Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove_memory() implementation

From: Wei Yang
Date: Mon Jun 03 2019 - 17:45:43 EST

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

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
>Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>Cc: Will Deacon <will.deacon@xxxxxxx>
>Cc: Mark Rutland <mark.rutland@xxxxxxx>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>Cc: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
>Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>Cc: Jun Yao <yaojun8558363@xxxxxxxxx>
>Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
>Cc: Robin Murphy <robin.murphy@xxxxxxx>
>Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> 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);
> }
>+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

Wei Yang
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