vm_page: Use atomic loads for cmpset loops
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Authored by markj on Oct 4 2024, 3:07 PM.

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Reviewers

alc
kib
dougm

Commits

rG94e5ec7f869e: vm_page: Use atomic loads for cmpset loops
rGd8b32da2354d: vm_page: Use atomic loads for cmpset loops

Summary

Make sure that the compiler loads the initial value value only once.
Because atomic_fcmpset is used to load the value for subsequent
iterations, this is probably not needed, but we should not rely on that.

I verified that code generated for an amd64 GENERIC kernel does not
change.

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rG FreeBSD src repository

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Event Timeline

markj created this revision.Oct 4 2024, 3:07 PM

Herald added a subscriber: imp. · View Herald TranscriptOct 4 2024, 3:07 PM

Harbormaster completed remote builds in B59757: Diff 144250.Oct 4 2024, 3:07 PM

markj requested review of this revision.Oct 4 2024, 3:07 PM

markj added a parent revision: D46942: vm_map: Record the maximum size of the map over time.

markj added a child revision: D46944: vm_page: Fix a logic bug in vm_page_unwire_managed().

kib accepted this revision.Oct 4 2024, 3:31 PM

This revision is now accepted and ready to land.Oct 4 2024, 3:31 PM

alc accepted this revision.Oct 4 2024, 3:39 PM

dougm added inline comments.Oct 4 2024, 4:04 PM

sys/vm/vm_page.c
5275	What about here?

markj added inline comments.Oct 4 2024, 4:09 PM

sys/vm/vm_page.c
5275	I don't see any need to here, since the value is not used before it's passed to atomic_fcmpset. Or, in the last case in this function, it's loaded only once.