Le 10/07/2023 à 18:08, Aneesh Kumar K.V a écrit :
> dax vmemmap optimization requires a minimum of 2 PAGE_SIZE area within
> vmemmap such that tail page mapping can point to the second PAGE_SIZE area.
> Enforce that in vmemmap_can_optimize() function.
>
> Architectures like powerpc also want to enable vmemmap optimization
> conditionally (only with radix MMU translation). Hence allow architecture
> override.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Why renaming vmemmap_can_optimize() to __vmemmap_can_optimize() and keep
it when vmemmap_can_optimize() has been override ? Is that because you
expect overriding version of vmemmap_can_optimize() to call
__vmemmap_can_optimize() ?
> ---
> include/linux/mm.h | 27 +++++++++++++++++++++++----
> mm/mm_init.c | 2 +-
> 2 files changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2dd73e4f3d8e..1a2234ee14d2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3639,13 +3639,32 @@ void vmemmap_free(unsigned long start, unsigned long end,
> struct vmem_altmap *altmap);
> #endif
>
> +#define VMEMMAP_RESERVE_NR 2
> #ifdef CONFIG_ARCH_WANT_OPTIMIZE_VMEMMAP
> -static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
> - struct dev_pagemap *pgmap)
> +static inline bool __vmemmap_can_optimize(struct vmem_altmap *altmap,
> + struct dev_pagemap *pgmap)
> {
> - return is_power_of_2(sizeof(struct page)) &&
> - pgmap && (pgmap_vmemmap_nr(pgmap) > 1) && !altmap;
> + unsigned long nr_pages;
> + unsigned long nr_vmemmap_pages;
> +
> + if (!pgmap || !is_power_of_2(sizeof(struct page)))
> + return false;
> +
> + nr_pages = pgmap_vmemmap_nr(pgmap);
> + nr_vmemmap_pages = ((nr_pages * sizeof(struct page)) >> PAGE_SHIFT);
> + /*
> + * For vmemmap optimization with DAX we need minimum 2 vmemmap
> + * pages. See layout diagram in Documentation/mm/vmemmap_dedup.rst
> + */
> + return !altmap && (nr_vmemmap_pages > VMEMMAP_RESERVE_NR);
> }
> +/*
> + * If we don't have an architecture override, use the generic rule
> + */
> +#ifndef vmemmap_can_optimize
> +#define vmemmap_can_optimize __vmemmap_can_optimize
> +#endif
> +
> #else
> static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
> struct dev_pagemap *pgmap)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index a1963c3322af..245ac69b66a5 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1020,7 +1020,7 @@ static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
> if (!vmemmap_can_optimize(altmap, pgmap))
> return pgmap_vmemmap_nr(pgmap);
>
> - return 2 * (PAGE_SIZE / sizeof(struct page));
> + return VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page));
> }
>
> static void __ref memmap_init_compound(struct page *head,
