linux-kernel - Re: linux-next: Tree for May 13 (mm/page_alloc.c, <linux/mm.h>: sizeof(struct page))

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Date:   Thu, 13 May 2021 22:27:25 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: linux-next: Tree for May 13 (mm/page_alloc.c, <linux/mm.h>:
 sizeof(struct page))

On Thu, May 13, 2021 at 10:29:49AM -0700, Randy Dunlap wrote:
> On 5/12/21 10:44 PM, Stephen Rothwell wrote:
> > Hi all,
> > 
> > Changes since 20210512:
> > 
> 
> on x86_64:
> 
> In function ‘__mm_zero_struct_page.isra.75’,
>     inlined from ‘__init_single_page.isra.76’ at ../mm/page_alloc.c:1494:2:
> ./../include/linux/compiler_types.h:328:38: error: call to ‘__compiletime_assert_162’ declared with attribute error: BUILD_BUG_ON failed: sizeof(struct page) > 80

Hmm.

                struct {
                        long unsigned int _pt_pad_1;     /*     8     8 */
                        pgtable_t  pmd_huge_pte;         /*    16     8 */
                        long unsigned int _pt_pad_2;     /*    24     8 */
                        union {
                                struct mm_struct * pt_mm; /*    32     8 */
                                atomic_t pt_frag_refcount; /*    32     4 */
                        };                               /*    32     8 */
                        spinlock_t ptl;                  /*    40    72 */
                };                                       /*     8   104 */

#if ALLOC_SPLIT_PTLOCKS
                        spinlock_t *ptl;
#else
                        spinlock_t ptl;
#endif

something has disabled ALLOC_SPLIT_PTLOCKS when it ought to be enabled.

#if USE_SPLIT_PTE_PTLOCKS
#define ALLOC_SPLIT_PTLOCKS     (SPINLOCK_SIZE > BITS_PER_LONG/8)
#else
#define ALLOC_SPLIT_PTLOCKS     0
#endif

Oh.  This is Anshuman's fault.

commit 9b8a39056e2472592a5e5897987387f43038b8ba
Author: Anshuman Khandual <anshuman.khandual@....com>
Date:   Tue May 11 15:06:01 2021 +1000

    mm/thp: make ALLOC_SPLIT_PTLOCKS dependent on USE_SPLIT_PTE_PTLOCKS