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

From: Ard Biesheuvel
Date: Mon Apr 02 2018 - 02:56:08 EST

On 2 April 2018 at 04:30, Jia He <hejianet@xxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Jia He <jia.he@xxxxxxxxxxxxxxxx>

Hello Jia,

Apologies for chiming in late.

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
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?


> ---
> 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
>