Re: [PATCH] mm: ignore nomap memory during mirror init

[Mike Rapoport <rppt@kernel.org>]

On Fri, Jul 18, 2025 at 09:37:48AM +0800, mawupeng wrote:
> 
> 
> On 2025/7/17 21:37, Mike Rapoport wrote:
> > On Thu, Jul 17, 2025 at 07:06:52PM +0800, mawupeng wrote:
> >>
> >> On 2025/7/17 18:29, Mike Rapoport wrote:
> >>> On Thu, Jul 17, 2025 at 04:57:23PM +0800, Wupeng Ma wrote:
> >>>> When memory mirroring is enabled, the BIOS may reserve memory regions
> >>>> at the start of the physical address space without the MR flag. This will
> >>>> lead to zone_movable_pfn to be updated to the start of these reserved
> >>>> regions, resulting in subsequent mirrored memory being ignored.
> >>>>
> >>>> Here is the log with efi=debug enabled:
> >>>>   efi:   0x084004000000-0x0842bf37ffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x0842bf380000-0x0842c21effff [Loader Code |   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x0842c21f0000-0x0847ffffffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
> >>>>   efi:   0x085000000000-0x085fffffffff [Conventional|   |  |  |...|WB|WT|WC|  ]
> >>>> ...
> >>>>   efi:   0x084000000000-0x084003ffffff [Reserved    |   |  |  |...|WB|WT|WC|  ]
> >>>>
> >>>> Since this kind of memory can not be used by kernel. ignore nomap memory to fix
> >>>> this issue.
> >>
> >> Since the first non-mirror pfn of this node is 0x084000000000, then zone_movable_pfn 
> >> for this node will be updated to this. This will lead to Mirror Region 
> >>   - 0x084004000000-0x0842bf37ffff
> >>   - 0x0842bf380000-0x0842c21effff 
> >>   - 0x0842c21f0000-0x0847ffffffff
> >> be seen as non-mirror memory since zone_movable_pfn will be the start_pfn of this node
> >> in adjust_zone_range_for_zone_movable().
> > 
> > What do you mean by "seen as non-mirror memory"?
> 
> It mean these memory range will be add to movable zone.
> 
> > 
> > What is the problem with having movable zone on that node start at
> > 0x084000000000?
> > 
> > Can you post the kernel log up to "Memory: nK/mK available" line for more
> > context?
> 
> Memory: nK/mK available can not see be problem here, since there is nothing wrong
> with the total memory. However this problem can be shown via lsmem --output-all

I didn't ask for that particular line but for *up to that line*.
 
> w/o this patch
> [root@localhost ~]# lsmem --output-all
> RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
> 0x0000084000000000-0x00000847ffffffff   32G online       yes   67584-67839    0 Movable
> 0x0000085000000000-0x0000085fffffffff   64G online       yes   68096-68607    0 Movable
> 
> w/ this patch
> [root@localhost ~]# lsmem --output-all
> RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
> 0x0000084000000000-0x00000847ffffffff   32G online       yes   8448-8479    0  Normal
> 0x0000085000000000-0x0000085fffffffff   64G online       yes   8512-8575    0 Movable

As I see the problem, you have a problematic firmware that fails to report
memory as mirrored because it reserved for firmware own use. This causes
for non-mirrored memory to appear before mirrored memory. And this breaks
an assumption in find_zone_movable_pfns_for_nodes() that mirrored memory
always has lower addresses than non-mirrored memory and you end up wiht
having all the memory in movable zone.

So to workaround this firmware issue you propose a hack that would skip
NOMAP regions while calculating zone_movable_pfn because your particular
firmware reports the reserved mirrored memory as NOMAP.

Why don't you simply pass "kernelcore=32G" on the command line and you'll
get the same result.

> As shown above, All memory in this node is added to Zone Movable even some range of the memory
> is mirror memory. With this patch, 0x0000084000000000-0x00000847ffffffff will be added to
> zone normal as expected since the MR attribute.

-- 
Sincerely yours,
Mike.