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To:     Zhenhua Huang <zhenhuah@codeaurora.org>, akpm@linux-foundation.org
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <1602839640-13125-1-git-send-email-zhenhuah@codeaurora.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] mm: fix page_owner initializing issue for arm32
Message-ID: <1a1a80b8-2ce4-9346-f333-68f3bb8b25c0@suse.cz>
Date:   Fri, 16 Oct 2020 12:41:04 +0200
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On 10/16/20 11:14 AM, Zhenhua Huang wrote:
> Page owner of pages used by page owner itself used is missing on arm32 targets.
> The reason is dummy_handle and failure_handle is not initialized correctly.
> Buddy allocator is used to initialize these two handles. However, buddy
> allocator is not ready when page owner calls it. This change fixed that by
> initializing page owner after buddy initialization.
> 
> The working flow before and after this change are:
> original logic:
> 1. allocated memory for page_ext(using memblock).
> 2. invoke the init callback of page_ext_ops like
> page_owner(using buddy allocator).
> 3. initialize buddy.
> 
> after this change:
> 1. allocated memory for page_ext(using memblock).
> 2. initialize buddy.
> 3. invoke the init callback of page_ext_ops like
> page_owner(using buddy allocator).
> 
> with the change, failure/dummy_handle can get its correct value and
> page owner output for example has the one for page owner itself:
> Page allocated via order 2, mask 0x6202c0(GFP_USER|__GFP_NOWARN), pid 1006, ts
> 67278156558 ns
> PFN 543776 type Unmovable Block 531 type Unmovable Flags 0x0()
>   init_page_owner+0x28/0x2f8
>   invoke_init_callbacks_flatmem+0x24/0x34
>   start_kernel+0x33c/0x5d8
>     (null)

register_dummy_stack should also appear in the above. Either one too many is 
skipped in arm32 stack saving, or the noinline is not honoured. Could be 
investigated separately.

> 
> Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>

This should be safe, as the sparse variant page_ext_init() runs even later, so:

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

Nit below:

> ---
>   include/linux/page_ext.h | 8 ++++++++
>   init/main.c              | 2 ++
>   mm/page_ext.c            | 8 +++++++-
>   3 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> index cfce186..aff81ba 100644
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -44,8 +44,12 @@ static inline void page_ext_init_flatmem(void)
>   {
>   }
>   extern void page_ext_init(void);
> +static inline void page_ext_init_flatmem_late(void)
> +{
> +}
>   #else
>   extern void page_ext_init_flatmem(void);
> +extern void page_ext_init_flatmem_late(void);
>   static inline void page_ext_init(void)
>   {
>   }
> @@ -76,6 +80,10 @@ static inline void page_ext_init(void)
>   {
>   }
>   
> +static inline void page_ext_init_flatmem_late(void)
> +{
> +}
> +
>   static inline void page_ext_init_flatmem(void)
>   {
>   }
> diff --git a/init/main.c b/init/main.c
> index 130376e..b34c475 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -818,6 +818,8 @@ static void __init mm_init(void)
>   	init_debug_pagealloc();
>   	report_meminit();
>   	mem_init();
> +	/* page_owner must be initialized after buddy is ready */
> +	page_ext_init_flatmem_late();
>   	kmem_cache_init();
>   	kmemleak_init();
>   	pgtable_init();
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index a3616f7..373f7a1 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -99,6 +99,13 @@ static void __init invoke_init_callbacks(void)
>   	}
>   }
>   
> +#if !defined(CONFIG_SPARSEMEM)

#ifndef is more common if you don't need boolean ops on multiple configs

> +void __init page_ext_init_flatmem_late(void)
> +{
> +	invoke_init_callbacks();
> +}
> +#endif
> +
>   static inline struct page_ext *get_entry(void *base, unsigned long index)
>   {
>   	return base + page_ext_size * index;
> @@ -177,7 +184,6 @@ void __init page_ext_init_flatmem(void)
>   			goto fail;
>   	}
>   	pr_info("allocated %ld bytes of page_ext\n", total_usage);
> -	invoke_init_callbacks();
>   	return;
>   
>   fail:
>