linux-kernel - Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove

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Date:   Mon, 3 Jun 2019 21:41:39 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        Dan Williams <dan.j.williams@...el.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Jun Yao <yaojun8558363@...il.com>, Yu Zhao <yuzhao@...gle.com>,
        Robin Murphy <robin.murphy@....com>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove_memory()
 implementation

On Mon, May 27, 2019 at 01:11:45PM +0200, David Hildenbrand wrote:
>A proper arch_remove_memory() implementation is on its way, which also
>cleanly removes page tables in arch_add_memory() in case something goes
>wrong.

Would this be better to understand?

    removes page tables created in arch_add_memory

>
>As we want to use arch_remove_memory() in case something goes wrong
>during memory hotplug after arch_add_memory() finished, let's add
>a temporary hack that is sufficient enough until we get a proper
>implementation that cleans up page table entries.
>
>We will remove CONFIG_MEMORY_HOTREMOVE around this code in follow up
>patches.
>
>Cc: Catalin Marinas <catalin.marinas@....com>
>Cc: Will Deacon <will.deacon@....com>
>Cc: Mark Rutland <mark.rutland@....com>
>Cc: Andrew Morton <akpm@...ux-foundation.org>
>Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>Cc: Chintan Pandya <cpandya@...eaurora.org>
>Cc: Mike Rapoport <rppt@...ux.ibm.com>
>Cc: Jun Yao <yaojun8558363@...il.com>
>Cc: Yu Zhao <yuzhao@...gle.com>
>Cc: Robin Murphy <robin.murphy@....com>
>Cc: Anshuman Khandual <anshuman.khandual@....com>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> arch/arm64/mm/mmu.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
>diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>index a1bfc4413982..e569a543c384 100644
>--- a/arch/arm64/mm/mmu.c
>+++ b/arch/arm64/mm/mmu.c
>@@ -1084,4 +1084,23 @@ int arch_add_memory(int nid, u64 start, u64 size,
> 	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
> 			   restrictions);
> }
>+#ifdef CONFIG_MEMORY_HOTREMOVE
>+void arch_remove_memory(int nid, u64 start, u64 size,
>+			struct vmem_altmap *altmap)
>+{
>+	unsigned long start_pfn = start >> PAGE_SHIFT;
>+	unsigned long nr_pages = size >> PAGE_SHIFT;
>+	struct zone *zone;
>+
>+	/*
>+	 * FIXME: Cleanup page tables (also in arch_add_memory() in case
>+	 * adding fails). Until then, this function should only be used
>+	 * during memory hotplug (adding memory), not for memory
>+	 * unplug. ARCH_ENABLE_MEMORY_HOTREMOVE must not be
>+	 * unlocked yet.
>+	 */
>+	zone = page_zone(pfn_to_page(start_pfn));

Compared with arch_remove_memory in x86. If altmap is not NULL, zone will be
retrieved from page related to altmap. Not sure why this is not the same?

>+	__remove_pages(zone, start_pfn, nr_pages, altmap);
>+}
>+#endif
> #endif
>-- 
>2.20.1

-- 
Wei Yang
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