[LU-9977] client ran out of memory when diffing two 2GB files

• Type: Bug
• Resolution: Not a Bug
• Priority: Critical
• Affects Version/s: Lustre 2.11.0, Lustre 2.10.2
• Environment: clients: trevis-60vm1 & 2; mds: trevis-62; ost: trevis-65; ; before upgrade: el7.3, zfs 6.5.9, b2_10 branch, v2.10.0, b5 ; after upgrade: el7.4, zfs 7.1, master branch, v2.10.52, b3631
• Severity: 3
• Assignee: Zhenyu Xu
• Reporter: James Casper

Description

Systems were imaged to el7.3/lustre2.10.0. A zfs mount point (v6.5.9) was
created on the lustre file system. A 2GB file was then copied to a directory on
the zfs mount point.

After systems were imaged to el7.4/2.10.52, an import of the 6.5.9 zpool was
performed. A 2GB file was then copied onto the zfs mount point (same file as
above - different directory). Diff was then used to compare the two files.

While diff was running, top showed it consuming 80-90% of memory. At some
point close to 90%, the client killed the diff process.

I've found two ways to avoid this:

1) Keep everything above the same except work with a newly created zfs pool
rather than an imported pool.

2) Instead of diffing two 2GB files, diff two 2GB sets of several smaller
files (largest file in set <60MB).

Note: When diff is used to compare several smaller files, it uses much less
memory (<10%).

Note: This has also been seen with ldiskfs, but is easier to repro with zfs.

Issue Links

• is related to: LU-9601 recovery-mds-scale test_failover_mds: test_failover_mds returned 1