Re: [PATCH 34/34] mm: dynamically allocate page->ptl if it cannotbe embedded to struct page

[Christoph Lameter]

On Thu, 10 Oct 2013, Kirill A. Shutemov wrote:

> +static inline bool ptlock_alloc(struct page *page)
> +{
> +	if (sizeof(spinlock_t) > sizeof(page->ptl))
> +		return __ptlock_alloc(page);
> +	return true;
> +}

Could you make the check a CONFIG option? CONFIG_PTLOCK_DOES_NOT_FIT_IN_PAGE_STRUCT or
so?

> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -147,7 +147,10 @@ struct page {
>  						 * system if PG_buddy is set.
>  						 */
>  #if USE_SPLIT_PTE_PTLOCKS
> -		spinlock_t ptl;
> +		unsigned long ptl; /* It's spinlock_t if it fits to long,
> +				    * otherwise it's pointer to dynamicaly
> +				    * allocated spinlock_t.
> +				    */

If you had such a CONFIG option then you could use the proper type here.

#ifdef CONFIG_PTLOCK_NOT_FITTING
	spinlock_t *ptl;
#else
	spinlock_t ptl;
#endif

Or some such thing?
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