[LU-6371] sendfile with group lock splits transfer into tiny chunks

• Type: Bug
• Resolution: Duplicate
• Priority: Major
• Affects Version/s: Lustre 2.7.0
• Severity: 3
• Assignee: WC Triage
• Reporter: Frank Zago (Inactive)

Description

A program using sendfile to copy a file from lustre to lustre, with a group lock on its source will see the transfer split in tiny chunks.

Reproducer attached.

Test setup. Create a 100MiB file.

$ pwd
/mnt/lustre
$ dd if=/dev/zero of=foo1 bs=1M count=100 

Transfer without a group lock:

$ strace ~/lustre-cleanup/lustre/tests/llsendfile4 0 foo1 foo2
...
sendfile(4, 3, NULL, 10485760)          = 10485760
sendfile(4, 3, NULL, 10485760)          = 10485760
sendfile(4, 3, NULL, 10485760)          = 10485760
sendfile(4, 3, NULL, 10485760)          = 10485760
sendfile(4, 3, NULL, 10485760)          = 10485760
sendfile(4, 3, NULL, 10485760)          = 10485760
...

With a group lock

$ strace ~/lustre-cleanup/lustre/tests/llsendfile4 1223 foo1 foo2
...
sendfile(4, 3, NULL, 10485760)          = 28672
sendfile(4, 3, NULL, 10485760)          = 4096
sendfile(4, 3, NULL, 10485760)          = 4096
sendfile(4, 3, NULL, 10485760)          = 8192
sendfile(4, 3, NULL, 10485760)          = 4096
sendfile(4, 3, NULL, 10485760)          = 4096
sendfile(4, 3, NULL, 10485760)          = 4096
...

The second example takes about 10 times longer than the first.

Issue Links

• is related to: LU-6368 ASSERTION( cur->oe_dlmlock == victim->oe_dlmlock ) failed