Re: [PATCH v6 06/10] memblock: introduce MEMBLOCK_NODUMP flag

[Mike Rapoport]

On Fri, Sep 18, 2026 at 04:08:10PM +0800, Baoquan He wrote:
> On 09/02/26 at 03:31pm, Wandun Chen wrote:
> > From: Wandun Chen <chenwandun@xxxxxxxxxxx>
> > 
> > Add MEMBLOCK_NODUMP to mark regions that should be excluded from
> > kdump vmcores.
> > 
> > The flag is meant for reserved memory that carries no data useful for
> > crash analysis. Reusable reserved regions such as CMA may hold useful
> > data, so these regions must not be marked MEMBLOCK_NODUMP. Subsequent
> > patches wire this up for /reserved-memory and /memreserve/ entries.
> > 
> > Suggested-by: Rob Herring <robh@xxxxxxxxxx>
> > Signed-off-by: Wandun Chen <chenwandun@xxxxxxxxxxx>
> > Tested-by: Meijing Zhao <zhaomeijing@xxxxxxxxxxx>
> > ---
> >  include/linux/memblock.h |  9 +++++++++
> >  mm/memblock.c            | 16 ++++++++++++++++
> >  2 files changed, 25 insertions(+)
> > 
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index d62db9e776cf..b2fcf11fba2b 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -52,6 +52,8 @@ extern unsigned long long max_possible_pfn;
> >   * kernel that we know is good to use. It is the only memory that
> >   * allocations may happen from in this phase.
> >   * @MEMBLOCK_RSRV_HUGETLB: memory is reserved for hugetlb pages
> > + * @MEMBLOCK_NODUMP: exclude from kdump vmcore. It carries no data useful
> > + * for crash analysis (e.g. firmware carveouts).
> >   */
> >  enum memblock_flags {
> >  	MEMBLOCK_NONE		= 0x0,	/* No special request */
> > @@ -63,6 +65,7 @@ enum memblock_flags {
> >  	MEMBLOCK_RSRV_KERN	= 0x20,	/* memory reserved for kernel use */
> >  	MEMBLOCK_KHO_SCRATCH	= 0x40,	/* scratch memory for kexec handover */
> >  	MEMBLOCK_RSRV_HUGETLB	= 0x80, /* memory reserved for hugetlb pages */
> > +	MEMBLOCK_NODUMP		= 0x100,/* exclude from kdump vmcore */
> >  };
> >  
> >  /**
> > @@ -160,6 +163,7 @@ int memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size);
> >  int memblock_reserved_mark_kern(phys_addr_t base, phys_addr_t size);
> >  int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size);
> >  int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size);
> > +int memblock_mark_nodump(phys_addr_t base, phys_addr_t size);
> >  
> >  void memblock_free(void *ptr, size_t size);
> >  void reset_all_zones_managed_pages(void);
> > @@ -306,6 +310,11 @@ static inline bool memblock_is_kho_scratch(struct memblock_region *m)
> >  	return m->flags & MEMBLOCK_KHO_SCRATCH;
> >  }
> >  
> > +static inline bool memblock_is_nodump(struct memblock_region *m)
> > +{
> > +	return m->flags & MEMBLOCK_NODUMP;
> > +}
> > +
> >  int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
> >  			    unsigned long  *end_pfn);
> >  void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index f2952d725c10..2e87f39826dd 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -1204,6 +1204,21 @@ __init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
> >  				    MEMBLOCK_KHO_SCRATCH);
> >  }
> >  
> > +/**
> > + * memblock_mark_nodump - Mark a memory region with flag MEMBLOCK_NODUMP.
> > + * @base: the base phys addr of the region
> > + * @size: the size of the region
> > + *
> > + * Mark the region as not to be included in crash dumps.
> > + *
> > + * Return: 0 on success, -errno on failure.
> > + */
> > +int __init_memblock memblock_mark_nodump(phys_addr_t base, phys_addr_t size)
>       ~~~~~~~~~~~~~~^
> Is it impossible to use at runtime even thought it claims to be generic?

This should only happen at boot.

Allowing modifications of memblock properties in runtime is a can of worms
I don't want to open.
 
> > +{
> > +	return memblock_setclr_flag(&memblock.memory, base, size, 1,
> > +				    MEMBLOCK_NODUMP);
> > +}
> > +
> >  static bool should_skip_region(struct memblock_type *type,
> >  			       struct memblock_region *m,
> >  			       int nid, int flags)
> > @@ -2887,6 +2902,7 @@ static const char * const flagname[] = {
> >  	[ilog2(MEMBLOCK_RSRV_KERN)] = "RSV_KERN",
> >  	[ilog2(MEMBLOCK_KHO_SCRATCH)] = "KHO_SCRATCH",
> >  	[ilog2(MEMBLOCK_RSRV_HUGETLB)] = "RSV_HUGETLB",
> > +	[ilog2(MEMBLOCK_NODUMP)] = "NODUMP",
> >  };
> >  
> >  static int memblock_debug_show(struct seq_file *m, void *private)
> > -- 
> > 2.43.0
> > 

-- 
Sincerely yours,
Mike.