KVM: x86/mmu: Track tail count in pte_list_desc to optimize guest fork()

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Rework "struct pte_list_desc" and pte_list_{add|remove} to track the tail
count, i.e. number of PTEs in non-head descriptors, and to always keep all
tail descriptors full so that adding a new entry and counting the number
of entries is done in constant time instead of linear time.

No visible performace is changed in tests.  But pte_list_add() is no longer
shown in the perf result for the COWed pages even the guest forks millions
of tasks.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230113122910.672417-1-jiangshanlai@gmail.com
[sean: reword shortlog, tweak changelog, add lots of comments, add BUG_ON()]
Signed-off-by: Sean Christopherson <seanjc@google.com>

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Lai Jiangshan 2023-01-13 20:29:10 +08:00 • committed by Sean Christopherson

parent 19ace7d6ca

commit 141705b783

1 changed files with 65 additions and 44 deletions

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arch/x86/kvm/mmu/mmu.c

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