xfs: periodically relog deferred intent itemsdefer-ops-stalls_2020-10-10

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 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@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

7 files changed, 173 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index 8d42b914dcd4..5e5806d0b161 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
@@ -346,6 +347,52 @@ 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.
  */
@@ -431,6 +478,11 @@ xfs_defer_finish_noroll(
 		if (error)
 			goto out_shutdown;
 
+		/* Possibly relog intent items to keep the log moving. */
+		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 fa52bfd66ce1..27b0d3fb7654 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 be0186875566..031bcd935072 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 7a57b4de9ee7..d1ad73eb8d46 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 16c7a6385c3f..014472f5f436 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 e27df685d3cd..aad31c3a6975 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -77,6 +77,8 @@ struct xfs_item_ops {
 	int (*iop_recover)(struct xfs_log_item *lip,
 			   struct list_head *capture_list);
 	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);
 };
 
 /*
@@ -238,4 +240,12 @@ 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__ */