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Subject[PATCH 2/5] arm64: mremap speedup - Enable HAVE_MOVE_PMD
From
HAVE_MOVE_PMD enables remapping pages at the PMD level if both the
source and destination addresses are PMD-aligned.

HAVE_MOVE_PMD is already enabled on x86. The original patch [1] that
introduced this config did not enable it on arm64 at the time because
of performance issues with flushing the TLB on every PMD move. These
issues have since been addressed in more recent releases with
improvements to the arm64 TLB invalidation and core mmu_gather code as
Will Deacon mentioned in [2].

From the data below, it can be inferred that there is approximately
8x improvement in performance when HAVE_MOVE_PMD is enabled on arm64.

--------- Test Results ----------

The following results were obtained on an arm64 device running a 5.4
kernel, by remapping a PMD-aligned, 1GB sized region to a PMD-aligned
destination. The results from 10 iterations of the test are given below.
All times are in nanoseconds.

Control HAVE_MOVE_PMD

9220833 1247761
9002552 1219896
9254115 1094792
8725885 1227760
9308646 1043698
9001667 1101771
8793385 1159896
8774636 1143594
9553125 1025833
9374010 1078125

9100885.4 1134312.6 <-- Mean Time in nanoseconds

Total mremap time for a 1GB sized PMD-aligned region drops from
~9.1 milliseconds to ~1.1 milliseconds. (~8x speedup).

[1] https://lore.kernel.org/r/20181108181201.88826-3-joelaf@google.com
[2] https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg140837.html

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
arch/arm64/Kconfig | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6d232837cbee..844d089668e3 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -121,6 +121,7 @@ config ARM64
select GENERIC_VDSO_TIME_NS
select HANDLE_DOMAIN_IRQ
select HARDIRQS_SW_RESEND
+ select HAVE_MOVE_PMD
select HAVE_PCI
select HAVE_ACPI_APEI if (ACPI && EFI)
select HAVE_ALIGNED_STRUCT_PAGE if SLUB
--
2.28.0.709.gb0816b6eb0-goog
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