linux-kernel - [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory

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Message-Id: <a2d91c1b5874a1217e473ffd33cd4f765a0e78b7.1601506266.git.sudaraja@codeaurora.org>
Date:   Wed, 30 Sep 2020 16:13:25 -0700
From:   Sudarshan Rajagopalan <sudaraja@...eaurora.org>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Sudarshan Rajagopalan <sudaraja@...eaurora.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Mark Rutland <mark.rutland@....com>,
        Logan Gunthorpe <logang@...tatee.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Price <steven.price@....com>
Subject: [PATCH v2] arm64/mm: add fallback option to allocate virtually contiguous memory

When section mappings are enabled, we allocate vmemmap pages from physically
continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf(). Section
mappings are good to reduce TLB pressure. But when system is highly fragmented
and memory blocks are being hot-added at runtime, its possible that such
physically continuous memory allocations can fail. Rather than failing the
memory hot-add procedure, add a fallback option to allocate vmemmap pages from
discontinuous pages using vmemmap_populate_basepages().

Signed-off-by: Sudarshan Rajagopalan <sudaraja@...eaurora.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Anshuman Khandual <anshuman.khandual@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Logan Gunthorpe <logang@...tatee.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Steven Price <steven.price@....com>
---
 arch/arm64/mm/mmu.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 75df62f..9edbbb8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1121,8 +1121,18 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 			void *p = NULL;
 
 			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
-			if (!p)
-				return -ENOMEM;
+			if (!p) {
+				if (altmap)
+					return -ENOMEM;	/* no fallback */
+
+				/*
+				 * fallback allocating with virtually
+				 * contiguous memory for this section
+				 */
+				if (vmemmap_populate_basepages(addr, next, node, NULL))
+					return -ENOMEM;
+				continue;
+			}
 
 			pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
 		} else
-- 
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