linux-kernel - [RFC PATCH v2 8/9] mm: Handle COW PTE with reclaim algorithm

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Date:   Wed, 28 Sep 2022 00:29:56 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        William Kucharski <william.kucharski@...cle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Xu <peterx@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Li kunyu <kunyu@...china.com>, Nadav Amit <namit@...are.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Minchan Kim <minchan@...nel.org>,
        Yang Shi <shy828301@...il.com>, Song Liu <song@...nel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Dinglan Peng <peng301@...due.edu>,
        Pedro Fonseca <pfonseca@...due.edu>,
        Jim Huang <jserv@...s.ncku.edu.tw>,
        Huichun Feng <foxhoundsk.tw@...il.com>,
        Chih-En Lin <shiyn.lin@...il.com>
Subject: [RFC PATCH v2 8/9] mm: Handle COW PTE with reclaim algorithm

To avoid the PFRA reclaiming the page resided in the COWed PTE table,
break COW when it using rmap to unmap all the processes.

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 include/linux/rmap.h | 2 ++
 mm/page_vma_mapped.c | 5 +++++
 mm/rmap.c            | 2 +-
 mm/swapfile.c        | 1 +
 mm/vmscan.c          | 1 +
 5 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b89b4b86951f8..5c7e3bedc068b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -312,6 +312,8 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
 #define PVMW_SYNC		(1 << 0)
 /* Look for migration entries rather than present PTEs */
 #define PVMW_MIGRATION		(1 << 1)
+/* Break COW PTE during the walking */
+#define PVMW_COW_PTE		(1 << 2)
 
 struct page_vma_mapped_walk {
 	unsigned long pfn;
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 8e9e574d535aa..5008957bbe4a7 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -251,6 +251,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			step_forward(pvmw, PMD_SIZE);
 			continue;
 		}
+
+		/* TODO: Does breaking COW PTE here is correct? */
+		if (pvmw->flags & PVMW_COW_PTE)
+			handle_cow_pte(vma, pvmw->pmd, pvmw->address, false);
+
 		if (!map_pte(pvmw))
 			goto next_pte;
 this_pte:
diff --git a/mm/rmap.c b/mm/rmap.c
index 93d5a6f793d20..8f737cb44e48a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1477,7 +1477,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		     unsigned long address, void *arg)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
+	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_COW_PTE);
 	pte_t pteval;
 	struct page *subpage;
 	bool anon_exclusive, ret = true;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1fdccd2f1422e..ef4d3d81a824b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1916,6 +1916,7 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 	do {
 		cond_resched();
 		next = pmd_addr_end(addr, end);
+		handle_cow_pte(vma, pmd, addr, false);
 		if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 			continue;
 		ret = unuse_pte_range(vma, pmd, addr, next, type);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b2b1431352dcd..030fad3d310d9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1822,6 +1822,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		/*
 		 * The folio is mapped into the page tables of one or more
 		 * processes. Try to unmap it here.
+		 * It will write to the page tables, break COW PTE here.
 		 */
 		if (folio_mapped(folio)) {
 			enum ttu_flags flags = TTU_BATCH_FLUSH;
-- 
2.37.3