riscv: mm: hugetlb: Enable ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

Add HVO support for RISC-V; see commit 6be24be ("mm: hugetlb:
introduce a new config HUGETLB_PAGE_FREE_VMEMMAP"). This patch is
similar to commit 1e63ac0 ("arm64: mm: hugetlb: enable
HUGETLB_PAGE_FREE_VMEMMAP for arm64"), and riscv's motivation is the
same as arm64. The current riscv was ready to enable HVO after fixup,
ref commit d33deda ("riscv/mm: hugepage's PG_dcache_clean flag
is only set in head page").

See Documentation/mm/vmemmap_dedup.rst for more details.

The HugeTLB VmemmapvOptimization (HVO) defaults to off in Kconfig.

Here is the riscv test log:
cat /proc/sys/vm/hugetlb_optimize_vmemmap
echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
mount -t hugetlbfs none test/ -o pagesize=2048k
<Try some simple hugetlb test in test dir, no problem found.>

Signed-off-by: Guo Ren <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
Link: https://lore.kernel.org/linux-riscv/[email protected]/
Acked-by: Muchun Song <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: guoren83

arch/riscv/Kconfig

@@ -46,6 +46,7 @@ config RISCV
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_GENERAL_HUGETLB
+	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
 	select ARCH_WANT_LD_ORPHAN_WARN if !XIP_KERNEL
 	select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE