mm/mempolicy: Limit policy ignored messages

[pelwell]

Reduce log spamming by limiting messages about policy changes being ignored to 5 consecutive messages per task.

[pelwell]

@popcornmix I get large numbers of these message on some systems and not others - often ps seem to be the culprit, but it's not clear what would be running that apart from some GUI element.

[popcornmix]

Just to confirm, does the spam always say Request by 'ps' to set policy to ...?
Is apt policy libnuma1 different on the "good" and "bad" system?
RPiOS trixie image with 6.12 kernel?

[pelwell]

I'll have to find the image again to be sure, but I think the answers would be "Yes", "No" and "Yes".

[popcornmix]

The reason I'm asking is this was an issue long ago where the presence of libnuma1 caused ps to try to change mempolicy.

It turned out that was unwanted (upstream) behaviour and by bumping to a newer libnuma1 resolved it. Just want to make sure we haven't lost something in our build of libnuma1 which may be the better fix for this.

[pelwell]

The two images I've found that generate the spam are both Bookworm. Updating libnuma1 from 2.0.16 to 2.0.18 does seem to have fixed it.

[pelwell]

The fact that bookworm has access to a newer version of libnuma1 without this issue means that I'm happy to close this PR.