From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
Andrew Morton <akpm@linux-foundation.org>,
Ard Biesheuvel <ardb@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
David Hildenbrand <david@redhat.com>,
Marc Zyngier <maz@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mike Rapoport <rppt@linux.ibm.com>, Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH v2 4/4] arm64: drop pfn_valid_within() and simplify pfn_valid()
Date: Wed, 21 Apr 2021 18:45:50 +0530 [thread overview]
Message-ID: <c9c4c4cc-fd4d-8bba-dd14-fa5d52161f9d@arm.com> (raw)
In-Reply-To: <YIAZYVI/HZWBr7BI@kernel.org>
On 4/21/21 5:54 PM, Mike Rapoport wrote:
> On Wed, Apr 21, 2021 at 04:36:46PM +0530, Anshuman Khandual wrote:
>>
>> On 4/21/21 12:21 PM, Mike Rapoport wrote:
>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>>
>>> The arm64's version of pfn_valid() differs from the generic because of two
>>> reasons:
>>>
>>> * Parts of the memory map are freed during boot. This makes it necessary to
>>> verify that there is actual physical memory that corresponds to a pfn
>>> which is done by querying memblock.
>>>
>>> * There are NOMAP memory regions. These regions are not mapped in the
>>> linear map and until the previous commit the struct pages representing
>>> these areas had default values.
>>>
>>> As the consequence of absence of the special treatment of NOMAP regions in
>>> the memory map it was necessary to use memblock_is_map_memory() in
>>> pfn_valid() and to have pfn_valid_within() aliased to pfn_valid() so that
>>> generic mm functionality would not treat a NOMAP page as a normal page.
>>>
>>> Since the NOMAP regions are now marked as PageReserved(), pfn walkers and
>>> the rest of core mm will treat them as unusable memory and thus
>>> pfn_valid_within() is no longer required at all and can be disabled by
>>> removing CONFIG_HOLES_IN_ZONE on arm64.
>>
>> This makes sense.
>>
>>>
>>> pfn_valid() can be slightly simplified by replacing
>>> memblock_is_map_memory() with memblock_is_memory().
>>>
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>> ---
>>> arch/arm64/Kconfig | 3 ---
>>> arch/arm64/mm/init.c | 4 ++--
>>> 2 files changed, 2 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index e4e1b6550115..58e439046d05 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -1040,9 +1040,6 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>>> def_bool y
>>> depends on NUMA
>>>
>>> -config HOLES_IN_ZONE
>>> - def_bool y
>>> -
>>
>> Right.
>>
>>> source "kernel/Kconfig.hz"
>>>
>>> config ARCH_SPARSEMEM_ENABLE
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index dc03bdc12c0f..eb3f56fb8c7c 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -243,7 +243,7 @@ int pfn_valid(unsigned long pfn)
>>>
>>> /*
>>> * ZONE_DEVICE memory does not have the memblock entries.
>>> - * memblock_is_map_memory() check for ZONE_DEVICE based
>>> + * memblock_is_memory() check for ZONE_DEVICE based
>>> * addresses will always fail. Even the normal hotplugged
>>> * memory will never have MEMBLOCK_NOMAP flag set in their
>>> * memblock entries. Skip memblock search for all non early
>>> @@ -254,7 +254,7 @@ int pfn_valid(unsigned long pfn)
>>> return pfn_section_valid(ms, pfn);
>>> }
>>> #endif
>>> - return memblock_is_map_memory(addr);
>>> + return memblock_is_memory(addr);
>>
>> Wondering if MEMBLOCK_NOMAP is now being treated similarly to other
>> memory pfns for page table walking purpose but with PageReserved(),
>> why memblock_is_memory() is still required ? At this point, should
>> not we just return valid for early_section() memory. As pfn_valid()
>> now just implies that pfn has a struct page backing which has been
>> already verified with valid_section() etc.
>
> memblock_is_memory() is required because arm64 frees unused parts of the
> memory map. So, for instance, if we have 64M out of 128M populated in a
> section the section based calculation would return 1 for a pfn in the
> second half of the section, but there would be no memory map there.
Understood.
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next prev parent reply other threads:[~2021-04-21 13:17 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-21 6:51 [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport
2021-04-21 6:51 ` [PATCH v2 1/4] include/linux/mmzone.h: add documentation for pfn_valid() Mike Rapoport
2021-04-21 10:49 ` Anshuman Khandual
2021-04-21 6:51 ` [PATCH v2 2/4] memblock: update initialization of reserved pages Mike Rapoport
2021-04-21 7:49 ` David Hildenbrand
2021-04-21 10:51 ` Anshuman Khandual
2021-04-21 6:51 ` [PATCH v2 3/4] arm64: decouple check whether pfn is in linear map from pfn_valid() Mike Rapoport
2021-04-21 10:59 ` Anshuman Khandual
2021-04-21 12:19 ` Mike Rapoport
2021-04-21 13:13 ` Anshuman Khandual
2021-04-21 6:51 ` [PATCH v2 4/4] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport
2021-04-21 7:49 ` David Hildenbrand
2021-04-21 11:06 ` Anshuman Khandual
2021-04-21 12:24 ` Mike Rapoport
2021-04-21 13:15 ` Anshuman Khandual [this message]
2021-04-22 7:00 ` [PATCH v2 0/4] " Kefeng Wang
2021-04-22 7:29 ` Mike Rapoport
2021-04-22 15:28 ` Kefeng Wang
2021-04-23 8:11 ` Kefeng Wang
2021-04-25 7:19 ` arm32: panic in move_freepages (Was [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid()) Mike Rapoport
[not found] ` <52f7d03b-7219-46bc-c62d-b976bc31ebd5@huawei.com>
2021-04-26 5:20 ` Mike Rapoport
2021-04-26 15:26 ` Kefeng Wang
2021-04-27 6:23 ` Mike Rapoport
2021-04-27 11:08 ` Kefeng Wang
2021-04-28 5:59 ` Mike Rapoport
2021-04-29 0:48 ` Kefeng Wang
2021-04-29 6:57 ` Mike Rapoport
2021-04-29 10:22 ` Kefeng Wang
2021-04-30 9:51 ` Mike Rapoport
2021-04-30 11:24 ` Kefeng Wang
2021-05-03 6:26 ` Mike Rapoport
2021-05-03 8:07 ` David Hildenbrand
2021-05-03 8:44 ` Mike Rapoport
2021-05-06 12:47 ` Kefeng Wang
2021-05-07 7:17 ` Kefeng Wang
2021-05-07 10:30 ` Mike Rapoport
2021-05-07 12:34 ` Kefeng Wang
2021-05-09 5:59 ` Mike Rapoport
2021-05-10 3:10 ` Kefeng Wang
2021-05-11 8:48 ` Mike Rapoport
2021-05-12 3:08 ` Kefeng Wang
2021-05-12 8:26 ` Mike Rapoport
2021-05-13 3:44 ` Kefeng Wang
2021-05-13 10:55 ` Mike Rapoport
2021-05-14 2:18 ` Kefeng Wang
2021-05-12 3:50 ` Matthew Wilcox
2021-04-25 6:59 ` [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport
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