From:   Baolin Wang <baolin.wang@linux.alibaba.com>
To:     sj@kernel.org, akpm@linux-foundation.org
Cc:     mike.kravetz@oracle.com, baolin.wang@linux.alibaba.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH v3] mm/damon: Add access checking for hugetlb pages
Date:   Thu, 30 Dec 2021 16:20:28 +0800
Message-Id: <486927ecaaaecf2e3a7fbe0378ec6e1c58b50747.1640852276.git.baolin.wang@linux.alibaba.com>
Precedence: bulk

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@linux.alibaba.com>
---
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