Re: [PATCH v7 2/3] kho: fix deferred init of kho scratch

["Michał Cłapiński" <mclapinski@google.com>]

[-- Attachment #1: Type: text/plain, Size: 6381 bytes --]

On Wed, Mar 18, 2026 at 10:33 AM Mike Rapoport <rppt@kernel.org> wrote:

> Hi Michal,
>
> On Tue, Mar 17, 2026 at 03:15:33PM +0100, Michal Clapinski wrote:
> > Currently, if DEFERRED is enabled, kho_release_scratch will initialize
>
> Please spell out CONFIG_DEFERRED_STRUCT_PAGE_INIT
>
> > the struct pages and set migratetype of kho scratch. Unless the whole
> > scratch fit below first_deferred_pfn, some of that will be overwritten
> > either by deferred_init_pages or memmap_init_reserved_pages.
>
> Usually we put brackets after function names to make them more visible.
>
> > To fix it, I modified kho_release_scratch to only set the migratetype
>
> Prefer an imperative mood please, e.g. "To fix it, modify
> kho_release_scratch() ..."
>
> > on already initialized pages. Then, modified init_pageblock_migratetype
> > to set the migratetype to CMA if the page is located inside scratch.
> >
> > Signed-off-by: Michal Clapinski <mclapinski@google.com>
> > ---
> >  include/linux/memblock.h           |  2 --
> >  kernel/liveupdate/kexec_handover.c | 10 ++++++----
> >  mm/memblock.c                      | 22 ----------------------
> >  mm/page_alloc.c                    |  7 +++++++
> >  4 files changed, 13 insertions(+), 28 deletions(-)
> >
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index 6ec5e9ac0699..3e217414e12d 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -614,11 +614,9 @@ static inline void memtest_report_meminfo(struct
> seq_file *m) { }
> >  #ifdef CONFIG_MEMBLOCK_KHO_SCRATCH
> >  void memblock_set_kho_scratch_only(void);
> >  void memblock_clear_kho_scratch_only(void);
> > -void memmap_init_kho_scratch_pages(void);
> >  #else
> >  static inline void memblock_set_kho_scratch_only(void) { }
> >  static inline void memblock_clear_kho_scratch_only(void) { }
> > -static inline void memmap_init_kho_scratch_pages(void) {}
> >  #endif
> >
> >  #endif /* _LINUX_MEMBLOCK_H */
> > diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> > index c9b982372d6e..e511a50fab9c 100644
> > --- a/kernel/liveupdate/kexec_handover.c
> > +++ b/kernel/liveupdate/kexec_handover.c
> > @@ -1477,8 +1477,7 @@ static void __init kho_release_scratch(void)
> >  {
> >       phys_addr_t start, end;
> >       u64 i;
> > -
> > -     memmap_init_kho_scratch_pages();
> > +     int nid;
> >
> >       /*
> >        * Mark scratch mem as CMA before we return it. That way we
> > @@ -1486,10 +1485,13 @@ static void __init kho_release_scratch(void)
> >        * we can reuse it as scratch memory again later.
> >        */
> >       __for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> > -                          MEMBLOCK_KHO_SCRATCH, &start, &end, NULL) {
> > +                          MEMBLOCK_KHO_SCRATCH, &start, &end, &nid) {
> >               ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
> >               ulong end_pfn = pageblock_align(PFN_UP(end));
> >               ulong pfn;
> > +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> > +             end_pfn = min(end_pfn, NODE_DATA(nid)->first_deferred_pfn);
> > +#endif
>
> A helper that returns first_deferred_pfn or ULONG_MAX might be beeter
> looking.
>
> >
> >               for (pfn = start_pfn; pfn < end_pfn; pfn +=
> pageblock_nr_pages)
> >                       init_pageblock_migratetype(pfn_to_page(pfn),
> > @@ -1500,8 +1502,8 @@ static void __init kho_release_scratch(void)
> >  void __init kho_memory_init(void)
> >  {
> >       if (kho_in.scratch_phys) {
> > -             kho_scratch = phys_to_virt(kho_in.scratch_phys);
> >               kho_release_scratch();
> > +             kho_scratch = phys_to_virt(kho_in.scratch_phys);
>
> Why this change is needed?
>

It's not necessary but kho_release_scratch() will
call kho_scratch_overlap(). If kho_scratch is NULL, kho_scratch_overlap()
will return early, making it slightly faster. Alternatively, I skip
invoking kho_scratch_overlap() if migratetype is already MIGRATE_CMA.

>
> >               if (kho_mem_retrieve(kho_get_fdt()))
> >                       kho_in.fdt_phys = 0;
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index b3ddfdec7a80..ae6a5af46bd7 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -959,28 +959,6 @@ __init void memblock_clear_kho_scratch_only(void)
> >  {
> >       kho_scratch_only = false;
> >  }
> > -
> > -__init void memmap_init_kho_scratch_pages(void)
> > -{
> > -     phys_addr_t start, end;
> > -     unsigned long pfn;
> > -     int nid;
> > -     u64 i;
> > -
> > -     if (!IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT))
> > -             return;
> > -
> > -     /*
> > -      * Initialize struct pages for free scratch memory.
> > -      * The struct pages for reserved scratch memory will be set up in
> > -      * reserve_bootmem_region()
> > -      */
> > -     __for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> > -                          MEMBLOCK_KHO_SCRATCH, &start, &end, &nid) {
> > -             for (pfn = PFN_UP(start); pfn < PFN_DOWN(end); pfn++)
> > -                     init_deferred_page(pfn, nid);
> > -     }
> > -}
> >  #endif
> >
> >  /**
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index ee81f5c67c18..5ca078dde61d 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -55,6 +55,7 @@
> >  #include <linux/cacheinfo.h>
> >  #include <linux/pgalloc_tag.h>
> >  #include <linux/mmzone_lock.h>
> > +#include <linux/kexec_handover.h>
> >  #include <asm/div64.h>
> >  #include "internal.h"
> >  #include "shuffle.h"
> > @@ -549,6 +550,12 @@ void __meminit init_pageblock_migratetype(struct
> page *page,
> >                    migratetype < MIGRATE_PCPTYPES))
> >               migratetype = MIGRATE_UNMOVABLE;
> >
> > +     /*
> > +      * Mark KHO scratch as CMA so no unmovable allocations are made
> there.
> > +      */
> > +     if (unlikely(kho_scratch_overlap(page_to_phys(page), PAGE_SIZE)))
> > +             migratetype = MIGRATE_CMA;
> > +
>
> Please pick SJ's fixup for the next respin :)
>
> >       flags = migratetype;
> >
> >  #ifdef CONFIG_MEMORY_ISOLATION
> > --
> > 2.53.0.851.ga537e3e6e9-goog
> >
>
> --
> Sincerely yours,
> Mike.
>

[-- Attachment #2: Type: text/html, Size: 8070 bytes --]