Re: [PATCH 8/9] mm: implement split page table lock for PMD level

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Peter Zijlstra wrote:
> On Fri, Sep 13, 2013 at 04:06:15PM +0300, Kirill A. Shutemov wrote:
> > +#if USE_SPLIT_PMD_PTLOCKS
> > +
> > +static inline void pgtable_pmd_page_ctor(struct page *page)
> > +{
> > +	spin_lock_init(&page->ptl);
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +	page->pmd_huge_pte = NULL;
> > +#endif
> > +}
> > +
> > +static inline void pgtable_pmd_page_dtor(struct page *page)
> > +{
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +	VM_BUG_ON(page->pmd_huge_pte);
> > +#endif
> > +}
> > +
> > +#define pmd_huge_pte(mm, pmd) (virt_to_page(pmd)->pmd_huge_pte)
> > +
> > +#else
> 
> So on -rt we have the problem that spinlock_t is rather huge (its a
> rtmutex) so instead of blowing up the pageframe like that we treat
> page->pte as a pointer and allocate the spinlock.
> 
> Since allocations could fail the above ctor path gets 'interesting'.
> 
> It would be good if new code could assume the ctor could fail so we
> don't have to replicate that horror-show.

Okay, I'll rework this.

-- 
 Kirill A. Shutemov

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