📖predicate: clarify predicates don't reduce cache memory

[GellertBabel]

Clarifies in the Predicate godoc that predicates only filter which events are enqueued for reconciliation — they do not reduce what the informer cache stores. Every watched object is still held in memory regardless of whether a predicate rejects its events.

Adds a short pointer to the mechanisms that actually bound cache memory for a Kind: a label/field selector (cache.Options / cache.ByObject), a cache.ByObject Transform, or client.Options.Cache.DisableFor.

This is a source of confusion (and OOMKills) for controllers watching Kinds with many or large objects, e.g. Secrets in a namespace that also holds large, unrelated objects.

Fixes #3552

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: GellertBabel / name: Gellért Bábel (e879bd2)

[kubernetes-prow]

Welcome @GellertBabel!

It looks like this is your first PR to kubernetes-sigs/controller-runtime 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/controller-runtime has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[kubernetes-prow]

Hi @GellertBabel. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[alvaroaleman]

This first sentence just repeats the info two lines above. Please just say "This setting doesn't impact what the cache stores, use cache.Options to configure that. Keep in mind that cache.Options are global to all users of the cache." or some such.

Please do not mention individual cache option names here, they could change and are already documented in cache.Options. Suggesting to use cache.Disable for is also pretty nonsensical, you never want to disable the cache for an object you have a source configured for.

[kubernetes-prow]

LGTM label has been added.

Details

Git tree hash: 7cef5423a6c6e3a518f5c2a77668889a8401738c

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alvaroaleman, GellertBabel

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [alvaroaleman]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment