[PATCH] riscv: Use hugepage mappings for vmemmap

[PATCH] riscv: Use hugepage mappings for vmemmap

[Alexandre Ghiti]

This will allow better TLB utilization and then should be more performant.

Before:

---[ vmemmap start ]---
0xffff8d8002000000-0xffff8d8012000000    0x000000046ec00000       256M PTE .   ..     ..   D A G . . W R V
---[ vmemmap end ]---

After:

---[ vmemmap start ]---
0xffff8d8002000000-0xffff8d8012000000    0x000000046ec00000       256M PMD .   ..     ..   D A G . . W R V
---[ vmemmap end ]---

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/mm/init.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 2e011cbddf3a..f636336e6401 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1383,10 +1383,29 @@ void __init misc_mem_init(void)
 }
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
+void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
+			       unsigned long addr, unsigned long next)
+{
+	pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL);
+}
+
+int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
+				unsigned long addr, unsigned long next)
+{
+	vmemmap_verify((pte_t *)pmdp, node, addr, next);
+	return 1;
+}
+
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 			       struct vmem_altmap *altmap)
 {
-	return vmemmap_populate_basepages(start, end, node, NULL);
+	/*
+	 * Note that SPARSEMEM_VMEMMAP is only selected for rv64 and that we
+	 * can't use hugepage mappings for 2-level page table because in case of
+	 * memory hotplug, we are not able to update all the page tables with
+	 * the new PMDs.
+	 */
+	return vmemmap_populate_hugepages(start, end, node, NULL);
 }
 #endif
 
-- 
2.39.2


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Re: [PATCH] riscv: Use hugepage mappings for vmemmap

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Thu, 14 Dec 2023 14:29:35 +0100 you wrote:
> This will allow better TLB utilization and then should be more performant.
> 
> Before:
> 
> ---[ vmemmap start ]---
> 0xffff8d8002000000-0xffff8d8012000000    0x000000046ec00000       256M PTE .   ..     ..   D A G . . W R V
> 
> [...]

Here is the summary with links:
  - riscv: Use hugepage mappings for vmemmap
    https://git.kernel.org/riscv/c/ff172d4818ad

You are awesome, thank you!
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