Re: [PATCH v5 1/5] mm: page_alloc: remain memblock_next_valid_pfn() on arm and arm64

[Jia He <hejianet@gmail.com>]

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 commentsA  ;-)
>
> 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
>>