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Date:   Thu, 25 Aug 2022 11:36:31 +0200
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Subject: Re: [PATCH v3] page_ext: introduce boot parameter 'early_page_ext'
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To:     lizhe.67@bytedance.com, akpm@linux-foundation.org, mhocko@suse.com,
        mhiramat@kernel.org, keescook@chromium.org, Jason@zx2c4.com,
        mark-pk.tsai@mediatek.com, rostedt@goodmis.org, corbet@lwn.net
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, lizefan.x@bytedance.com, yuanzhu@bytedance.com
References: <20220825063102.92307-1-lizhe.67@bytedance.com>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20220825063102.92307-1-lizhe.67@bytedance.com>
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On 8/25/22 08:31, lizhe.67@bytedance.com wrote:
> From: Li Zhe <lizhe.67@bytedance.com>
> 
> In 'commit 2f1ee0913ce5 ("Revert "mm: use early_pfn_to_nid in page_ext_init"")',
> we call page_ext_init() after page_alloc_init_late() to avoid some panic
> problem. It seems that we cannot track early page allocations in current
> kernel even if page structure has been initialized early.
> 
> This patch introduce a new boot parameter 'early_page_ext' to resolve this
> problem. If we pass it to kernel, function page_ext_init() will be moved
> up and feature 'deferred initialization of struct pages' will be disabled.
> It can help us to catch early page allocations. This is useful especially
> when we find that the free memory value is not the same right after
> different kernel booting.
> 
> Changelogs:
> 
> v1->v2:
> - use a cmd line parameter to move up function page_ext_init() instead of
>   using CONFIG_DEFERRED_STRUCT_PAGE_INIT
> - fix oom problem[1]
> 
> v2->v3:
> - make adjustments suggested by Michal Hocko
> 
> v1 patch: https://lore.kernel.org/lkml/Yv3r6Y1vh+6AbY4+@dhcp22.suse.cz/T/

IIRC v1 failed to boot in some automatic bot test. Will this not fail with
the same config/hw combination when the parameter is passed?

> v2 patch: https://lore.kernel.org/lkml/20220824065058.81051-1-lizhe.67@bytedance.com/T/
> 
> [1]: https://lore.kernel.org/linux-mm/YwHmXLu5txij+p35@xsang-OptiPlex-9020/
> 
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
>  include/linux/page_ext.h                        | 11 +++++++++++
>  init/main.c                                     |  6 +++++-
>  mm/page_alloc.c                                 |  2 ++
>  mm/page_ext.c                                   | 12 ++++++++++++
>  5 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index d7f30902fda0..7b5726828ac0 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1471,6 +1471,12 @@
>  			Permit 'security.evm' to be updated regardless of
>  			current integrity status.
>  
> +	early_page_ext [KNL] Boot-time early page_ext initializing option.
> +			This boot parameter disables the deferred initialization
> +			of struct page and move up function page_ext_init() in
> +			order to catch early page allocations. Available with
> +			CONFIG_PAGE_EXTENSION=y.
> +
>  	failslab=
>  	fail_usercopy=
>  	fail_page_alloc=
> diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> index fabb2e1e087f..68d690649234 100644
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -36,9 +36,15 @@ struct page_ext {
>  	unsigned long flags;
>  };
>  
> +extern bool early_page_ext;
>  extern unsigned long page_ext_size;
>  extern void pgdat_page_ext_init(struct pglist_data *pgdat);
>  
> +static inline bool early_page_ext_enable(void)
> +{
> +	return early_page_ext;
> +}

I think it should better be named early_page_ext_enabled() as it returns the
status, not sets it to true?

> +
>  #ifdef CONFIG_SPARSEMEM
>  static inline void page_ext_init_flatmem(void)
>  {
> @@ -67,6 +73,11 @@ static inline struct page_ext *page_ext_next(struct page_ext *curr)
>  #else /* !CONFIG_PAGE_EXTENSION */
>  struct page_ext;
>  
> +static inline bool early_page_ext_enable(void)
> +{
> +	return false;
> +}
> +
>  static inline void pgdat_page_ext_init(struct pglist_data *pgdat)
>  {
>  }
> diff --git a/init/main.c b/init/main.c
> index 91642a4e69be..d95edb67a499 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -849,6 +849,9 @@ static void __init mm_init(void)
>  	pgtable_init();
>  	debug_objects_mem_init();
>  	vmalloc_init();
> +	/* Should be run after vmap initialization */
> +	if (early_page_ext_enable())
> +		page_ext_init();
>  	/* Should be run before the first non-init thread is created */
>  	init_espfix_bsp();
>  	/* Should be run after espfix64 is set up. */
> @@ -1606,7 +1609,8 @@ static noinline void __init kernel_init_freeable(void)
>  	padata_init();
>  	page_alloc_init_late();
>  	/* Initialize page ext after all struct pages are initialized. */
> -	page_ext_init();
> +	if (!early_page_ext_enable())
> +		page_ext_init();
>  
>  	do_basic_setup();
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e5486d47406e..e580b197aa1e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -482,6 +482,8 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>  {
>  	static unsigned long prev_end_pfn, nr_initialised;
>  
> +	if (early_page_ext_enable())
> +		return false;
>  	/*
>  	 * prev_end_pfn static that contains the end of previous zone
>  	 * No need to protect because called very early in boot before smp_init.
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 3dc715d7ac29..bf4f2a12d7dc 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -85,6 +85,18 @@ unsigned long page_ext_size = sizeof(struct page_ext);
>  
>  static unsigned long total_usage;
>  
> +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> +bool early_page_ext __meminitdata;
> +#else
> +bool early_page_ext __meminitdata = true;
> +#endif
> +static int __init setup_early_page_ext(char *str)
> +{
> +	early_page_ext = true;
> +	return 0;
> +}
> +early_param("early_page_ext", setup_early_page_ext);
> +
>  static bool __init invoke_need_callbacks(void)
>  {
>  	int i;