linux-kernel - Re: [PATCH v2] mm/page_ext: init page_ext early if there are no deferred struct pages

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Message-ID: <dffcae23-7389-1bfe-723c-9109bd6a0bda@suse.cz>
Date:   Tue, 24 Jan 2023 11:49:36 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Pasha Tatashin <pasha.tatashin@...een.com>, rppt@...nel.org,
        akpm@...ux-foundation.org, mhocko@...e.com, david@...hat.com,
        quic_charante@...cinc.com, lizhe.67@...edance.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm/page_ext: init page_ext early if there are no
 deferred struct pages

On 1/18/23 16:52, Pasha Tatashin wrote:
> page_ext must be initialized after all struct pages are initialized.
> Therefore, page_ext is initialized after page_alloc_init_late(), and
> can optionally be initialized earlier via early_page_ext kernel
> parameter which as a side effect also disables deferred struct pages.
> 
> Allow to automatically init page_ext early when there are no deferred
> struct pages in order to be able to use page_ext during kernel boot
> and track for example page allocations early.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  include/linux/page_ext.h | 2 ++
>  init/main.c              | 6 +++---
>  mm/page_alloc.c          | 6 +++++-
>  mm/page_ext.c            | 2 +-
>  4 files changed, 11 insertions(+), 5 deletions(-)
> 
> Changelog:
> v2: Fixed build issue with CONFIG_PAGE_EXTENSION=n
> 
> diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> index 67314f648aeb..bc2e39090a1f 100644
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -29,6 +29,8 @@ struct page_ext_operations {
>  	bool need_shared_flags;
>  };
>  
> +extern bool deferred_struct_pages;
> +
>  #ifdef CONFIG_PAGE_EXTENSION
>  
>  /*
> diff --git a/init/main.c b/init/main.c
> index e1c3911d7c70..64cd2ff051c4 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -855,8 +855,8 @@ static void __init mm_init(void)
>  	pgtable_init();
>  	debug_objects_mem_init();
>  	vmalloc_init();
> -	/* Should be run after vmap initialization */
> -	if (early_page_ext_enabled())
> +	/* If no deferred init page_ext now, as vmap is fully initialized */
> +	if (!deferred_struct_pages)
>  		page_ext_init();
>  	/* Should be run before the first non-init thread is created */
>  	init_espfix_bsp();
> @@ -1628,7 +1628,7 @@ static noinline void __init kernel_init_freeable(void)
>  	padata_init();
>  	page_alloc_init_late();
>  	/* Initialize page ext after all struct pages are initialized. */
> -	if (!early_page_ext_enabled())
> +	if (deferred_struct_pages)
>  		page_ext_init();
>  
>  	do_basic_setup();
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 99ebb08dc3f2..717f12e83b85 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -430,6 +430,8 @@ EXPORT_SYMBOL(nr_online_nodes);
>  
>  int page_group_by_mobility_disabled __read_mostly;
>  
> +bool deferred_struct_pages __meminitdata;
> +
>  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>  /*
>   * During boot we initialize deferred pages on-demand, as needed, but once
> @@ -6803,8 +6805,10 @@ void __meminit memmap_init_range(unsigned long size, int nid, unsigned long zone
>  		if (context == MEMINIT_EARLY) {
>  			if (overlap_memmap_init(zone, &pfn))
>  				continue;
> -			if (defer_init(nid, pfn, zone_end_pfn))
> +			if (defer_init(nid, pfn, zone_end_pfn)) {
> +				deferred_struct_pages = true;
>  				break;
> +			}
>  		}
>  
>  		page = pfn_to_page(pfn);
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index e2c22ffdbb81..dc1626be458b 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -92,7 +92,7 @@ unsigned long page_ext_size;
>  static unsigned long total_usage;
>  static struct page_ext *lookup_page_ext(const struct page *page);
>  
> -bool early_page_ext;
> +bool early_page_ext __meminitdata;
>  static int __init setup_early_page_ext(char *str)
>  {
>  	early_page_ext = true;