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SubjectRe: [PATCH v5 1/5] mm: page_alloc: remain memblock_next_valid_pfn() on arm and arm64
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On 4/2/2018 2:55 PM, Ard Biesheuvel Wrote:
> On 2 April 2018 at 04:30, Jia He <hejianet@gmail.com> wrote:
>> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
>> where possible") optimized the loop in memmap_init_zone(). But it causes
>> possible panic bug. So Daniel Vacek reverted it later.
>>
>> But as suggested by Daniel Vacek, it is fine to using memblock to skip
>> gaps and finding next valid frame with CONFIG_HAVE_ARCH_PFN_VALID.
>>
>> On arm and arm64, memblock is used by default. But generic version of
>> pfn_valid() is based on mem sections and memblock_next_valid_pfn() does
>> not always return the next valid one but skips more resulting in some
>> valid frames to be skipped (as if they were invalid). And that's why
>> kernel was eventually crashing on some !arm machines.
>>
>> And as verified by Eugeniu Rosca, arm can benifit from commit
>> b92df1de5d28. So remain the memblock_next_valid_pfn on arm{,64} and move
>> the related codes to arm64 arch directory.
>>
>> Suggested-by: Daniel Vacek <neelx@redhat.com>
>> Signed-off-by: Jia He <jia.he@hxt-semitech.com>
> Hello Jia,
>
> Apologies for chiming in late.
no problem, thanks for your comments  ;-)
>
> If we are going to rearchitect this, I'd rather we change the loop in
> memmap_init_zone() so that we skip to the next valid PFN directly
> rather than skipping to the last invalid PFN so that the pfn++ in the
hmm... Maybe this macro name makes you confused

pfn = skip_to_last_invalid_pfn(pfn);

how about skip_to_next_valid_pfn?

> for () results in the next value. Can we replace the pfn++ there with
> a function calls that defaults to 'return pfn + 1', but does the skip
> for architectures that implement it?
I am not sure I understand your question here.
With this patch, on !arm arches, skip_to_last_invalid_pfn is equal to
(pfn), and will be increased
when for{} loop continue. We only *skip* to the start pfn of next valid
region when
CONFIG_HAVE_MEMBLOCK and CONFIG_HAVE_ARCH_PFN_VALID(arm/arm64 supports
both).


--
Cheers,
Jia

>
>
>> ---
>> arch/arm/include/asm/page.h | 2 ++
>> arch/arm/mm/init.c | 31 ++++++++++++++++++++++++++++++-
>> arch/arm64/include/asm/page.h | 2 ++
>> arch/arm64/mm/init.c | 31 ++++++++++++++++++++++++++++++-
>> include/linux/mmzone.h | 1 +
>> mm/page_alloc.c | 4 +++-
>> 6 files changed, 68 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
>> index 4355f0e..489875c 100644
>> --- a/arch/arm/include/asm/page.h
>> +++ b/arch/arm/include/asm/page.h
>> @@ -158,6 +158,8 @@ typedef struct page *pgtable_t;
>>
>> #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>> extern int pfn_valid(unsigned long);
>> +extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
>> +#define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
>> #endif
>>
>> #include <asm/memory.h>
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index a1f11a7..0fb85ca 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>> @@ -198,7 +198,36 @@ int pfn_valid(unsigned long pfn)
>> return memblock_is_map_memory(__pfn_to_phys(pfn));
>> }
>> EXPORT_SYMBOL(pfn_valid);
>> -#endif
>> +
>> +/* HAVE_MEMBLOCK is always enabled on arm */
>> +unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>> +{
>> + struct memblock_type *type = &memblock.memory;
>> + unsigned int right = type->cnt;
>> + unsigned int mid, left = 0;
>> + phys_addr_t addr = PFN_PHYS(++pfn);
>> +
>> + do {
>> + mid = (right + left) / 2;
>> +
>> + if (addr < type->regions[mid].base)
>> + right = mid;
>> + else if (addr >= (type->regions[mid].base +
>> + type->regions[mid].size))
>> + left = mid + 1;
>> + else {
>> + /* addr is within the region, so pfn is valid */
>> + return pfn;
>> + }
>> + } while (left < right);
>> +
>> + if (right == type->cnt)
>> + return -1UL;
>> + else
>> + return PHYS_PFN(type->regions[right].base);
>> +}
>> +EXPORT_SYMBOL(memblock_next_valid_pfn);
>> +#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
>>
>> #ifndef CONFIG_SPARSEMEM
>> static void __init arm_memory_present(void)
>> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
>> index 60d02c8..e57d3f2 100644
>> --- a/arch/arm64/include/asm/page.h
>> +++ b/arch/arm64/include/asm/page.h
>> @@ -39,6 +39,8 @@ typedef struct page *pgtable_t;
>>
>> #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>> extern int pfn_valid(unsigned long);
>> +extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
>> +#define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
>> #endif
>>
>> #include <asm/memory.h>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 00e7b90..13e43ff 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -290,7 +290,36 @@ int pfn_valid(unsigned long pfn)
>> return memblock_is_map_memory(pfn << PAGE_SHIFT);
>> }
>> EXPORT_SYMBOL(pfn_valid);
>> -#endif
>> +
>> +/* HAVE_MEMBLOCK is always enabled on arm64 */
>> +unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>> +{
>> + struct memblock_type *type = &memblock.memory;
>> + unsigned int right = type->cnt;
>> + unsigned int mid, left = 0;
>> + phys_addr_t addr = PFN_PHYS(++pfn);
>> +
>> + do {
>> + mid = (right + left) / 2;
>> +
>> + if (addr < type->regions[mid].base)
>> + right = mid;
>> + else if (addr >= (type->regions[mid].base +
>> + type->regions[mid].size))
>> + left = mid + 1;
>> + else {
>> + /* addr is within the region, so pfn is valid */
>> + return pfn;
>> + }
>> + } while (left < right);
>> +
>> + if (right == type->cnt)
>> + return -1UL;
>> + else
>> + return PHYS_PFN(type->regions[right].base);
>> +}
>> +EXPORT_SYMBOL(memblock_next_valid_pfn);
>> +#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
>>
>> #ifndef CONFIG_SPARSEMEM
>> static void __init arm64_memory_present(void)
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index d797716..f9c0c46 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -1245,6 +1245,7 @@ static inline int pfn_valid(unsigned long pfn)
>> return 0;
>> return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
>> }
>> +#define skip_to_last_invalid_pfn(pfn) (pfn)
>> #endif
>>
>> static inline int pfn_present(unsigned long pfn)
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c19f5ac..30f7d76 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5483,8 +5483,10 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>> if (context != MEMMAP_EARLY)
>> goto not_early;
>>
>> - if (!early_pfn_valid(pfn))
>> + if (!early_pfn_valid(pfn)) {
>> + pfn = skip_to_last_invalid_pfn(pfn);
>> continue;
>> + }
>> if (!early_pfn_in_nid(pfn, nid))
>> continue;
>> if (!update_defer_init(pgdat, pfn, end_pfn, &nr_initialised))
>> --
>> 2.7.4
>>

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