Linux 6.18 Will Fix Lockups When Systemd Units Read Lots of Files

7 months ago

Linux 6.18 will fix lockups caused by systemd units reading many files with the 'lazytime' mount option.
The issue occurs when dirty inodes accumulate to 'hundreds of thousands or millions' during cgroup exit, causing hours of 100% CPU usage.
Microsoft engineer Christian Brauner submitted 12 pull requests, including one addressing this writeback code problem.
The 'lazytime' option delays on-disk timestamp updates for performance, but triggers excessive inode switching during cgroup exits.
The fix involves optimizing the inode switching logic, which currently has quadratic time complexity.
A sample script is provided to reproduce the issue on current Linux kernels.
The solution will be included in the Linux 6.18 merge window.

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