linux-kernel - [PATCH v2] mm: add access/dirty bit on numa page fault

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Message-Id: <20220317065033.2635123-1-maobibo@loongson.cn>
Date:   Thu, 17 Mar 2022 02:50:33 -0400
From:   Bibo Mao <maobibo@...ngson.cn>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v2] mm: add access/dirty bit on numa page fault

On platforms like x86/arm which supports hw page walking, access
and dirty bit is set by hw, however on some platforms without
such hw functions, access and dirty bit is set by software in
next trap.

During numa page fault, dirty bit can be added for old pte if
fail to migrate on write fault. And if it succeeds to migrate,
access bit can be added for migrated new pte, also dirty bit
can be added for write fault.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 mm/memory.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index c125c4969913..65813bec9c06 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4404,6 +4404,22 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	if (migrate_misplaced_page(page, vma, target_nid)) {
 		page_nid = target_nid;
 		flags |= TNF_MIGRATED;
+
+		/*
+		 * update pte entry with access bit, and dirty bit for
+		 * write fault
+		 */
+		spin_lock(vmf->ptl);
+		pte = *vmf->pte;
+		pte = pte_mkyoung(pte);
+		if (was_writable) {
+			pte = pte_mkwrite(pte);
+			if (vmf->flags & FAULT_FLAG_WRITE)
+				pte = pte_mkdirty(pte);
+		}
+		set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
+		update_mmu_cache(vma, vmf->address, vmf->pte);
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
 	} else {
 		flags |= TNF_MIGRATE_FAIL;
 		vmf->pte = pte_offset_map(vmf->pmd, vmf->address);
@@ -4427,8 +4443,11 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	old_pte = ptep_modify_prot_start(vma, vmf->address, vmf->pte);
 	pte = pte_modify(old_pte, vma->vm_page_prot);
 	pte = pte_mkyoung(pte);
-	if (was_writable)
+	if (was_writable) {
 		pte = pte_mkwrite(pte);
+		if (vmf->flags & FAULT_FLAG_WRITE)
+			pte = pte_mkdirty(pte);
+	}
 	ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte);
 	update_mmu_cache(vma, vmf->address, vmf->pte);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
-- 
2.31.1