linux-kernel - Re: [PATCH v2 RESEND] crash: Export PAGE_UNACCEPTED_MAPCOUNT

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Message-ID: <Z+344FNhxiMonoZb@MiWiFi-R3L-srv>
Date: Thu, 3 Apr 2025 10:56:32 +0800
From: Baoquan He <bhe@...hat.com>
To: Zhiquan Li <zhiquan1.li@...el.com>, k-hagio-ab@....com,
	yamazaki-msmt@....com, lijiang@...hat.com, ltao@...hat.com
Cc: akpm@...ux-foundation.org, vgoyal@...hat.com, dyoung@...hat.com,
	kirill.shutemov@...ux.intel.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 RESEND] crash: Export PAGE_UNACCEPTED_MAPCOUNT_VALUE
 to vmcoreinfo

Add makedumpfile/Crash utilities maintainers to let them know.

On 04/03/25 at 11:08am, Zhiquan Li wrote:
> On Intel TDX guest, unaccepted memory is unusable free memory which is
> not managed by buddy, until it's accepted by guest.  Before that, it
> cannot be accessed by the first kernel as well as the kexec'ed kernel.
> The kexec'ed kernel will skip these pages and fill in zero data for the
> reader of vmcore.
> 
> The dump tool like makedumpfile creates a page descriptor (size 24
> bytes) for each non-free page, including zero data page, but it will not
> create descriptor for free pages.  If it is not able to distinguish
> these unaccepted pages with zero data pages, a certain amount of space
> will be wasted in proportion (~1/170).  In fact, as a special kind of
> free page the unaccepted pages should be excluded, like the real free
> pages.
> 
> Export the page type PAGE_UNACCEPTED_MAPCOUNT_VALUE to vmcoreinfo, so
> that dump tool can identify whether a page is unaccepted.
> 
> Link: https://lore.kernel.org/all/20240809114854.3745464-5-kirill.shutemov@linux.intel.com/
> 
> Signed-off-by: Zhiquan Li <zhiquan1.li@...el.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Looks good to me.

Acked-by: Baoquan He <bhe@...hat.com>

> 
> ---
> Vmcore size statistic of a freshly booted TD VM with different memory
> sizes:
> 
>   VM.mem | Before  After
>   -------+----------------
>   512G   | ~4.9G   ~2.0G
>   256G   | ~2.0G   ~1.1G
> 
> Most of changes are done by makedumpfile, but the prerequisite is kernel
> needs to export an indicator to identify unaccepted pages in vmcoreinfo.
> 
> V2 RESEND note:
> - No changes on this, just rebasd to v6.14.
> 
> V1: https://lore.kernel.org/all/20250103074941.3651765-1-zhiquan1.li@intel.com/
> 
> Changes since V1:
> - Rebase to v6.14-rc5.
> - Added document into admin-guide/kdump/vmcoreinfo.rst per Dave's
>   suggestion.
> - Add Kirill's Reviewed-by tag.
> ---
>  Documentation/admin-guide/kdump/vmcoreinfo.rst | 2 +-
>  kernel/vmcore_info.c                           | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> index 0f714fc945ac..3b47916f1856 100644
> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> @@ -331,7 +331,7 @@ PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision|PG_head_mask|P
>  Page attributes. These flags are used to filter various unnecessary for
>  dumping pages.
>  
> -PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
> +PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_unaccepted)
>  -----------------------------------------------------------------------------
>  
>  More page attributes. These flags are used to filter various unnecessary for
> diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
> index 1fec61603ef3..e066d31d08f8 100644
> --- a/kernel/vmcore_info.c
> +++ b/kernel/vmcore_info.c
> @@ -210,6 +210,10 @@ static int __init crash_save_vmcoreinfo_init(void)
>  	VMCOREINFO_NUMBER(PAGE_HUGETLB_MAPCOUNT_VALUE);
>  #define PAGE_OFFLINE_MAPCOUNT_VALUE	(PGTY_offline << 24)
>  	VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
> +#ifdef CONFIG_UNACCEPTED_MEMORY
> +#define PAGE_UNACCEPTED_MAPCOUNT_VALUE	(PGTY_unaccepted << 24)
> +	VMCOREINFO_NUMBER(PAGE_UNACCEPTED_MAPCOUNT_VALUE);
> +#endif
>  
>  #ifdef CONFIG_KALLSYMS
>  	VMCOREINFO_SYMBOL(kallsyms_names);
> 
> base-commit: 38fec10eb60d687e30c8c6b5420d86e8149f7557
> -- 
> 2.25.1
> 
>