linux-kernel - [PATCH 1/2] arm64: mm: vmemmap populate to page level if not section aligned

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Message-ID: <20241121071256.487220-2-quic_zhenhuah@quicinc.com>
Date: Thu, 21 Nov 2024 15:12:55 +0800
From: Zhenhua Huang <quic_zhenhuah@...cinc.com>
To: <catalin.marinas@....com>, <will@...nel.org>, <ardb@...nel.org>,
        <ryan.roberts@....com>, <mark.rutland@....com>, <joey.gouly@....com>,
        <dave.hansen@...ux.intel.com>, <akpm@...ux-foundation.org>,
        <chenfeiyang@...ngson.cn>, <chenhuacai@...nel.org>
CC: <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        Zhenhua Huang <quic_zhenhuah@...cinc.com>
Subject: [PATCH 1/2] arm64: mm: vmemmap populate to page level if not section aligned

Commit 2045a3b8911b ("mm/sparse-vmemmap: generalise vmemmap_populate_hugepages()")
optimizes the vmemmap to populate at the PMD section level. However, if start
or end is not aligned to a section boundary, such as when a subsection is hot
added, populating the entire section is inefficient and wasteful. In such
cases, it is more effective to populate at page granularity.

This change also addresses misalignment issues during vmemmap_free(). When
pmd_sect() is true, the entire PMD section is cleared, even if only a
subsection is mapped. For example, if subsections pagemap1 and pagemap2 are
added sequentially and then pagemap1 is removed, vmemmap_free() will clear the
entire PMD section, even though pagemap2 is still active.

Fixes: 2045a3b8911b ("mm/sparse-vmemmap: generalise vmemmap_populate_hugepages()")
Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
---
 arch/arm64/mm/mmu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index fe833de501f7..bfecabac14a3 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1151,7 +1151,9 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 {
 	WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));

-	if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES))
+	if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES) ||
+	!IS_ALIGNED(page_to_pfn((struct page *)start), PAGES_PER_SECTION) ||
+	!IS_ALIGNED(page_to_pfn((struct page *)end), PAGES_PER_SECTION))
 		return vmemmap_populate_basepages(start, end, node, altmap);
 	else
 		return vmemmap_populate_hugepages(start, end, node, altmap);
-- 
2.25.1