On 5/14/21 2:57 AM, Matthew Wilcox wrote:
> 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@xxxxxxx>
> Date: Tue May 11 15:06:01 2021 +1000
>
> mm/thp: make ALLOC_SPLIT_PTLOCKS dependent on USE_SPLIT_PTE_PTLOCKS
>
>
Previously ALLOC_SPLIT_PTLOCKS was evaluated and the spin lock element
in struct page was getting created independent of whether split pte
locks are being used or not. AFAICS without USE_SPLIT_PTE_PTLOCKS, it
does not really matter whether struct page has spinlock_t *ptl or ptl
element because that is not going to be used. Should the BUILD_BUG_ON()
evaluation be changed when USE_SPLIT_PTE_PTLOCKS is not enabled or we
could something like this which drops the ptl element in such cases ?
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -152,11 +152,13 @@ struct page {
struct mm_struct *pt_mm; /* x86 pgds only */
atomic_t pt_frag_refcount; /* powerpc */
};
+#if USE_SPLIT_PTE_PTLOCKS
#if ALLOC_SPLIT_PTLOCKS
spinlock_t *ptl;
#else
spinlock_t ptl;
#endif
+#endif
};
struct { /* ZONE_DEVICE pages */
/** @pgmap: Points to the hosting device page map. */
