From: Oscar Salvador <osalvador@suse.de>
To: Zhenhua Huang <quic_zhenhuah@quicinc.com>
Cc: anshuman.khandual@arm.com, catalin.marinas@arm.com,
david@redhat.com, will@kernel.org, ardb@kernel.org,
ryan.roberts@arm.com, mark.rutland@arm.com, joey.gouly@arm.com,
dave.hansen@linux.intel.com, akpm@linux-foundation.org,
chenfeiyang@loongson.cn, chenhuacai@kernel.org,
linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, quic_tingweiz@quicinc.com,
stable@vger.kernel.org
Subject: Re: [PATCH v9] arm64: mm: Populate vmemmap at the page level if not section aligned
Date: Tue, 4 Mar 2025 09:22:09 +0100 [thread overview]
Message-ID: <Z8a4MWPpTKm2FAce@localhost.localdomain> (raw)
In-Reply-To: <20250304072700.3405036-1-quic_zhenhuah@quicinc.com>
On Tue, Mar 04, 2025 at 03:27:00PM +0800, Zhenhua Huang wrote:
> On the arm64 platform with 4K base page config, SECTION_SIZE_BITS is set
> to 27, making one section 128M. The related page struct which vmemmap
> points to is 2M then.
> Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the
> vmemmap to populate at the PMD section level which was suitable
> initially since hot plug granule is always one section(128M). However,
> commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> introduced a 2M(SUBSECTION_SIZE) hot plug granule, which disrupted the
> existing arm64 assumptions.
>
> The first problem is that if start or end is not aligned to a section
> boundary, such as when a subsection is hot added, populating the entire
> section is wasteful.
>
> The next problem is if we hotplug something that spans part of 128 MiB
> section (subsections, let's call it memblock1), and then hotplug something
> that spans another part of a 128 MiB section(subsections, let's call it
> memblock2), and subsequently unplug memblock1, vmemmap_free() will clear
> the entire PMD entry which also supports memblock2 even though memblock2
> is still active.
>
> Assuming hotplug/unplug sizes are guaranteed to be symmetric. Do the
> fix similar to x86-64: populate to pages levels if start/end is not aligned
> with section boundary.
>
> Cc: <stable@vger.kernel.org> # v5.4+
> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE Labs
next prev parent reply other threads:[~2025-03-04 9:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-04 7:27 [PATCH v9] arm64: mm: Populate vmemmap at the page level if not section aligned Zhenhua Huang
2025-03-04 8:22 ` Oscar Salvador [this message]
2025-03-05 18:59 ` Catalin Marinas
2025-03-11 13:13 ` Will Deacon
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