Re: [RFC PATCH 5/7] x86: Call preallocate_vmalloc_pages() later

["Vishal Moola (Oracle)" <vishal.moola@gmail.com>]

On Wed, Nov 12, 2025 at 10:36:36AM -0800, Vishal Moola (Oracle) wrote:
> On Tue, Nov 11, 2025 at 02:29:44PM +0530, Anshuman Khandual wrote:
> > On 20/10/25 5:46 AM, Matthew Wilcox (Oracle) wrote:
> > > When separately allocating ptdesc from struct page, calling
> > > preallocate_vmalloc_pages() from mem_init() is too early as the slab
> > > allocator hasn't been set up yet.  Move preallocate_vmalloc_pages() to
> > > vmalloc_init() which is called after the slab allocator has been set up.
> > > 
> > > Honestly, this patch is a bit bobbins and I'm sure it'll be reworked
> > > before it goes upstream.
> > > 
> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > > ---
> > >  arch/x86/mm/init_64.c |  4 +---
> > >  include/linux/mm.h    | 33 +++++++++++++++++++++++++++++++--
> > >  mm/vmalloc.c          |  2 ++
> > >  3 files changed, 34 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > > index 0e4270e20fad..5270fc24f6f6 100644
> > > --- a/arch/x86/mm/init_64.c
> > > +++ b/arch/x86/mm/init_64.c
> > > @@ -1322,7 +1322,7 @@ static void __init register_page_bootmem_info(void)
> > >   * Only the level which needs to be synchronized between all page-tables is
> > >   * allocated because the synchronization can be expensive.
> > >   */
> > > -static void __init preallocate_vmalloc_pages(void)
> > > +void __init preallocate_vmalloc_pages(void)
> > >  {
> > >  	unsigned long addr;
> > >  	const char *lvl;
> > > @@ -1390,8 +1390,6 @@ void __init mem_init(void)
> > >  	/* Register memory areas for /proc/kcore */
> > >  	if (get_gate_vma(&init_mm))
> > >  		kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR, PAGE_SIZE, KCORE_USER);
> > > -
> > > -	preallocate_vmalloc_pages();
> > >  }
> > >  
> > >  int kernel_set_to_readonly;
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index edcb7d75542f..e60b181da3df 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -1160,6 +1160,12 @@ static inline int is_vmalloc_or_module_addr(const void *x)
> > >  }
> > >  #endif
> > >  
> > > +#ifdef CONFIG_X86
> > > +void __init preallocate_vmalloc_pages(void);
> > > +#else
> > > +static inline void preallocate_vmalloc_pages(void) { }
> > > +#endif
> > > +
> > >  /*
> > >   * How many times the entire folio is mapped as a single unit (eg by a
> > >   * PMD or PUD entry).  This is probably not what you want, except for
> > > @@ -2939,9 +2945,32 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
> > >  }
> > >  #endif /* CONFIG_MMU */
> > >  
> > > +static inline struct page *ptdesc_page(const struct ptdesc *pt)
> > > +{
> > > +	return pt->pt_page;
> > > +}
> > 
> > pt_page has not been added as an element into ptdesc and hence
> > the build fails upto this patch.
> 
> Which commit are you basing this on? It builds and boots fine for me on
> 6.18-rc5. The commits don't apply to mm-new anymore but that sounds
> different...

Ah nevermind, I see what your saying. This and patch 6 don't compile.

> > > +
> > > +static inline struct ptdesc *page_ptdesc(const struct page *page)
> > > +{
> > > +	memdesc_t memdesc = READ_ONCE(page->memdesc);
> > > +
> > > +	if (memdesc_type(memdesc) != MEMDESC_TYPE_PAGE_TABLE) {
> > > +		printk(KERN_EMERG "memdesc %lx index %lx\n", memdesc.v, page->__folio_index);
> > > +		VM_BUG_ON_PAGE(1, page);
> > > +		return NULL;
> > > +	}
> > > +	return (void *)(memdesc.v - MEMDESC_TYPE_PAGE_TABLE);
> > > +}
> > 
> > Ditto - these elements have not been introduced.