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

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 11, 2025 at 02:29:44PM +0530, Anshuman Khandual wrote:
> pt_page has not been added as an element into ptdesc and hence
> the build fails upto this patch.

Right, sorry, looks like the commit went astray.  Those lines should
have been in a lter patch, and this patch should have been as below.

Adding Joerg to the cc to see if this invocation of
preallocate_vmalloc_pages() is early enough.  Also I'd like feedback on
whether we want to expose preallocate_vmalloc_pages() like this or if we
want something more bland as a name like arch_vmalloc_init().

commit b34c228df965
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
Date:   Sun Oct 19 18:34:36 2025 -0400

    x86: Call preallocate_vmalloc_pages() later
    
    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>

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 3d9a5e4ccaa4..0006b2880bc0 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 3111344b8d05..00ea79340c0c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1177,6 +1177,12 @@ 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
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0832f944544c..8af051136211 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -5385,6 +5385,8 @@ void __init vmalloc_init(void)
 	struct vm_struct *tmp;
 	int i;
 
+	preallocate_vmalloc_pages();
+
 	/*
 	 * Create the cache for vmap_area objects.
 	 */