Re: [v3 3/4] memblock: introduce MEMBLOCK_RSRV_NOINIT_VMEMMAP flag

[Mike Rapoport <rppt@kernel.org>]

On Fri, Aug 25, 2023 at 12:18:35PM +0100, Usama Arif wrote:
> For reserved memory regions marked with this flag,
> reserve_bootmem_region is not called during memmap_init_reserved_pages.
> This can be used to avoid struct page initialization for
> regions which won't need them, for e.g. hugepages with
> HVO enabled.
> 
> Signed-off-by: Usama Arif <usama.arif@bytedance.com>
> ---
>  include/linux/memblock.h | 10 ++++++++++
>  mm/memblock.c            | 32 +++++++++++++++++++++++++++-----
>  2 files changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index f71ff9f0ec81..6d681d053880 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -40,6 +40,8 @@ extern unsigned long long max_possible_pfn;
>   * via a driver, and never indicated in the firmware-provided memory map as
>   * system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the
>   * kernel resource tree.
> + * @MEMBLOCK_RSRV_NOINIT_VMEMMAP: memory region for which struct pages are
> + * not initialized (only for reserved regions).
>   */
>  enum memblock_flags {
>  	MEMBLOCK_NONE		= 0x0,	/* No special request */
> @@ -47,6 +49,8 @@ enum memblock_flags {
>  	MEMBLOCK_MIRROR		= 0x2,	/* mirrored region */
>  	MEMBLOCK_NOMAP		= 0x4,	/* don't add to kernel direct mapping */
>  	MEMBLOCK_DRIVER_MANAGED = 0x8,	/* always detected via a driver */
> +	/* don't initialize struct pages associated with this reserver memory block */
> +	MEMBLOCK_RSRV_NOINIT_VMEMMAP	= 0x10,

The flag means that struct page shouldn't be initialized, it may be used
not only by vmemmap optimizations.
Please drop _VMEMMAP.

And I agree with Muchun's remarks about the comments.



>  };
>  
>  /**
> @@ -125,6 +129,7 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
>  int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
>  int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
>  int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
> +int memblock_reserved_mark_noinit_vmemmap(phys_addr_t base, phys_addr_t size);

memblock does not care about vmemmap, please drop _vmemmap here and below as well.
  
>  void memblock_free_all(void);
>  void memblock_free(void *ptr, size_t size);
> @@ -259,6 +264,11 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
>  	return m->flags & MEMBLOCK_NOMAP;
>  }
>  
> +static inline bool memblock_is_noinit_vmemmap(struct memblock_region *m)

memblock_is_reserved_noinit please.

> +{
> +	return m->flags & MEMBLOCK_RSRV_NOINIT_VMEMMAP;
> +}
> +
>  static inline bool memblock_is_driver_managed(struct memblock_region *m)
>  {
>  	return m->flags & MEMBLOCK_DRIVER_MANAGED;
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 43cb4404d94c..a9782228c840 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -991,6 +991,23 @@ int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
>  	return memblock_setclr_flag(&memblock.memory, base, size, 0, MEMBLOCK_NOMAP);
>  }
>  
> +/**
> + * memblock_reserved_mark_noinit_vmemmap - Mark a reserved memory region with flag
> + * MEMBLOCK_RSRV_NOINIT_VMEMMAP.

this should be about what marking RSRV_NOINIT does, not what flag it uses

> + * @base: the base phys addr of the region
> + * @size: the size of the region
> + *
> + * struct pages will not be initialized for reserved memory regions marked with
> + * %MEMBLOCK_RSRV_NOINIT_VMEMMAP.
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +int __init_memblock memblock_reserved_mark_noinit_vmemmap(phys_addr_t base, phys_addr_t size)
> +{
> +	return memblock_setclr_flag(&memblock.reserved, base, size, 1,
> +				    MEMBLOCK_RSRV_NOINIT_VMEMMAP);
> +}
> +
>  static bool should_skip_region(struct memblock_type *type,
>  			       struct memblock_region *m,
>  			       int nid, int flags)
> @@ -2107,13 +2124,18 @@ static void __init memmap_init_reserved_pages(void)
>  		memblock_set_node(start, end, &memblock.reserved, nid);
>  	}
>  
> -	/* initialize struct pages for the reserved regions */
> +	/*
> +	 * initialize struct pages for reserved regions that don't have
> +	 * the MEMBLOCK_RSRV_NOINIT_VMEMMAP flag set
> +	 */
>  	for_each_reserved_mem_region(region) {
> -		nid = memblock_get_region_node(region);
> -		start = region->base;
> -		end = start + region->size;
> +		if (!memblock_is_noinit_vmemmap(region)) {
> +			nid = memblock_get_region_node(region);
> +			start = region->base;
> +			end = start + region->size;
>  
> -		reserve_bootmem_region(start, end, nid);
> +			reserve_bootmem_region(start, end, nid);
> +		}
>  	}
>  }
>  
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.