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From:   lizhe.67@bytedance.com
To:     vbabka@suse.cz
Cc:     Jason@zx2c4.com, akpm@linux-foundation.org, corbet@lwn.net,
        keescook@chromium.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        lizefan.x@bytedance.com, lizhe.67@bytedance.com,
        mark-pk.tsai@mediatek.com, mhiramat@kernel.org, mhocko@suse.com,
        rostedt@goodmis.org, yuanzhu@bytedance.com
Subject: Re: [PATCH v3] page_ext: introduce boot parameter 'early_page_ext'
Date:   Thu, 25 Aug 2022 18:17:50 +0800
Message-Id: <20220825101750.303-1-lizhe.67@bytedance.com>
In-Reply-To: <4a6385a9-8432-21dc-a070-66236c78457b@suse.cz>
References: <4a6385a9-8432-21dc-a070-66236c78457b@suse.cz>
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On 25 Aug 2022 11:36:31 +0200, vbabka@suse.cz wrote:
>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?

There is no problem with or without the parameter now.

>
>> 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?

Yes you are right. I will fix it in my v4 patch. Thanks!

>
>> +
>>  #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;