Re: v6.2 client behaviour change (repeat access calls)?

[Thorsten Leemhuis <regressions@leemhuis.info>]

On 10.03.23 11:43, Linux regression tracking (Thorsten Leemhuis) wrote:
> [CCing the regression list, as it should be in the loop for regressions:
> https://docs.kernel.org/admin-guide/reporting-regressions.html]
> 
> [also adding the author of the culprit (Trond) and the second NFS client
> maintainer (Anna) to the list of recipients]

Trond, sorry to bother you, but do you still have this regression report
on your radar? It looks a bit like it fall through the cracks, as I
don't see any reply since it was posted nearly two weeks ago. Or did
some progress to address this happen and I just missed it?

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

#regzbot poke

> [TLDR: I'm adding this report to the list of tracked Linux kernel
> regressions; the text you find below is based on a few templates
> paragraphs you might have encountered already in similar form.
> See link in footer if these mails annoy you.]
> 
> On 07.03.23 18:38, Daire Byrne wrote:
>> I noticed a change in behaviour in the v6.2.x client versus v6.1.12 (and below).
>>
>> We have some servers that mount Netapps from different locations many
>> milliseconds away, and these contain apps and libs that get added to
>> the LD_LIBRARY_PATH and PATH on remote login.
>>
>> I then noticed that when I ssh'd into a remote server that had these
>> mounts and the shell was starting, the first login was normal and I
>> observed an expected flurry of lookups,getattrs and access calls for a
>> grand total of only ~120 packets to the Netapp.
>>
>> But when I disconnect and reconnect (ssh), now I see a flood of access
>> calls to the netapp for a handful of repeating filehandles which look
>> something like:
>>
>>  2700 85.942563180 10.23.112.10 → 10.23.21.11  NFS 254 V3 ACCESS Call,
>> FH: 0x7f36addc, [Check: RD LU MD XT DL]
>>  2701 85.999838796  10.23.21.11 → 10.23.112.10 NFS 190 V3 ACCESS Reply
>> (Call In 2700), [Allowed: RD LU MD XT DL]
>>  2702 85.999970825 10.23.112.10 → 10.23.21.11  NFS 254 V3 ACCESS Call,
>> FH: 0x7f36addc, [Check: RD LU MD XT DL]
>>  2703 86.055340946  10.23.21.11 → 10.23.112.10 NFS 190 V3 ACCESS Reply
>> (Call In 2702), [Allowed: RD LU MD XT DL]
>>  2704 86.056865308 10.23.112.10 → 10.23.21.11  NFS 254 V3 ACCESS Call,
>> FH: 0x7f36addc, [Check: RD LU MD XT DL]
>>  2705 86.112233415  10.23.21.11 → 10.23.112.10 NFS 190 V3 ACCESS Reply
>> (Call In 2704), [Allowed: RD LU MD XT DL]
>>
>> This time we total 5000+ packets for this login which becomes very
>> noticeable when the Netapp is 50ms away.
>>
>> I didn't understand why the first login was fine but the second goes
>> into this repeating access pattern. I set actimeo=3600 (long) but it
>> does not seem to affect it.
>>
>> I do not see this prior to v6.2 where repeated logins are equally fast
>> and we don't see the repeating access calls.
>>
>> So a bit of digging through the v6.2 changes and this looked like the
>> relevant change:
>>
>> commit 0eb43812c027 ("NFS: Clear the file access cache upon login”)
>> [PATCH] NFS: Judge the file access cache's timestamp in rcu path?
>>
>> I reverted those and got the prior (v6.1) performance.
>>
>> What constitutes a login exactly? I also have services like "sysstat"
>> or pcp that cause a systemd-logind to trigger regularly on our
>> machines.... does that count and invalidate the cache?
>>
>> Do the repeated access calls on the same handful of filehandles make
>> sense? Even prior to those patches (or v6.1) there are only a couple
>> of ACCESS calls to the Netapp on login.
>>
>> We are a bit unique in that we run quite a few WAN high latency NFS
>> workflows so are happy to trade long lived caches (e.g. actimeo and
>> even nocto on occasion) for lower ops at the expense of total
>> correctness.
> 
> Thanks for the report. To be sure the issue doesn't fall through the
> cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
> tracking bot:
> 
> #regzbot ^introduced 0eb43812c027
> #regzbot title nfs: flood of access on second log-in (first is fine)
> #regzbot ignore-activity
> 
> This isn't a regression? This issue or a fix for it are already
> discussed somewhere else? It was fixed already? You want to clarify when
> the regression started to happen? Or point out I got the title or
> something else totally wrong? Then just reply and tell me -- ideally
> while also telling regzbot about it, as explained by the page listed in
> the footer of this mail.
> 
> Developers: When fixing the issue, remember to add 'Link:' tags pointing
> to the report (the parent of this mail). See page linked in footer for
> details.
> 
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> --
> Everything you wanna know about Linux kernel regression tracking:
> https://linux-regtracking.leemhuis.info/about/#tldr
> That page also explains what to do if mails like this annoy you.