Re: [PATCH v3] mm/damon: Add access checking for hugetlb pages

[SeongJae Park]

On Thu, 30 Dec 2021 16:20:28 +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
> ......
> 
> 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
> ......
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

In addition to unwrapping program outputs in commit message, I personally
prefer indenting those with 4 spaces[1], but I wouldn't bother you for such a
trivial thing.  Thank you for this patch!

Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>

[1] https://lore.kernel.org/linux-mm/17421c73-2124-63c2-1925-dcea5c976711@xxxxxxxxxxxxxxxxx/


Thanks,
SJ

> ---
> Changes from v2:
>  - Change commit messages to be more readable
>  - Add comments for config macro.
>  - Fix unused variable compiling warning.
> 
> Changes from v1:
>  - Move damon_hugetlb_mkold() to vaddr.c file.
>  - Move some assignments in the variables definitions.
> ---
>  mm/damon/vaddr.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 96 insertions(+)
> 
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index a10df3f..ee465b3 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -388,8 +388,65 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
>  	return 0;
>  }
>  
> +#ifdef CONFIG_HUGETLB_PAGE
> +static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
> +				struct vm_area_struct *vma, unsigned long addr)
> +{
> +	bool referenced = false;
> +	pte_t entry = huge_ptep_get(pte);
> +	struct page *page = pte_page(entry);
> +
> +	if (!page)
> +		return;
> +
> +	get_page(page);
> +
> +	if (pte_young(entry)) {
> +		referenced = true;
> +		entry = pte_mkold(entry);
> +		huge_ptep_set_access_flags(vma, addr, pte, entry,
> +					   vma->vm_flags & VM_WRITE);
> +	}
> +
> +#ifdef CONFIG_MMU_NOTIFIER
> +	if (mmu_notifier_clear_young(mm, addr,
> +				     addr + huge_page_size(hstate_vma(vma))))
> +		referenced = true;
> +#endif /* CONFIG_MMU_NOTIFIER */
> +
> +	if (referenced)
> +		set_page_young(page);
> +
> +	set_page_idle(page);
> +	put_page(page);
> +}
> +
> +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 /* CONFIG_HUGETLB_PAGE */
> +
>  static const struct mm_walk_ops damon_mkold_ops = {
>  	.pmd_entry = damon_mkold_pmd_entry,
> +	.hugetlb_entry = damon_mkold_hugetlb_entry,
>  };
>  
>  static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
> @@ -484,8 +541,47 @@ static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
>  	return 0;
>  }
>  
> +#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 /* CONFIG_HUGETLB_PAGE */
> +
>  static const struct mm_walk_ops damon_young_ops = {
>  	.pmd_entry = damon_young_pmd_entry,
> +	.hugetlb_entry = damon_young_hugetlb_entry,
>  };
>  
>  static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
> -- 
> 1.8.3.1
> 
> 
>