vm: add unlocked page lookup before trying vm_fault_soft_fast
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Authored by mjg on Mar 25 2023, 3:53 PM.

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Reviewers

kib
markj

Commits

rG0e71f4f77c01: vm: add unlocked page lookup before trying vm_fault_soft_fast

Summary

Shaves a read lock + tryupgrade trip most of the time.

Stats from doing a kernel build (counters not present in the tree):
vm.fault_soft_fast_ok: 262653
vm.fault_soft_fast_failed_other: 41
vm.fault_soft_fast_failed_no_page: 39595772
vm.fault_soft_fast_failed_page_busy: 1929
vm.fault_soft_fast_failed_page_invalid: 22183

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Repository

rG FreeBSD src repository

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Event Timeline

mjg created this revision.Mar 25 2023, 3:53 PM

Herald added a subscriber: imp. · View Herald TranscriptMar 25 2023, 3:53 PM

mjg requested review of this revision.Mar 25 2023, 3:53 PM

kib added inline comments.Mar 25 2023, 9:21 PM

sys/vm/vm_fault.c
365–366	There is no reason to busy the object if the page lookup validation fails, since you check for the busy page status in separate statement.
366–374	There should be a blank line before the multiline comment
372	And the blank line after the block of code described by the multiline comment

mjg added inline comments.Mar 25 2023, 9:37 PM

sys/vm/vm_fault.c

365–366

you mean something like this?

if (m->object != fs->first_object || m->pindex != fs->first_pindex)
        goto fail;

vm_object_busy(fs->first_object);

if (!vm_page_all_valid(m) ||
    ((fs->prot & VM_PROT_WRITE) != 0 && vm_page_busied(m)))
        goto fail_busy;

kib added inline comments.Mar 25 2023, 9:43 PM