Re: [PATCH v2 10/13] mm/sparse: remove SECTION_MARKED_PRESENT

[Baoquan He]

On 09/28/26 at 09:28am, David Hildenbrand (Arm) wrote:
> On 9/27/26 21:20, David Carlier wrote:
> > On Mon, Sep 21, 2026 at 09:59:02PM +0200, David Hildenbrand (Arm) wrote:
> >>  enum {
> >> -	SECTION_MARKED_PRESENT_BIT,
> >>  	SECTION_HAS_MEM_MAP_BIT,
> >>  	SECTION_IS_ONLINE_BIT,
> >>  	SECTION_IS_EARLY_BIT,
> > 
> > Hi David,
> 
> Hi!
> 
> > 
> > It seems dropping SECTION_MARKED_PRESENT_BIT shifts the other section flags down
> > one bit. crash hardcodes SECTION_HAS_MEM_MAP as (1UL << 1) in
> > pfn_to_map(), so it now tests SECTION_IS_ONLINE: offline and
> > ZONE_DEVICE sections no longer resolve to a struct page. makedumpfile
> > only checks bit 0 and is fine.
> 
> Thanks. To be expected when relying on kernel internals.
> 
> Which makes me wonder why makedumpfile
> (https://github.com/makedumpfile/makedumpfile) not require any such information.

Makedumpfile requires it too, while it doesn't ask for HAS_MEM_MAP. So
checking MARKED_PRESENT becomes checking HAS_MEM_MAP's value, it luckily
works.

# git grep MARKED_PRESENT
makedumpfile.c:                 if (!(map_mask & SECTION_MARKED_PRESENT)) {
makedumpfile.h:#define SECTION_MARKED_PRESENT  (1UL<<0)


Add makedumpfile maintainer Kazu here.

And add Dave Young here since I heard he is taking over Crash maintenance
as a volunteer.

> 
> > 
> > Keep bit 0 reserved, or export the bits via vmcoreinfo?
> We could export it, or crash can simply detect the change based on the kernel
> version. I remember the latter was done in makedumpfile in the past (although we
> export it).
> 
> I can send a separate patch to export it.
> 
> -- 
> Cheers,
> 
> David