Re: [RFC PATCH] page_ext: create page extension for all memblock memory regions

[Andrew Morton <akpm@linux-foundation.org>]

On Mon,  9 May 2022 16:43:30 +0900 Jaewon Kim <jaewon31.kim@samsung.com> wrote:

> The page extension can be prepared for each section. But if the first
> page is not valid, the page extension for the section was not
> initialized though there were many other valid pages within the section.
> 
> To support the page extension for all sections, refer to memblock memory
> regions. If the page is valid use the nid from pfn_to_nid, otherwise use
> the previous nid.
> 
> Also this pagech changed log to include total sections and a section
> size.
> 
> i.e.
> allocated 100663296 bytes of page_ext for 64 sections (1 section : 0x8000000)

Cc Joonsoo, who wrote this code.
Cc Mike, for memblock.

Thanks.

> 
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 2e66d934d63f..506d58b36a1d 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -381,41 +381,43 @@ static int __meminit page_ext_callback(struct notifier_block *self,
>  void __init page_ext_init(void)
>  {
>  	unsigned long pfn;
> -	int nid;
> +	int nid = 0;
> +	struct memblock_region *rgn;
> +	int nr_section = 0;
> +	unsigned long next_section_pfn = 0;
>  
>  	if (!invoke_need_callbacks())
>  		return;
>  
> -	for_each_node_state(nid, N_MEMORY) {
> +	/*
> +	 * iterate each memblock memory region and do not skip a section having
> +	 * !pfn_valid(pfn)
> +	 */
> +	for_each_mem_region(rgn) {
>  		unsigned long start_pfn, end_pfn;
>  
> -		start_pfn = node_start_pfn(nid);
> -		end_pfn = node_end_pfn(nid);
> -		/*
> -		 * start_pfn and end_pfn may not be aligned to SECTION and the
> -		 * page->flags of out of node pages are not initialized.  So we
> -		 * scan [start_pfn, the biggest section's pfn < end_pfn) here.
> -		 */
> +		start_pfn = (unsigned long)(rgn->base >> PAGE_SHIFT);
> +		end_pfn = start_pfn + (unsigned long)(rgn->size >> PAGE_SHIFT);
> +
> +		if (start_pfn < next_section_pfn)
> +			start_pfn = next_section_pfn;
> +
>  		for (pfn = start_pfn; pfn < end_pfn;
>  			pfn = ALIGN(pfn + 1, PAGES_PER_SECTION)) {
>  
> -			if (!pfn_valid(pfn))
> -				continue;
> -			/*
> -			 * Nodes's pfns can be overlapping.
> -			 * We know some arch can have a nodes layout such as
> -			 * -------------pfn-------------->
> -			 * N0 | N1 | N2 | N0 | N1 | N2|....
> -			 */
> -			if (pfn_to_nid(pfn) != nid)
> -				continue;
> +			if (pfn_valid(pfn))
> +				nid = pfn_to_nid(pfn);
> +			nr_section++;
>  			if (init_section_page_ext(pfn, nid))
>  				goto oom;
>  			cond_resched();
>  		}
> +		next_section_pfn = pfn;
>  	}
> +
>  	hotplug_memory_notifier(page_ext_callback, 0);
> -	pr_info("allocated %ld bytes of page_ext\n", total_usage);
> +	pr_info("allocated %ld bytes of page_ext for %d sections (1 section : 0x%x)\n",
> +		total_usage, nr_section, (1 << SECTION_SIZE_BITS));
>  	invoke_init_callbacks();
>  	return;
>  
> -- 
> 2.17.1
>