From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Hubert Ralf <Ralf.Hubert@preh.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] aarch64/mm: speedup memory initialisation
Date: Thu, 12 Sep 2019 14:29:49 +0530 [thread overview]
Message-ID: <7ac85677-782a-5080-558f-bc210b5aad10@arm.com> (raw)
In-Reply-To: <bf14a3cb2812c03d08c380fccc4ca336cb7b5352.camel@preh.de>
On 09/12/2019 02:10 PM, Hubert Ralf wrote:
> Am Donnerstag, den 12.09.2019, 13:42 +0530 schrieb Anshuman Khandual:
>>
>> On 09/10/2019 02:29 PM, Hubert Ralf wrote:
>>> On ARM64 memmap_init_zone is used during bootmem_init, which iterates over
>>> all pages in the memory starting at the lowest address until the highest
>>> address is reached. On arm64 this ends up in searching a memmory region
>>> containing for each single page between lowest and highest available
>>> physicall address.
>>>
>>> Having a sparse memory system there may be some big holes in the
>>> memory map. For each page in this holes a lookup is done, which is
>>> implemented as a binary search on the available memory blocks.
>>>
>>> Adding a memmap_init for aarch64 to do the init only for the available
>>> memory areas reduces the time needed for initialising memory on startup.
>>> On a Renesas R-CAR M3 based system with a total hole of 20GB bootmem_init
>>> execution time is reduced from 378ms to 84ms.
>>>
>>> Signed-off-by: Ralf Hubert <ralf.hubert@preh.de>
>>> ---
>>> arch/arm64/include/asm/pgtable.h | 7 +++++++
>>> arch/arm64/mm/init.c | 24 ++++++++++++++++++++++++
>>> 2 files changed, 31 insertions(+)
>>>
>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>>> index e09760ece844..8c6eefc08b0b 100644
>>> --- a/arch/arm64/include/asm/pgtable.h
>>> +++ b/arch/arm64/include/asm/pgtable.h
>>> @@ -298,6 +298,13 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b)
>>> return (lhs == rhs);
>>> }
>>>
>>> +#ifdef CONFIG_SPARSEMEM
>>> +/* arch mem_map init routine is needed due to holes in a memmap */
>>> +# define __HAVE_ARCH_MEMMAP_INIT
>>
>> This is not required any more. Its gone with the following commit which
>> also made generic memmap_init() an weak function currently overridden
>> only on ia64.
>>
>> dfb3ccd00a0 ("mm: make memmap_init a proper function")
>>
>>> + void memmap_init(unsigned long size, int nid, unsigned long zone,
>>> + unsigned long start_pfn);
>>> +#endif /* CONFIG_SPARSEMEM */
>>> +
>>> /*
>>> * Huge pte definitions.
>>> */
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index f3c795278def..206b28310872 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -250,6 +250,30 @@ int pfn_valid(unsigned long pfn)
>>> }
>>> EXPORT_SYMBOL(pfn_valid);
>>>
>>> +#ifdef CONFIG_SPARSEMEM
>>> +void __meminit
>>> +memmap_init(unsigned long size, int nid, unsigned long zone,
>>> + unsigned long start_pfn)
>>> +{
>>> + struct memblock_region *reg;
>>> +
>>> + for_each_memblock(memory, reg) {
>>> + unsigned long start = memblock_region_memory_base_pfn(reg);
>>> + unsigned long end = memblock_region_memory_end_pfn(reg);
>>> +
>>> + if (start < start_pfn)
>>> + start = start_pfn;
>>> + if (end > start_pfn + size)
>>> + end = start_pfn + size;
>>> +
>>> + if (start < end) {
>>> + memmap_init_zone(end - start, nid, zone, start,
>>> + MEMMAP_EARLY, NULL);
>>> + }
>>> + }
>>> +}
>>> +#endif /* CONFIG_SPARSEMEM */
>>
>> In generic mmap_init(), the current high cost comes from early_pfn_valid()
>> check for each pfn in memmap_init_zone() given that early_pfn_valid() is
>> pfn_valid() when CONFIG_SPARSEMEM which is known to be expensive on arm64.
>>
>> Though we cannot do anything about pfns which are really present but the
>> high cost for non present pfns should be eliminated. The following check
>> in the above for_each_memblock() loop can achieve that.
>>
>> if (reg->flags & MEMBLOCK_NOMAP)
>> continue;
>>
>> MEMBLOCK_NOMAP universally should not be initialized into a zone and holes
>> if any should also be universally skipped across platforms. So these changes
>> can be moved into generic memmap_init() which will benefit other platforms.
> Not sure if I got this. This is a additional short path for memblocks with
> the MEMBLOCK_NOMAP flag set, right? For memblocks without these flag the remaining
> code still needs to be executed?
Right, they should be initialized in the zone.
>
> In my case I have 4 memblocks with 1.5GB RAM at 0x4000 0000, 0x4 8000 0000,
> 0x6 0000 0000 and 0x6 8000 0000. None of them has the MEMBLOCK_NOMAP flag set.
All of them should be added into the zone with memmap_init_zone() because none of
them has the flag.
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prev parent reply other threads:[~2019-09-12 8:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-10 8:59 [PATCH] aarch64/mm: speedup memory initialisation Hubert Ralf
2019-09-10 13:07 ` Robin Murphy
2019-09-11 16:22 ` James Morse
2019-09-12 5:36 ` Hubert Ralf
2019-09-12 8:12 ` Anshuman Khandual
2019-09-12 8:40 ` Hubert Ralf
2019-09-12 8:59 ` Anshuman Khandual [this message]
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