amd64 pmap: reduce chances that chunk mutex will be taken while pv list lock is held
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Authored by mjg on Oct 17 2019, 9:45 PM.

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alc
kib
jeff
markj

Summary

Most notably calls around get_pv_entry relock immediately after return if necessary. We can unlock upfront if we would relock later. While here change semantics of this function to allow reclamation without the lock being passed.

I did not bother benchmarking this change, but I did verify that many times things do get unlocked.

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Buildable 27092

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mjg created this revision.Oct 17 2019, 9:45 PM

Herald added a subscriber: imp. · View Herald TranscriptOct 17 2019, 9:45 PM

Harbormaster completed remote builds in B27092: Diff 63420.Oct 17 2019, 9:45 PM

mjg retitled this revision from amd64 pmap: reduce chances that chunk mutex will be taken while pv list is held to amd64 pmap: reduce chances that chunk mutex will be taken while pv list lock is held.Oct 17 2019, 9:46 PM

I find it somewhat unnatural to do this optimization unlock in pmap_try_insert_pv_entry(), at least for the case of the call from pmap_copy(). There you can release the lock much earlier while iterating of the the src page table, if it does not match the needed lock for the next pte.