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

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Message-ID: <d3h7ptoh63zleuhcfrtnj4jagggk7omlylyqys3vhrd3uw2bk3@d54obusanwdk>
Date: Fri, 3 Jan 2025 16:26:40 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Zhiquan Li <zhiquan1.li@...el.com>
Cc: bhe@...hat.com, vgoyal@...hat.com, dyoung@...hat.com, 
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crash: Export PAGE_UNACCEPTED_MAPCOUNT_VALUE to
 vmcoreinfo

On Fri, Jan 03, 2025 at 03:49:41PM +0800, 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.  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.
> 
> Signed-off-by: Zhiquan Li <zhiquan1.li@...el.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov