On Fri, Sep 25, 2020 at 07:15:40AM -0400, Brian Foster wrote: > On Tue, Sep 22, 2020 at 10:33:19PM -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. Most > > chains will never get relogged, except for operations that generate very > > long chains (large extents containing many blocks with different sharing > > levels) or are on filesystems with small logs and a lot of ongoing > > metadata updates. > > > > 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. > > > > Looks like this last bit needs to be updated. Yep. The next version will replace that paragraph with the following: "The decision to relog an intent item is made based on two factors: (a) whether the intent was logged in a previous checkpoint, and (b) if the log has hit the 75% full threshold. There's no point in relogging an intent into the same checkpoint, and there's no need to relog if there's plenty of free space in the log." > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > --- > > fs/xfs/libxfs/xfs_defer.c | 52 ++++++++++++++++++++++++++++++++++++++++++++ > > fs/xfs/xfs_bmap_item.c | 27 +++++++++++++++++++++++ > > fs/xfs/xfs_extfree_item.c | 29 +++++++++++++++++++++++++ > > 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 ++++++++ > > 7 files changed, 173 insertions(+) > > > > > > diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c > > index 84a70edd0da1..c601cc2af254 100644 > > --- a/fs/xfs/libxfs/xfs_defer.c > > +++ b/fs/xfs/libxfs/xfs_defer.c > ... > > @@ -447,6 +494,11 @@ xfs_defer_finish_noroll( > > if (error) > > goto out_shutdown; > > > > + /* Every few rolls we relog all the intent items. */ > > Stale comment? Yes. Change that to: /* Possibly relog intent items to keep the log tail moving. */ > Those nits aside: > > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> Thanks for the review! --D > > + 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_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__ */ > > >