Re: [PATCH v2] mm/damon: Add access checking for hugetlb pages

[Baolin Wang]

On 12/22/2021 5:10 PM, SeongJae Park wrote:
> Hi Baolin,
>
>
> Basically, the code looks ok to me.  I left so trivial cosmetic nitpicks below,
> though.
>
> On Thu, 16 Dec 2021 18:38:03 +0800 Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>
> > The process's VMAs can be mapped by hugetlb page, but now the DAMON
> > did not implement the access checking for hugetlb pte, so we can not
> > get the actual access count like below if a process VMAs were mapped
> > by hugetlb.
> >
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 4194304-5476352: 0 545
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 140662370467840-140662372970496: 0 545
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 140662372970496-140662375460864: 0 545
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 140662375460864-140662377951232: 0 545
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 140662377951232-140662380449792: 0 545
> > damon_aggregated: target_id=18446614368406014464
> > nr_regions=12 140662380449792-140662382944256: 0 545
> > ......
>
> I'd prefer indenting the program output with 4 spaces and not wrapping it.
> e.g.,
>
>      damon_aggregated: target_id=18446614368406014464 nr_regions=12 4194304-5476352: 0 545
>      damon_aggregated: target_id=18446614368406014464 nr_regions=12 140662370467840-140662372970496: 0 545

Sure.

> > Thus this patch adds hugetlb access checking support, with this patch
> > we can see below VMA mapped by hugetlb access count.
> >
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296486649856-140296489914368: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296489914368-140296492978176: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296492978176-140296495439872: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296495439872-140296498311168: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296498311168-140296501198848: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296501198848-140296504320000: 1 3
> > damon_aggregated: target_id=18446613056935405824
> > nr_regions=12 140296504320000-140296507568128: 1 2
> > ......
>
> ditto.

Sure.

> > +static int damon_mkold_hugetlb_entry(pte_t *pte, unsigned long hmask,
> > +				     unsigned long addr, unsigned long end,
> > +				     struct mm_walk *walk)
> > +{
> > +	struct hstate *h = hstate_vma(walk->vma);
> > +	spinlock_t *ptl;
> > +	pte_t entry;
> > +
> > +	ptl = huge_pte_lock(h, walk->mm, pte);
> > +	entry = huge_ptep_get(pte);
> > +	if (!pte_present(entry))
> > +		goto out;
> > +
> > +	damon_hugetlb_mkold(pte, walk->mm, walk->vma, addr);
> > +
> > +out:
> > +	spin_unlock(ptl);
> > +	return 0;
> > +}
> > +#else
> > +#define damon_mkold_hugetlb_entry NULL
> > +#endif
>
> Could we append a comment saying this #endif is for #ifdef CONFIG_HUGETLB_PAGE,
> like below?
>
>      #endif	/* CONFIG_HUGETLB_PAGE */

Sure.

> > +#ifdef CONFIG_HUGETLB_PAGE
> > +static int damon_young_hugetlb_entry(pte_t *pte, unsigned long hmask,
> > +				     unsigned long addr, unsigned long end,
> > +				     struct mm_walk *walk)
> > +{
> > +	struct damon_young_walk_private *priv = walk->private;
> > +	struct hstate *h = hstate_vma(walk->vma);
> > +	struct page *page;
> > +	spinlock_t *ptl;
> > +	pte_t entry;
> > +
> > +	ptl = huge_pte_lock(h, walk->mm, pte);
> > +	entry = huge_ptep_get(pte);
> > +	if (!pte_present(entry))
> > +		goto out;
> > +
> > +	page = pte_page(entry);
> > +	if (!page)
> > +		goto out;
> > +
> > +	get_page(page);
> > +
> > +	if (pte_young(entry) || !page_is_idle(page) ||
> > +	    mmu_notifier_test_young(walk->mm, addr)) {
> > +		*priv->page_sz = huge_page_size(h);
> > +		priv->young = true;
> > +	}
> > +
> > +	put_page(page);
> > +
> > +out:
> > +	spin_unlock(ptl);
> > +	return 0;
> > +}
> > +#else
> > +#define damon_young_hugetlb_entry NULL
> > +#endif
>
> ditto.

Sure.

But I saw Andrew had applied this version into his branch.

Andrew, would you like me to send a new version? or an increment patch 
to fix the coding style issue? Thanks.