,7 @@ > #include "xfs_inode_item.h" > #include "xfs_trace.h" > #include "xfs_icache.h" > +#include "xfs_log.h" > > /* > * Deferred Operations in XFS > @@ -361,6 +362,52 @@ xfs_defer_cancel_list( > } > } > > +/* > + * Prevent a log intent item from pinning the tail of the log by logging a > + * done item to release the intent item; and then log a new intent item. > + * The caller should provide a fresh transaction and roll it after we're done. > + */ > +static int > +xfs_defer_relog( > + struct xfs_trans **tpp, > + struct list_head *dfops) > +{ > + struct xfs_defer_pending *dfp; > + xfs_lsn_t threshold_lsn; > + > + ASSERT((*tpp)->t_flags & XFS_TRANS_PERM_LOG_RES); > + > + /* > + * Figure out where we need the tail to be in order to maintain the > + * minimum required free space in the log. > + */ > + threshold_lsn = xlog_grant_push_threshold((*tpp)->t_mountp->m_log, 0); > + if (threshold_lsn == NULLCOMMITLSN) > + return 0; > + > + list_for_each_entry(dfp, dfops, dfp_list) { > + /* > + * If the log intent item for this deferred op is behind the > + * desired log tail threshold and is not a part of the current > + * log checkpoint, relog the intent item to keep the log tail > + * moving forward. We're ok with this being racy because an > + * incorrect decision means we'll be a little slower at pushing > + * the tail. > + */ > + if (dfp->dfp_intent == NULL || > + XFS_LSN_CMP(dfp->dfp_intent->li_lsn, threshold_lsn) < 0 || > + xfs_log_item_in_current_chkpt(dfp->dfp_intent)) > + continue; > + > + trace_xfs_defer_relog_intent((*tpp)->t_mountp, dfp); > + dfp->dfp_intent = xfs_trans_item_relog(dfp->dfp_intent, *tpp); > + } > + > + if ((*tpp)->t_flags & XFS_TRANS_DIRTY) > + return xfs_defer_trans_roll(tpp); > + return 0; > +} > + > /* > * Log an intent-done item for the first pending intent, and finish the work > * items. > @@ -447,6 +494,11 @@ xfs_defer_finish_noroll( > if (error) > goto out_shutdown; > > + /* Every few rolls we relog all the intent items. */ > + error = xfs_defer_relog(tp, &dop_pending); > + if (error) > + goto out_shutdown; > + > dfp = list_first_entry(&dop_pending, struct xfs_defer_pending, > dfp_list); > error = xfs_defer_finish_one(*tp, dfp); > diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c > index 008436ef5bce..6317fdf4a3a0 100644 > --- a/fs/xfs/xfs_bmap_item.c > +++ b/fs/xfs/xfs_bmap_item.c > @@ -532,6 +532,32 @@ xfs_bui_item_match( > return BUI_ITEM(lip)->bui_format.bui_id == intent_id; > } > > +/* Relog an intent item to push the log tail forward. */ > +static struct xfs_log_item * > +xfs_bui_item_relog( > + struct xfs_log_item *intent, > + struct xfs_trans *tp) > +{ > + struct xfs_bud_log_item *budp; > + struct xfs_bui_log_item *buip; > + struct xfs_map_extent *extp; > + unsigned int count; > + > + count = BUI_ITEM(intent)->bui_format.bui_nextents; > + extp = BUI_ITEM(intent)->bui_format.bui_extents; > + > + tp->t_flags |= XFS_TRANS_DIRTY; > + budp = xfs_trans_get_bud(tp, BUI_ITEM(intent)); > + set_bit(XFS_LI_DIRTY, &budp->bud_item.li_flags); > + > + buip = xfs_bui_init(tp->t_mountp); > + memcpy(buip->bui_format.bui_extents, extp, count * sizeof(*extp)); > + atomic_set(&buip->bui_next_extent, count); > + xfs_trans_add_item(tp, &buip->bui_item); > + set_bit(XFS_LI_DIRTY, &buip->bui_item.li_flags); > + return &buip->bui_item; > +} > + > static const struct xfs_item_ops xfs_bui_item_ops = { > .iop_size = xfs_bui_item_size, > .iop_format = xfs_bui_item_format, > @@ -539,6 +565,7 @@ static const struct xfs_item_ops xfs_bui_item_ops = { > .iop_release = xfs_bui_item_release, > .iop_recover = xfs_bui_item_recover, > .iop_match = xfs_bui_item_match, > + .iop_relog = xfs_bui_item_relog, > }; > > /* > diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c > index 337fae015bca..30a53f3913d1 100644 > --- a/fs/xfs/xfs_extfree_item.c > +++ b/fs/xfs/xfs_extfree_item.c > @@ -642,6 +642,34 @@ xfs_efi_item_match( > return EFI_ITEM(lip)->efi_format.efi_id == intent_id; > } > > +/* Relog an intent item to push the log tail forward. */ > +static struct xfs_log_item * > +xfs_efi_item_relog( > + struct xfs_log_item *intent, > + struct xfs_trans *tp) > +{ > + struct xfs_efd_log_item *efdp; > + struct xfs_efi_log_item *efip; > + struct xfs_extent *extp; > + unsigned int count; > + > + count = EFI_ITEM(intent)->efi_format.efi_nextents; > + extp = EFI_ITEM(intent)->efi_format.efi_extents; > + > + tp->t_flags |= XFS_TRANS_DIRTY; > + efdp = xfs_trans_get_efd(tp, EFI_ITEM(intent), count); > + efdp->efd_next_extent = count; > + memcpy(efdp->efd_format.efd_extents, extp, count * sizeof(*extp)); > + set_bit(XFS_LI_DIRTY, &efdp->efd_item.li_flags); > + > + efip = xfs_efi_init(tp->t_mountp, count); > + memcpy(efip->efi_format.efi_extents, extp, count * sizeof(*extp)); > + atomic_set(&efip->efi_next_extent, count); > + xfs_trans_add_item(tp, &efip->efi_item); > + set_bit(XFS_LI_DIRTY, &efip->efi_item.li_flags); > + return &efip->efi_item; > +} > + > static const struct xfs_item_ops xfs_efi_item_ops = { > .iop_size = xfs_efi_item_size, > .iop_format = xfs_efi_item_format, > @@ -649,6 +677,7 @@ static const struct xfs_item_ops xfs_efi_item_ops = { > .iop_release = xfs_efi_item_release, > .iop_recover = xfs_efi_item_recover, > .iop_match = xfs_efi_item_match, > + .iop_relog = xfs_efi_item_relog, > }; > > /* > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > index ad0c69ee8947..62c9e0aaa7df 100644 > --- a/fs/xfs/xfs_log.c > +++ b/fs/xfs/xfs_log.c > @@ -1475,14 +1475,15 @@ xlog_commit_record( > } > > /* > - * Push on the buffer cache code if we ever use more than 75% of the on-disk > - * log space. This code pushes on the lsn which would supposedly free up > - * the 25% which we want to leave free. We may need to adopt a policy which > - * pushes on an lsn which is further along in the log once we reach the high > - * water mark. In this manner, we would be creating a low water mark. > + * Compute the LSN push target needed to push on the buffer cache code if we > + * ever use more than 75% of the on-disk log space. This code pushes on the > + * lsn which would supposedly free up the 25% which we want to leave free. We > + * may need to adopt a policy which pushes on an lsn which is further along in > + * the log once we reach the high water mark. In this manner, we would be > + * creating a low water mark. > */ > -STATIC void > -xlog_grant_push_ail( > +xfs_lsn_t > +xlog_grant_push_threshold( > struct xlog *log, > int need_bytes) > { > @@ -1508,7 +1509,7 @@ xlog_grant_push_ail( > free_threshold = max(free_threshold, (log->l_logBBsize >> 2)); > free_threshold = max(free_threshold, 256); > if (free_blocks >= free_threshold) > - return; > + return NULLCOMMITLSN; > > xlog_crack_atomic_lsn(&log->l_tail_lsn, &threshold_cycle, > &threshold_block); > @@ -1528,13 +1529,33 @@ xlog_grant_push_ail( > if (XFS_LSN_CMP(threshold_lsn, last_sync_lsn) > 0) > threshold_lsn = last_sync_lsn; > > + return threshold_lsn; > +} > + > +/* > + * Push on the buffer cache code if we ever use more than 75% of the on-disk > + * log space. This code pushes on the lsn which would supposedly free up > + * the 25% which we want to leave free. We may need to adopt a policy which > + * pushes on an lsn which is further along in the log once we reach the high > + * water mark. In this manner, we would be creating a low water mark. > + */ > +STATIC void > +xlog_grant_push_ail( > + struct xlog *log, > + int need_bytes) > +{ > + xfs_lsn_t threshold_lsn; > + > + threshold_lsn = xlog_grant_push_threshold(log, need_bytes); > + if (threshold_lsn == NULLCOMMITLSN || XLOG_FORCED_SHUTDOWN(log)) > + return; > + > /* > * Get the transaction layer to kick the dirty buffers out to > * disk asynchronously. No point in trying to do this if > * the filesystem is shutting down. > */ > - if (!XLOG_FORCED_SHUTDOWN(log)) > - xfs_ail_push(log->l_ailp, threshold_lsn); > + xfs_ail_push(log->l_ailp, threshold_lsn); > } > > /* > diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h > index 1412d6993f1e..58c3fcbec94a 100644 > --- a/fs/xfs/xfs_log.h > +++ b/fs/xfs/xfs_log.h > @@ -141,4 +141,6 @@ void xfs_log_quiesce(struct xfs_mount *mp); > bool xfs_log_check_lsn(struct xfs_mount *, xfs_lsn_t); > bool xfs_log_in_recovery(struct xfs_mount *); > > +xfs_lsn_t xlog_grant_push_threshold(struct xlog *log, int need_bytes); > + > #endif /* __XFS_LOG_H__ */ > diff --git a/fs/xfs/xfs_refcount_item.c b/fs/xfs/xfs_refcount_item.c > index c78412755b8a..cf0205fdc607 100644 > --- a/fs/xfs/xfs_refcount_item.c > +++ b/fs/xfs/xfs_refcount_item.c > @@ -560,6 +560,32 @@ xfs_cui_item_match( > return CUI_ITEM(lip)->cui_format.cui_id == intent_id; > } > > +/* Relog an intent item to push the log tail forward. */ > +static struct xfs_log_item * > +xfs_cui_item_relog( > + struct xfs_log_item *intent, > + struct xfs_trans *tp) > +{ > + struct xfs_cud_log_item *cudp; > + struct xfs_cui_log_item *cuip; > + struct xfs_phys_extent *extp; > + unsigned int count; > + > + count = CUI_ITEM(intent)->cui_format.cui_nextents; > + extp = CUI_ITEM(intent)->cui_format.cui_extents; > + > + tp->t_flags |= XFS_TRANS_DIRTY; > + cudp = xfs_trans_get_cud(tp, CUI_ITEM(intent)); > + set_bit(XFS_LI_DIRTY, &cudp->cud_item.li_flags); > + > + cuip = xfs_cui_init(tp->t_mountp, count); > + memcpy(cuip->cui_format.cui_extents, extp, count * sizeof(*extp)); > + atomic_set(&cuip->cui_next_extent, count); > + xfs_trans_add_item(tp, &cuip->cui_item); > + set_bit(XFS_LI_DIRTY, &cuip->cui_item.li_flags); > + return &cuip->cui_item; > +} > + > static const struct xfs_item_ops xfs_cui_item_ops = { > .iop_size = xfs_cui_item_size, > .iop_format = xfs_cui_item_format, > @@ -567,6 +593,7 @@ static const struct xfs_item_ops xfs_cui_item_ops = { > .iop_release = xfs_cui_item_release, > .iop_recover = xfs_cui_item_recover, > .iop_match = xfs_cui_item_match, > + .iop_relog = xfs_cui_item_relog, > }; > > /* > diff --git a/fs/xfs/xfs_rmap_item.c b/fs/xfs/xfs_rmap_item.c > index c1a1fd62ca74..3237243d375d 100644 > --- a/fs/xfs/xfs_rmap_item.c > +++ b/fs/xfs/xfs_rmap_item.c > @@ -583,6 +583,32 @@ xfs_rui_item_match( > return RUI_ITEM(lip)->rui_format.rui_id == intent_id; > } > > +/* Relog an intent item to push the log tail forward. */ > +static struct xfs_log_item * > +xfs_rui_item_relog( > + struct xfs_log_item *intent, > + struct xfs_trans *tp) > +{ > + struct xfs_rud_log_item *rudp; > + struct xfs_rui_log_item *ruip; > + struct xfs_map_extent *extp; > + unsigned int count; > + > + count = RUI_ITEM(intent)->rui_format.rui_nextents; > + extp = RUI_ITEM(intent)->rui_format.rui_extents; > + > + tp->t_flags |= XFS_TRANS_DIRTY; > + rudp = xfs_trans_get_rud(tp, RUI_ITEM(intent)); > + set_bit(XFS_LI_DIRTY, &rudp->rud_item.li_flags); > + > + ruip = xfs_rui_init(tp->t_mountp, count); > + memcpy(ruip->rui_format.rui_extents, extp, count * sizeof(*extp)); > + atomic_set(&ruip->rui_next_extent, count); > + xfs_trans_add_item(tp, &ruip->rui_item); > + set_bit(XFS_LI_DIRTY, &ruip->rui_item.li_flags); > + return &ruip->rui_item; > +} > + > static const struct xfs_item_ops xfs_rui_item_ops = { > .iop_size = xfs_rui_item_size, > .iop_format = xfs_rui_item_format, > @@ -590,6 +616,7 @@ static const struct xfs_item_ops xfs_rui_item_ops = { > .iop_release = xfs_rui_item_release, > .iop_recover = xfs_rui_item_recover, > .iop_match = xfs_rui_item_match, > + .iop_relog = xfs_rui_item_relog, > }; > > /* > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h > index a3a35a2d8ed9..362c155be525 100644 > --- a/fs/xfs/xfs_trace.h > +++ b/fs/xfs/xfs_trace.h > @@ -2533,6 +2533,7 @@ DEFINE_DEFER_PENDING_EVENT(xfs_defer_create_intent); > DEFINE_DEFER_PENDING_EVENT(xfs_defer_cancel_list); > DEFINE_DEFER_PENDING_EVENT(xfs_defer_pending_finish); > DEFINE_DEFER_PENDING_EVENT(xfs_defer_pending_abort); > +DEFINE_DEFER_PENDING_EVENT(xfs_defer_relog_intent); > > #define DEFINE_BMAP_FREE_DEFERRED_EVENT DEFINE_PHYS_EXTENT_DEFERRED_EVENT > DEFINE_BMAP_FREE_DEFERRED_EVENT(xfs_bmap_free_defer); > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h > index 995c1513693c..e838e8327510 100644 > --- a/fs/xfs/xfs_trans.h > +++ b/fs/xfs/xfs_trans.h > @@ -78,6 +78,8 @@ struct xfs_item_ops { > int (*iop_recover)(struct xfs_log_item *lip, > struct xfs_defer_capture **dfcp); > bool (*iop_match)(struct xfs_log_item *item, uint64_t id); > + struct xfs_log_item *(*iop_relog)(struct xfs_log_item *intent, > + struct xfs_trans *tp); > }; > > /* > @@ -239,4 +241,12 @@ void xfs_trans_buf_copy_type(struct xfs_buf *dst_bp, > > extern kmem_zone_t *xfs_trans_zone; > > +static inline struct xfs_log_item * > +xfs_trans_item_relog( > + struct xfs_log_item *lip, > + struct xfs_trans *tp) > +{ > + return lip->li_ops->iop_relog(lip, tp); > +} > + > #endif /* __XFS_TRANS_H__ */ >
