Re: [RFC PATCH v2 4/5] mm: add do_set_pte_range()

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On 01.02.23 09:17, Yin Fengwei wrote:
do_set_pte_range() allows to setup page table entries for a
specific range. It calls page_add_file_rmap_range() to take
advantage of batched rmap update for large folio.

Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
---
  include/linux/mm.h |  2 ++
  mm/filemap.c       |  1 -
  mm/memory.c        | 60 ++++++++++++++++++++++++++++++++++++----------
  3 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d6f8f41514cc..96e08fcdce24 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1162,6 +1162,8 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page);
  void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr);
+void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
+		unsigned long start, unsigned long addr, unsigned int nr);
vm_fault_t finish_fault(struct vm_fault *vmf);
  vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
diff --git a/mm/filemap.c b/mm/filemap.c
index 9cc5edd8f998..95f634d11581 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3386,7 +3386,6 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
ref_count++;
  		do_set_pte(vmf, page, addr);
-		update_mmu_cache(vma, addr, vmf->pte);
  	} while (vmf->pte++, page++, addr += PAGE_SIZE, ++count < nr_pages);
/*
diff --git a/mm/memory.c b/mm/memory.c
index 51c04bb60724..7e41142e1e4f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4257,7 +4257,8 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
  }
  #endif
-void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
+static void do_set_pte_entry(struct vm_fault *vmf, struct page *page,
+		unsigned long addr)
  {
  	struct vm_area_struct *vma = vmf->vma;
  	bool uffd_wp = pte_marker_uffd_wp(vmf->orig_pte);
@@ -4277,16 +4278,52 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
  	if (unlikely(uffd_wp))
  		entry = pte_mkuffd_wp(entry);
-	/* copy-on-write page */
-	if (write && !(vma->vm_flags & VM_SHARED)) {
-		inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
-		page_add_new_anon_rmap(page, vma, addr);
-		lru_cache_add_inactive_or_unevictable(page, vma);
-	} else {
-		inc_mm_counter(vma->vm_mm, mm_counter_file(page));
-		page_add_file_rmap(page, vma, false);
-	}
  	set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
+
+	/* no need to invalidate: a not-present page won't be cached */
+	update_mmu_cache(vma, addr, vmf->pte);
+}
+
+void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
+		unsigned long start, unsigned long addr, unsigned int nr)
+{
+	unsigned int i = 0;
+	struct page *page = folio_page(folio, start);
+	struct vm_area_struct *vma = vmf->vma;
+	bool cow = (vmf->flags & FAULT_FLAG_WRITE) &&
+			!(vma->vm_flags & VM_SHARED);
+
+	/*
+	 * file page: batched update rmap, mm counter.
+	 * copy-on-write page: batched update mm counter.
+	 */
+	if (!cow) {
+		page_add_file_rmap_range(folio, start, nr, vma, false);
+		add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
+	} else
+		add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr);
+
+	do {
+		if (cow) {
+			page_add_new_anon_rmap(page, vma, addr);

This doesn't work with anon pages the way you intended in this patch.

Please leave anon pages out of the picture for now and make do_set_pte_range() only deal with !cow.

--
Thanks,

David / dhildenb





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