Memory hotplug locking issue: Useless (?) zone span seqlock

Mathieu Desnoyers
2025-03-07T20:22:35Z

I'm currently perfecting my understanding of the mm code and reviewing
pieces of it as I go, and stumbled on this:

commit 27cacaad16c5 ("mm,memory_hotplug: drop unneeded locking")

This commit removes all users of zone_span_writelock(), thus making
the inline useless, but leaves the now useless
zone_span_seqbegin()/zone_span_seqretry() in place within
page_outside_zone_boundaries().

So I'm confused. What's going on ?

And if this commit got things very wrong when removing the
seqlock, I wonder if there are cases where its partial
pgdat_resize_lock() removal can be an issue as well.

Thanks,

Mathieu

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Mathieu Desnoyers
EfficiOS Inc.