Re: [PATCH v3 01/17] mm: support madvise(MADV_FREE)

[Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Thu, Nov 12, 2015 at 01:26:20PM +0200, Kirill A. Shutemov wrote:
> On Thu, Nov 12, 2015 at 01:32:57PM +0900, Minchan Kim wrote:
> > @@ -256,6 +260,125 @@ static long madvise_willneed(struct vm_area_struct *vma,
> >  	return 0;
> >  }
> >  
> > +static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> > +				unsigned long end, struct mm_walk *walk)
> > +
> > +{
> > +	struct mmu_gather *tlb = walk->private;
> > +	struct mm_struct *mm = tlb->mm;
> > +	struct vm_area_struct *vma = walk->vma;
> > +	spinlock_t *ptl;
> > +	pte_t *pte, ptent;
> > +	struct page *page;
> > +
> > +	split_huge_page_pmd(vma, addr, pmd);
> > +	if (pmd_trans_unstable(pmd))
> > +		return 0;
> > +
> > +	pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> > +	arch_enter_lazy_mmu_mode();
> > +	for (; addr != end; pte++, addr += PAGE_SIZE) {
> > +		ptent = *pte;
> > +
> > +		if (!pte_present(ptent))
> > +			continue;
> > +
> > +		page = vm_normal_page(vma, addr, ptent);
> > +		if (!page)
> > +			continue;
> > +
> > +		if (PageSwapCache(page)) {
> 
> Could you put VM_BUG_ON_PAGE(PageTransCompound(page), page) here?
> Just in case.

No problem.

> 
> > +			if (!trylock_page(page))
> > +				continue;
> > +
> > +			if (!try_to_free_swap(page)) {
> > +				unlock_page(page);
> > +				continue;
> > +			}
> > +
> > +			ClearPageDirty(page);
> > +			unlock_page(page);
> 
> Hm. Do we handle pages shared over fork() here?
> Souldn't we ignore pages with mapcount > 0?

It was handled later patch by historical reason but it's better
to fold the patch to this.

Thanks for review!