[LU-12337] SoM in DoM needs to work transparently

• Status: Resolved
• Project: Lustre
• Affects Version/s: Lustre 2.13.0
• Type: Bug
• Priority: Minor
• Reporter: Shuichi Ihara
• Assignee: WC Triage
• Resolution: Fixed

Environment

master

• Severity: 3

Description

If all data are in DoM (no other components in OSTs), file size should be already stored into MDT object because of DoM.
It doesn't need SoM with DoM, but 'lfs getsom' needs to work transparently same as non-DoM files.
Here is an issue of 'lfs getsom' with DoM.

[root@c01 ~]# mkdir /cache1/dom
[root@c01 ~]# lfs setstripe -L mdt -E 2M /cache1/dom
[root@c01 ~]# pdsh -w c[01-02] lctl set_param ldlm.namespaces.*.lru_size=clear
[root@c01 ~]# pdsh -w es400nv-vm[1-4] "echo 3 > /proc/sys/vm/drop_caches"
[root@c01 ~]# lctl get_param ldlm.namespaces.*MDT0000*.lock_count
ldlm.namespaces.cache1-MDT0000-mdc-ffff97f3bc25d000.lock_count=0

Create an file on c01
[root@c01 ~]# dd if=/dev/zero of=/cache1/dom/file bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.00162115 s, 647 MB/s

Run 'lfs getsom' on c02 (different client)
[root@c02 ~]# lfs getsom -s /cache1/nondom/file
/cache1/nondom/file failed to get som xattr: No such file or directory (2)

Also, even 'lfs getsom' works with DoM, we don't want lock cancellation for OST objects after fetch SOM.
Please see below SoM for non-DoM configuration.

[root@c01 ~]# mkdir /cache1/nondom
[root@c01 ~]# lfs setstripe -i 0 /cache1/nondom/
[root@c01 ~]# pdsh -w c[01-02] lctl set_param ldlm.namespaces.*.lru_size=clear
[root@c01 ~]# pdsh -w es400nv-vm[1-4] "echo 3 > /proc/sys/vm/drop_caches"

[root@c01 ~]# lctl get_param ldlm.namespaces.*0000*.lock_count
ldlm.namespaces.cache1-MDT0000-mdc-ffff97f3bc25d000.lock_count=0
ldlm.namespaces.cache1-OST0000-osc-ffff97f3bc25d000.lock_count=0

Create an file on c01
[root@c01 ~]# dd if=/dev/zero of=/cache1/nondom/file bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.00185952 s, 564 MB/s
[root@c01 ~]#  lctl get_param ldlm.namespaces.*0000*.lock_count
ldlm.namespaces.cache1-MDT0000-mdc-ffff97f3bc25d000.lock_count=3
ldlm.namespaces.cache1-OST0000-osc-ffff97f3bc25d000.lock_count=1

Even run 'lfs getsom' on c02, no lock cancellation on c01
[root@c02 ~]# lfs getsom -s /cache1/nondom/file
[root@c01 ~]# lctl get_param ldlm.namespaces.*0000*.lock_count
ldlm.namespaces.cache1-MDT0000-mdc-ffff97f3bc25d000.lock_count=3
ldlm.namespaces.cache1-OST0000-osc-ffff97f3bc25d000.lock_count=1

Issue Links

• is related to: LU-11962 File LSOM updates to store proper siz...
• is related to: LU-11367 integrate LSOM with lfs find

Comments

[Andreas Dilger]

For lfs getsom I don't really want this to be the primary interface for accessing SOM data, but I agree it makes sense to be consistent. For DoM file's it should be possible to generate a fake trusted.som xattr on the client based on the in-memory size.

[Andreas Dilger]

Shuichi, IMHO "lfs getsom" shouldn't be more than a debugging tool for testing. We now have proper LSOM access via statx(), and "lfs find -lazy", and if LU-11962 is implemented we could have proper SOM for normal "stat()" calls for files that are not being modified.

I'd rather spend effort on LU-11962 than making "lfs getsom" work for DoM files. What do you think?

[Andreas Dilger]

Mike, I think that this is now the case, that if the DoM component is the only initialized component of the file, then the MDS returns the size to the client for stat()?

[Mikhail Pershin]

Andreas, yes, MDS returns DoM size to a client

[Andreas Dilger]

I think this was fixed as part of the statx() patches.