Re: [RFC PATCH v4 3/4] mm: add do_set_pte_range()

[Matthew Wilcox <willy@infradead.org>]

On Mon, Feb 06, 2023 at 05:49:20PM +0100, David Hildenbrand wrote:
> We have
> 
> +	if (!cow) {
> +		folio_add_file_rmap_range(folio, start, nr, vma, false);
> +		add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
> +	} else {
> +		/*
> +		 * rmap code is not ready to handle COW with anonymous
> +		 * large folio yet. Capture and warn if large folio
> +		 * is given.
> +		 */
> +		VM_WARN_ON_FOLIO(folio_test_large(folio), folio);
> +	}
> 
> now.
> 
> What are we supposed to add instead on the else branch instead that would be
> correct in the future? Or not look weird?

Right now, I think this patch should look something like this.

diff --git a/mm/memory.c b/mm/memory.c
index 7a04a1130ec1..2f6173f83d8b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4257,15 +4257,18 @@ 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)
+void set_pte_range(struct vm_fault *vmf, struct folio *folio,
+		struct page *page, unsigned int nr, unsigned long addr)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	bool uffd_wp = pte_marker_uffd_wp(vmf->orig_pte);
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	bool prefault = vmf->address != addr;
 	pte_t entry;
+	unsigned int i;
 
-	flush_icache_page(vma, page);
+	for (i = 0; i < nr; i++)
+		flush_icache_page(vma, page + i);
 	entry = mk_pte(page, vma->vm_page_prot);
 
 	if (prefault && arch_wants_old_prefaulted_pte())
@@ -4279,14 +4282,15 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
 		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);
+		add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr);
+		VM_BUG_ON_FOLIO(folio, nr != 1);
+		folio_add_new_anon_rmap(folio, vma, addr);
+		folio_add_lru_vma(folio, vma);
 	} else {
-		inc_mm_counter(vma->vm_mm, mm_counter_file(page));
-		page_add_file_rmap(page, vma, false);
+		add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
+		folio_add_file_rmap_range(folio, page, nr, vma, false);
 	}
-	set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
+	set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr);
 }
 
 static bool vmf_pte_changed(struct vm_fault *vmf)
@@ -4359,7 +4363,9 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 
 	/* Re-check under ptl */
 	if (likely(!vmf_pte_changed(vmf))) {
-		do_set_pte(vmf, page, vmf->address);
+		struct folio *folio = page_folio(page);
+
+		set_pte_range(vmf, folio, page, 1, vmf->address);
 
 		/* no need to invalidate: a not-present page won't be cached */
 		update_mmu_cache(vma, vmf->address, vmf->pte);

> Go on, scream louder at me, I don't care.

I'm not even shouting.  I just think you're wrong ;-)