Hi. While this bug was fixed for 5.4/5.15, it still exists in 5.19 and
later kernel releases.
The SAUCE patch that resolved this ("Make NFS file-access stale cache behavior
opt-in", which added the nfs_fasc module parameter, does not appear to have
been forward-ported.
Checked /sys/module/nfs/parameters/ with the nfs module loaded on 5.19, 6.8 and
7.0 -- nfs_fasc is absent on all three. fs/nfs/dir.c in the linux-aws-5.19
source
(5.19.0-1029.30~22.04.1) contains no reference to it, and the per-login access
cache invalidation is unconditional there.
So the original symptom is back for anyone on a newer kernel. Measured with
OpenSSH sshd reading AuthorizedKeysFile from an NFSv4.1 home directory, 20
sequential SFTP logins, all hosts c6i.xlarge in a single AZ with CPU steal at
zero:
Ubuntu kernel ACCESS RPCs/login login median @1
22.04 5.15 nfs_fasc=N 0.65 143 ms
22.04 5.15 nfs_fasc=Y 14.00 198 ms
22.04 5.19 14.00 197 ms
24.04 6.8.0-1061-aws 14.00 211 ms
26.04 7.0.0-1006-aws 14.00 155 ms
Would it be possible to forward-port the opt-in to the 22.04 HWE, 24.04 and
later
kernels? I'd be happy to help test.
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https://bugs.launchpad.net/bugs/2022098
Title:
Severe NFS performance degradation after LP #2003053
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