From: Daejun Park <[email protected]>

A whole-device FITRIM walks every AG but the last by length, in
batches. xfs_trim_gather_extents() saves the record to restart from in
tcur->start. But tcur->start is also the start of the range to trim.
Later batches therefore never discard the free extents below that
block.

Save the restart record in a new restart_bno field.

Cc: [email protected] # v6.10
Fixes: b0ffe661fab4 ("xfs: fix performance problems when fstrimming a subset of 
a fragmented AG")
Signed-off-by: Daejun Park <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
(cherry picked from commit 595e67d7261673d03c96950ffbb2e545c00376ed)

https://virtuozzo.atlassian.net/browse/VSTOR-153590

Feature: fix ms/xfs
Signed-off-by: Denis V. Lunev <[email protected]>
---

Notes:
    A clean cherry-pick of mainline 595e67d72616 (v7.4-rc2), no changes.
    hci-8.1 has the RHEL backport of b0ffe661fab4 it fixes.

 fs/xfs/xfs_discard.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
index 93943e698eea..41c98f9abde1 100644
--- a/fs/xfs/xfs_discard.c
+++ b/fs/xfs/xfs_discard.c
@@ -181,6 +181,8 @@ struct xfs_trim_cur {
        xfs_agblock_t   end;
        xfs_extlen_t    minlen;
        bool            by_bno;
+       /* restart point (with count) for the by-length walk */
+       xfs_agblock_t   restart_bno;
 };
 
 static int
@@ -226,14 +228,15 @@ xfs_trim_gather_extents(
                error = xfs_alloc_lookup_le(cur, tcur->start, 0, &i);
                if (!error && !i)
                        error = xfs_alloc_lookup_ge(cur, tcur->start, 0, &i);
-       } else if (tcur->start == 0) {
+       } else if (tcur->restart_bno == NULLAGBLOCK) {
                /* first time through a by-len starts with max length */
                cur = xfs_cntbt_init_cursor(mp, tp, agbp, pag);
                error = xfs_alloc_lookup_ge(cur, 0, tcur->count, &i);
        } else {
                /* nth time through a by-len starts where we left off */
                cur = xfs_cntbt_init_cursor(mp, tp, agbp, pag);
-               error = xfs_alloc_lookup_le(cur, tcur->start, tcur->count, &i);
+               error = xfs_alloc_lookup_le(cur, tcur->restart_bno,
+                                           tcur->count, &i);
        }
        if (error)
                goto out_del_cursor;
@@ -263,9 +266,15 @@ xfs_trim_gather_extents(
                if (--batch <= 0) {
                        /*
                         * Update the cursor to point at this extent so we
-                        * restart the next batch from this extent.
+                        * restart the next batch from this extent. The
+                        * by-length walk does not visit extents in block
+                        * order, so it must keep the start of the range and
+                        * restart from restart_bno instead.
                         */
-                       tcur->start = fbno;
+                       if (tcur->by_bno)
+                               tcur->start = fbno;
+                       else
+                               tcur->restart_bno = fbno;
                        tcur->count = flen;
                        break;
                }
@@ -368,6 +377,7 @@ xfs_trim_perag_extents(
                .start          = start,
                .end            = end,
                .minlen         = minlen,
+               .restart_bno    = NULLAGBLOCK,
        };
        int                     error = 0;
 
-- 
2.53.0

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