linux-kernel - Re: [PATCH] kho: add support for deferred struct page init

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Message-ID: <CA+CK2bDGvgcGJijAtSSa2k_FWjnZXm2jRiFd6Z9-XjEQ-Y68DQ@mail.gmail.com>
Date: Tue, 16 Dec 2025 10:05:27 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Evangelos Petrongonas <epetron@...zon.de>, Pratyush Yadav <pratyush@...nel.org>, 
	Alexander Graf <graf@...zon.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jason Miu <jasonmiu@...gle.com>, linux-kernel@...r.kernel.org, 
	kexec@...ts.infradead.org, linux-mm@...ck.org, nh-open-source@...zon.com
Subject: Re: [PATCH] kho: add support for deferred struct page init

> > +static struct page *__init kho_get_preserved_page(phys_addr_t phys,
> > +                                               unsigned int order)
> > +{
> > +     unsigned long pfn = PHYS_PFN(phys);
> > +     int nid = early_pfn_to_nid(pfn);
> > +
> > +     for (int i = 0; i < (1 << order); i++)
> > +             init_deferred_page(pfn + i, nid);
>
> This will skip pages below node->first_deferred_pfn, we need to use
> __init_page_from_nid() here.

Mike, but those struct pages should be initialized early anyway. If
they are not yet initialized we have a problem, as they are going to
be re-initialized later.

>
> > +
> > +     return pfn_to_page(pfn);
> > +}
> > +
> >  static void __init deserialize_bitmap(unsigned int order,
> >                                     struct khoser_mem_bitmap_ptr *elm)
> >  {
> > @@ -449,7 +466,7 @@ static void __init deserialize_bitmap(unsigned int order,
> >               int sz = 1 << (order + PAGE_SHIFT);
> >               phys_addr_t phys =
> >                       elm->phys_start + (bit << (order + PAGE_SHIFT));
> > -             struct page *page = phys_to_page(phys);
> > +             struct page *page = kho_get_preserved_page(phys, order);
>
> I think it's better to initialize deferred struct pages later in
> kho_restore_page. deserialize_bitmap() runs before SMP and it already does

The KHO memory should still be accessible early in boot, right?

> heavy lifting of memblock_reserve()s. Delaying struct page initialization
> until restore makes it at least run in parallel with other initialization
> tasks.
>
> I started to work on this just before plumbers and I have something
> untested here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kho/deferred-page/v0.1
>
> >               union kho_page_info info;
> >
> >               memblock_reserve(phys, sz);
> > --
> > 2.43.0
> >
> >
> >
> >
> > Amazon Web Services Development Center Germany GmbH
> > Tamara-Danz-Str. 13
> > 10243 Berlin
> > Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
> > Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
> > Sitz: Berlin
> > Ust-ID: DE 365 538 597
> >
>
> --
> Sincerely yours,
> Mike.