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

From: Wei Yang <richard.weiyang@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
	Dan Williams <dan.j.williams@intel.com>,
	Wei Yang <richard.weiyang@gmail.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Chintan Pandya <cpandya@codeaurora.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Jun Yao <yaojun8558363@gmail.com>, Yu Zhao <yuzhao@google.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH v3 04/11] arm64/mm: Add temporary arch_remove_memory() implementation
Date: Mon, 3 Jun 2019 21:41:39 +0000	[thread overview]
Message-ID: <20190603214139.mercn5hol2yyfl2s@master> (raw)
In-Reply-To: <20190527111152.16324-5-david@redhat.com>

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@arm.com>
>Cc: Will Deacon <will.deacon@arm.com>
>Cc: Mark Rutland <mark.rutland@arm.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>Cc: Chintan Pandya <cpandya@codeaurora.org>
>Cc: Mike Rapoport <rppt@linux.ibm.com>
>Cc: Jun Yao <yaojun8558363@gmail.com>
>Cc: Yu Zhao <yuzhao@google.com>
>Cc: Robin Murphy <robin.murphy@arm.com>
>Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>Signed-off-by: David Hildenbrand <david@redhat.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
Help you, Help me