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:

> Christoph Lameter wrote:
> > 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?
>
> No. We will have to track what affects sizeof(spinlock_t) manually.
> Not a fun and error prune.

You can generate a config option depending on the size of the object via
Kbuild. Kbuild will determine the setting before building the kernel as a
whole by runing some small C program.

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