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

[Zi Yan <ziy@nvidia.com>]

On 18 Mar 2026, at 11:18, Michał Cłapiński wrote:

> On Wed, Mar 18, 2026 at 4:10 PM Zi Yan <ziy@nvidia.com> wrote:
>>
>> On 17 Mar 2026, at 10:15, Michal Clapinski wrote:
>>
>>> Currently, if DEFERRED is enabled, kho_release_scratch will initialize
>>> 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.
>>>
>>> To fix it, I modified kho_release_scratch to only set the migratetype
>>> 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(-)
>>>
>>
>> <snip>
>>
>>> 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;
>>> +
>>
>> If this is only for deferred init code, why not put it in deferred_free_pages()?
>> Otherwise, all init_pageblock_migratetype() callers need to pay the penalty
>> of traversing kho_scratch array.
>
> Because reserve_bootmem_region() doesn't call deferred_free_pages().
> So I would also have to modify it.
>
> And the early initialization won't pay the penalty of traversing the
> kho_scratch array, since then kho_scratch is NULL.

How about hugetlb_bootmem_init_migratetype(), init_cma_pageblock(),
init_cma_reserved_pageblock(), __init_page_from_nid(), memmap_init_range(),
__init_zone_device_page()?

1. are they having any PFN range overlapping with kho?
2. is kho_scratch NULL for them?

1 tells us whether putting code in init_pageblock_migratetype() could save
the hassle of changing all above locations.
2 tells us how many callers are affected by traversing kho_scratch.

Thanks.

Best Regards,
Yan, Zi