[PATCH v2 05/46] rmap: hugetlb: switch from page_dup_file_rmap to page_add_file_rmap

[James Houghton]

This only applies to file-backed HugeTLB, and it should be a no-op until
high-granularity mapping is possible. Also update page_remove_rmap to
support the eventual case where !compound && folio_test_hugetlb().

HugeTLB doesn't use LRU or mlock, so we avoid those bits. This also
means we don't need to use subpage_mapcount; if we did, it would
overflow with only a few mappings.

There is still one caller of page_dup_file_rmap left: copy_present_pte,
and it is always called with compound=false in this case.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 08004371cfed..6c008c9de80e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5077,7 +5077,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 			 * sleep during the process.
 			 */
 			if (!PageAnon(ptepage)) {
-				page_dup_file_rmap(ptepage, true);
+				page_add_file_rmap(ptepage, src_vma, true);
 			} else if (page_try_dup_anon_rmap(ptepage, true,
 							  src_vma)) {
 				pte_t src_pte_old = entry;
@@ -5910,7 +5910,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
 	if (anon_rmap)
 		hugepage_add_new_anon_rmap(folio, vma, haddr);
 	else
-		page_dup_file_rmap(&folio->page, true);
+		page_add_file_rmap(&folio->page, vma, true);
 	new_pte = make_huge_pte(vma, &folio->page, ((vma->vm_flags & VM_WRITE)
 				&& (vma->vm_flags & VM_SHARED)));
 	/*
@@ -6301,7 +6301,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 		goto out_release_unlock;
 
 	if (folio_in_pagecache)
-		page_dup_file_rmap(&folio->page, true);
+		page_add_file_rmap(&folio->page, dst_vma, true);
 	else
 		hugepage_add_new_anon_rmap(folio, dst_vma, dst_addr);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index d3964c414010..b0f87f19b536 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -254,7 +254,7 @@ static bool remove_migration_pte(struct folio *folio,
 				hugepage_add_anon_rmap(new, vma, pvmw.address,
 						       rmap_flags);
 			else
-				page_dup_file_rmap(new, true);
+				page_add_file_rmap(new, vma, true);
 			set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
 		} else
 #endif
diff --git a/mm/rmap.c b/mm/rmap.c
index 15ae24585fc4..c010d0af3a82 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1318,21 +1318,21 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
 	int nr = 0, nr_pmdmapped = 0;
 	bool first;
 
-	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
+	VM_BUG_ON_PAGE(compound && !PageTransHuge(page)
+				&& !folio_test_hugetlb(folio), page);
 
 	/* Is page being mapped by PTE? Is this its first map to be added? */
 	if (likely(!compound)) {
 		first = atomic_inc_and_test(&page->_mapcount);
 		nr = first;
-		if (first && folio_test_large(folio)) {
+		if (first && folio_test_large(folio)
+			  && !folio_test_hugetlb(folio)) {
 			nr = atomic_inc_return_relaxed(mapped);
 			nr = (nr < COMPOUND_MAPPED);
 		}
-	} else if (folio_test_pmd_mappable(folio)) {
-		/* That test is redundant: it's for safety or to optimize out */
-
+	} else {
 		first = atomic_inc_and_test(&folio->_entire_mapcount);
-		if (first) {
+		if (first && !folio_test_hugetlb(folio)) {
 			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
 			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
 				nr_pmdmapped = folio_nr_pages(folio);
@@ -1347,6 +1347,9 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
 		}
 	}
 
+	if (folio_test_hugetlb(folio))
+		return;
+
 	if (nr_pmdmapped)
 		__lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
 			NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
@@ -1376,8 +1379,7 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
 	VM_BUG_ON_PAGE(compound && !PageHead(page), page);
 
 	/* Hugetlb pages are not counted in NR_*MAPPED */
-	if (unlikely(folio_test_hugetlb(folio))) {
-		/* hugetlb pages are always mapped with pmds */
+	if (unlikely(folio_test_hugetlb(folio)) && compound) {
 		atomic_dec(&folio->_entire_mapcount);
 		return;
 	}
@@ -1386,15 +1388,14 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
 	if (likely(!compound)) {
 		last = atomic_add_negative(-1, &page->_mapcount);
 		nr = last;
-		if (last && folio_test_large(folio)) {
+		if (last && folio_test_large(folio)
+			 && !folio_test_hugetlb(folio)) {
 			nr = atomic_dec_return_relaxed(mapped);
 			nr = (nr < COMPOUND_MAPPED);
 		}
-	} else if (folio_test_pmd_mappable(folio)) {
-		/* That test is redundant: it's for safety or to optimize out */
-
+	} else {
 		last = atomic_add_negative(-1, &folio->_entire_mapcount);
-		if (last) {
+		if (last && !folio_test_hugetlb(folio)) {
 			nr = atomic_sub_return_relaxed(COMPOUND_MAPPED, mapped);
 			if (likely(nr < COMPOUND_MAPPED)) {
 				nr_pmdmapped = folio_nr_pages(folio);
@@ -1409,6 +1410,9 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
 		}
 	}
 
+	if (folio_test_hugetlb(folio))
+		return;
+
 	if (nr_pmdmapped) {
 		if (folio_test_anon(folio))
 			idx = NR_ANON_THPS;
-- 
2.39.2.637.g21b0678d19-goog