xfs: compute data device CoW staging extent reap limits dynamically

Calculate the maximum number of CoW staging extents that can be reaped
in a single transaction chain.  The rough calculation here is:

nr_extents = (logres - reservation used by any one step) /
		(space used by intents per extent +
		 space used for a few buffer invalidations)

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/scrub/reap.c b/fs/xfs/scrub/reap.c
index 929ea3c453d313d1ab659c45857eab6add67491c..aaef7e6771a04513f337084745617892658ed99e 100644 (file)
--- a/fs/xfs/scrub/reap.c
+++ b/fs/xfs/scrub/reap.c
@@ -443,7 +443,7 @@ xreap_agextent_iter(
 
                if (rs->oinfo == &XFS_RMAP_OINFO_COW) {
                        /*
-                        * If we're unmapping CoW staging extents, remove the
+                        * t0: Unmapping CoW staging extents, remove the
                         * records from the refcountbt, which will remove the
                         * rmap record as well.
                         */
@@ -475,7 +475,7 @@ xreap_agextent_iter(
        }
 
        /*
-        * If we're getting rid of CoW staging extents, use deferred work items
+        * t2: To get rid of CoW staging extents, use deferred work items
         * to remove the refcountbt records (which removes the rmap records)
         * and free the extent.  We're not worried about the system going down
         * here because log recovery walks the refcount btree to clean out the
@@ -626,6 +626,84 @@ xreap_configure_agextent_limits(
                        step_size, per_intent, rs->max_deferred);
 }
 
+/*
+ * Compute the maximum number of intent items that reaping can attach to the
+ * scrub transaction given the worst case log overhead of the intent items
+ * needed to reap a single CoW staging extent.  This is not for freeing
+ * metadata blocks.
+ */
+STATIC void
+xreap_configure_agcow_limits(
+       struct xreap_state      *rs)
+{
+       struct xfs_scrub        *sc = rs->sc;
+       struct xfs_mount        *mp = sc->mp;
+
+       /*
+        * In the worst case, relogging an intent item causes both an intent
+        * item and a done item to be attached to a transaction for each extent
+        * that we'd like to process.
+        */
+       const unsigned int      efi = xfs_efi_log_space(1) +
+                                     xfs_efd_log_space(1);
+       const unsigned int      rui = xfs_rui_log_space(1) +
+                                     xfs_rud_log_space();
+       const unsigned int      cui = xfs_cui_log_space(1) +
+                                     xfs_cud_log_space();
+
+       /*
+        * Various things can happen when reaping non-CoW metadata blocks:
+        *
+        * t0: Unmapping crosslinked CoW blocks: deferred removal of refcount
+        * record, which defers removal of rmap record
+        *
+        * t2: Freeing CoW blocks: deferred removal of refcount record, which
+        * defers removal of rmap record; and deferred removal of the space
+        *
+        * For simplicity, we'll use the worst-case intents size to determine
+        * the maximum number of deferred extents before we have to finish the
+        * whole chain.  If we're trying to reap a btree larger than this size,
+        * a crash midway through reaping can result in leaked blocks.
+        */
+       const unsigned int      t0 = cui + rui;
+       const unsigned int      t2 = cui + rui + efi;
+       const unsigned int      per_intent = max(t0, t2);
+
+       /*
+        * For each transaction in a reap chain, we must be able to take one
+        * step in the defer item chain, which should only consist of CUI, EFI,
+        * or RUI items.
+        */
+       const unsigned int      f1 = xfs_calc_finish_efi_reservation(mp, 1);
+       const unsigned int      f2 = xfs_calc_finish_rui_reservation(mp, 1);
+       const unsigned int      f3 = xfs_calc_finish_cui_reservation(mp, 1);
+       const unsigned int      step_size = max3(f1, f2, f3);
+
+       /* Largest buffer size (in fsblocks) that can be invalidated. */
+       const unsigned int      max_binval = xrep_binval_max_fsblocks(mp);
+
+       /* Overhead of invalidating one buffer */
+       const unsigned int      per_binval =
+               xfs_buf_inval_log_space(1, XFS_B_TO_FSBT(mp, max_binval));
+
+       /*
+        * For each transaction in a reap chain, we can delete some number of
+        * extents and invalidate some number of blocks.  We assume that CoW
+        * staging extents are usually more than 1 fsblock, and that there
+        * shouldn't be any buffers for those blocks.  From the assumptions,
+        * set the number of deferrals to use as much of the reservation as
+        * it can, but leave space to invalidate 1/8th that number of buffers.
+        */
+       const unsigned int      variable_overhead = per_intent +
+                                                       (per_binval / 8);
+
+       xreap_configure_limits(rs, step_size, variable_overhead, per_intent,
+                       per_binval);
+
+       trace_xreap_agcow_limits(sc->tp, per_binval, rs->max_binval, step_size,
+                       per_intent, rs->max_deferred);
+}
+
 /*
  * Break an AG metadata extent into sub-extents by fate (crosslinked, not
  * crosslinked), and dispose of each sub-extent separately.
@@ -800,15 +878,15 @@ xrep_reap_fsblocks(
                .sc                     = sc,
                .oinfo                  = oinfo,
                .resv                   = XFS_AG_RESV_NONE,
-               .max_binval             = XREAP_MAX_BINVAL,
-               .max_deferred           = XREAP_MAX_DEFER_CHAIN,
        };
        int                             error;
 
        ASSERT(xfs_has_rmapbt(sc->mp));
        ASSERT(sc->ip != NULL);
 
-       if (oinfo != &XFS_RMAP_OINFO_COW)
+       if (oinfo == &XFS_RMAP_OINFO_COW)
+               xreap_configure_agcow_limits(&rs);
+       else
                xreap_configure_agextent_limits(&rs);
        error = xfsb_bitmap_walk(bitmap, xreap_fsmeta_extent, &rs);
        if (error)

diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index d39da0e67024fbefbcddb3c5f49b6334ac565cba..a9da22f50534cb9038e0cff4e3ff4a3e6d302dae 100644 (file)
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -2041,6 +2041,7 @@ DEFINE_EVENT(xrep_reap_limits_class, name, \
                 unsigned int max_deferred), \
        TP_ARGS(tp, per_binval, max_binval, step_size, per_intent, max_deferred))
 DEFINE_REPAIR_REAP_LIMITS_EVENT(xreap_agextent_limits);
+DEFINE_REPAIR_REAP_LIMITS_EVENT(xreap_agcow_limits);
 
 DECLARE_EVENT_CLASS(xrep_reap_find_class,
        TP_PROTO(const struct xfs_group *xg, xfs_agblock_t agbno,