linux-kernel - XFS mount timeout in linux-6.9.11

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Message-ID: <71864473-f0f7-41c3-95f2-c78f6edcfab9@gmail.com>
Date: Fri, 9 Aug 2024 19:08:41 +0200
From: Anders Blomdell <anders.blomdell@...il.com>
To: linux-xfs@...r.kernel.org,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Chandan Babu R <chandan.babu@...cle.com>,
 "Darrick J. Wong" <djwong@...nel.org>, Christoph Hellwig <hch@....de>
Subject: XFS mount timeout in linux-6.9.11

With a filesystem that contains a very large amount of hardlinks
the time to mount the filesystem skyrockets to around 15 minutes
on 6.9.11-200.fc40.x86_64 as compared to around 1 second on
6.8.10-300.fc40.x86_64, this of course makes booting drop
into emergency mode if the filesystem is in /etc/fstab. A git bisect
nails the offending commit as 14dd46cf31f4aaffcf26b00de9af39d01ec8d547.

The filesystem is a collection of daily snapshots of a live filesystem
collected over a number of years, organized as a storage of unique files,
that are reflinked to inodes that contain the actual {owner,group,permission,
mtime}, and these inodes are hardlinked into the daily snapshot trees.

The numbers for the filesystem are:

   Total file size:           3.6e+12 bytes
   Unique files:             12.4e+06
   Reflink inodes:           18.6e+06
   Hardlinks:                15.7e+09

Timing between the systems are:

   6.8.10-300.fc40.x86_64:

     # time mount /dev/vg1/test /test
     real	0m0.835s
     user	0m0.002s
     sys	        0m0.014s

   6.9.11-200.fc40.x86_64:

     # time mount /dev/vg1/test /test
     real	15m36.508s
     user	0m0.000s
     sys	        0m27.628s

     (iotop reports 1-4 MB/s)