linux-kernel - Re: [PATCH v4 20/36] mm/page_ext: enable early_page_ext when CONFIG_MEM_ALLOC_PROFILING

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Message-ID: <49c33680-2a08-4d59-86ba-72f8850099a5@suse.cz>
Date: Tue, 27 Feb 2024 11:18:02 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v4 20/36] mm/page_ext: enable early_page_ext when
 CONFIG_MEM_ALLOC_PROFILING_DEBUG=y

On 2/21/24 20:40, Suren Baghdasaryan wrote:
> For all page allocations to be tagged, page_ext has to be initialized
> before the first page allocation. Early tasks allocate their stacks
> using page allocator before alloc_node_page_ext() initializes page_ext
> area, unless early_page_ext is enabled. Therefore these allocations will
> generate a warning when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled.
> Enable early_page_ext whenever CONFIG_MEM_ALLOC_PROFILING_DEBUG=y to
> ensure page_ext initialization prior to any page allocation. This will
> have all the negative effects associated with early_page_ext, such as
> possible longer boot time, therefore we enable it only when debugging
> with CONFIG_MEM_ALLOC_PROFILING_DEBUG enabled and not universally for
> CONFIG_MEM_ALLOC_PROFILING.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

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

> ---
>  mm/page_ext.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 3c58fe8a24df..e7d8f1a5589e 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -95,7 +95,16 @@ unsigned long page_ext_size;
>  
>  static unsigned long total_usage;
>  
> +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> +/*
> + * To ensure correct allocation tagging for pages, page_ext should be available
> + * before the first page allocation. Otherwise early task stacks will be
> + * allocated before page_ext initialization and missing tags will be flagged.
> + */
> +bool early_page_ext __meminitdata = true;
> +#else
>  bool early_page_ext __meminitdata;
> +#endif
>  static int __init setup_early_page_ext(char *str)
>  {
>  	early_page_ext = true;