Re: [PATCH v6 4/9] mm: thp: Introduce anon_orders and anon_always_mask sysfs files

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 29 Sep 2023 12:44:15 +0100 Ryan Roberts <ryan.roberts@arm.com> wrote:

> In preparation for adding support for anonymous large folios that are
> smaller than the PMD-size, introduce 2 new sysfs files that will be used
> to control the new behaviours via the transparent_hugepage interface.
> For now, the kernel still only supports PMD-order anonymous THP, so when
> reading back anon_orders, it will reflect that. Therefore there are no
> behavioural changes intended here.

powerpc strikes again.  ARCH=powerpc allmodconfig:


In file included from ./include/linux/bits.h:6,
                 from ./include/linux/ratelimit_types.h:5,
                 from ./include/linux/printk.h:9,
                 from ./include/asm-generic/bug.h:22,
                 from ./arch/powerpc/include/asm/bug.h:116,
                 from ./include/linux/bug.h:5,
                 from ./include/linux/mmdebug.h:5,
                 from ./include/linux/mm.h:6,
                 from mm/huge_memory.c:8:
./include/vdso/bits.h:7:33: error: initializer element is not constant
    7 | #define BIT(nr)                 (UL(1) << (nr))
      |                                 ^
mm/huge_memory.c:77:47: note: in expansion of macro 'BIT'
   77 | unsigned int huge_anon_orders __read_mostly = BIT(PMD_ORDER);
      |                                               ^~~

We keep tripping over this.  I wish there was a way to fix it.



Style whine: an all-caps identifier is supposed to be a constant,
dammit.

	#define PTE_INDEX_SIZE  __pte_index_size

Nope.



I did this:

--- a/mm/huge_memory.c~mm-thp-introduce-anon_orders-and-anon_always_mask-sysfs-files-fix
+++ a/mm/huge_memory.c
@@ -74,7 +74,7 @@ static unsigned long deferred_split_scan
 static atomic_t huge_zero_refcount;
 struct page *huge_zero_page __read_mostly;
 unsigned long huge_zero_pfn __read_mostly = ~0UL;
-unsigned int huge_anon_orders __read_mostly = BIT(PMD_ORDER);
+unsigned int huge_anon_orders __read_mostly;
 static unsigned int huge_anon_always_mask __read_mostly;
 
 /**
@@ -528,6 +528,9 @@ static int __init hugepage_init_sysfs(st
 {
 	int err;
 
+	/* powerpc's PMD_ORDER isn't a compile-time constant */
+	huge_anon_orders = BIT(PMD_ORDER);
+
 	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 	if (unlikely(!*hugepage_kobj)) {
 		pr_err("failed to create transparent hugepage kobject\n");
_


I assume this is set up early enough.

I don't know why powerpc's PTE_INDEX_SIZE is variable.  Hopefully it
has been set up by this time and it won't get altered.