lkml.org 
[lkml]   [2019]   [Dec]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.19 43/47] dm btree: increase rebalance threshold in __rebalance2()
Date
From: Hou Tao <houtao1@huawei.com>

commit 474e559567fa631dea8fb8407ab1b6090c903755 upstream.

We got the following warnings from thin_check during thin-pool setup:

$ thin_check /dev/vdb
examining superblock
examining devices tree
missing devices: [1, 84]
too few entries in btree_node: 41, expected at least 42 (block 138, max_entries = 126)
examining mapping tree

The phenomenon is the number of entries in one node of details_info tree is
less than (max_entries / 3). And it can be easily reproduced by the following
procedures:

$ new a thin pool
$ presume the max entries of details_info tree is 126
$ new 127 thin devices (e.g. 1~127) to make the root node being full
and then split
$ remove the first 43 (e.g. 1~43) thin devices to make the children
reblance repeatedly
$ stop the thin pool
$ thin_check

The root cause is that the B-tree removal procedure in __rebalance2()
doesn't guarantee the invariance: the minimal number of entries in
non-root node should be >= (max_entries / 3).

Simply fix the problem by increasing the rebalance threshold to
make sure the number of entries in each child will be greater
than or equal to (max_entries / 3 + 1), so no matter which
child is used for removal, the number will still be valid.

Cc: stable@vger.kernel.org
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/persistent-data/dm-btree-remove.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/md/persistent-data/dm-btree-remove.c
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -203,7 +203,13 @@ static void __rebalance2(struct dm_btree
struct btree_node *right = r->n;
uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
- unsigned threshold = 2 * merge_threshold(left) + 1;
+ /*
+ * Ensure the number of entries in each child will be greater
+ * than or equal to (max_entries / 3 + 1), so no matter which
+ * child is used for removal, the number will still be not
+ * less than (max_entries / 3).
+ */
+ unsigned int threshold = 2 * (merge_threshold(left) + 1);

if (nr_left + nr_right < threshold) {
/*

\
 
 \ /
  Last update: 2019-12-19 20:00    [W:0.138 / U:0.552 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site