Re: [PATCH proxmox-backup 0/4] fix 7642: s3: avoid expensive uid/gid lookups

[Christian Ebner <c.ebner@proxmox.com>]

On 6/18/26 2:00 PM, Fabian Grünbichler wrote:
> On June 1, 2026 2:31 pm, Christian Ebner wrote:
>> As reported by a user in the community forum [0] and the thereof
>> resulting bugzilla entry [1], phase 2 of garbage collection currently
>> produces avoidable syscalls and parsing overhead, reading
>> /etc/nsswitch.conf and /etc/passwd for each per-chunk file locking
>> call. This is however not limited to garbage collection, but rather
>> affects per-chunk file locking in general. The backup_user() lookup
>> was identified as the culprit.
>>
>> This patch series fixes the overhead by only reading the user once at
>> the start of garbage collection or whenever a s3 backend instance is
>> created (which already performs the user lookup anyways), storing it
>> for the rest of the backend lifetime.
> 
> couldn't we implement this with less churn, and fix it for *all* call
> sites, by caching the resolved user? if it changes during the execution
> of our daemon we have a problem anyway, so might as well treat it as
> static (initialized in a lazy fashion)?
> 
> same for priv_user and backup_group..

Yes, will implement it as such then: Was unsure if acceptable to break 
with the assumption that this is no longer read on-demand, so opted for 
the less invasive approach.

But reading on-demand would be racy anyways and I see no further reason 
why this should not be treated as statically initialized.

Will adapt accordingly and send a new version.

Thanks for your feedback!