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SubjectRe: [PATCH V2] mm/thp: Make ALLOC_SPLIT_PTLOCKS dependent on USE_SPLIT_PTE_PTLOCKS
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On 5/20/21 4:47 PM, Matthew Wilcox wrote:
> On Wed, May 19, 2021 at 01:03:06PM +0530, Anshuman Khandual wrote:
>> Split ptlocks need not be defined and allocated unless they are being used.
>> ALLOC_SPLIT_PTLOCKS is inherently dependent on USE_SPLIT_PTE_PTLOCKS. This
>> just makes it explicit and clear. While here drop the spinlock_t element
>> from the struct page when USE_SPLIT_PTE_PTLOCKS is not enabled.
>
> I didn't spot this email yesterday. I'm not a fan. Isn't struct page
> already complicated enough without adding another ifdef to it? Surely
> there's a better way than this.

This discussion thread just got dropped off the radar, sorry about it.
None of the spinlock_t elements are required unless split ptlocks are
in use. I understand your concern regarding yet another #ifdef in the
struct page definition. But this change is simple and minimal. Do you
have any other particular alternative in mind which I could explore ?

>
>> +++ b/include/linux/mm_types.h
>> @@ -152,10 +152,12 @@ 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 */

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