[PATCH 2/2] mm: filemap: batch mm counter updating in filemap_map_pages()

[Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>]

Like copy_pte_range()/zap_pte_range(), make mm counter batch updating
in filemap_map_pages(), the 'lat_pagefault -P 1 file' test from lmbench
shows 12% improve, and the percpu_counter_add_batch() is gone from
perf flame graph.

Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 include/linux/mm.h | 14 ++++++++++++++
 mm/filemap.c       | 19 +++++++++++--------
 mm/memory.c        | 14 --------------
 3 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6ad440ac3706..c7dffd358088 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2655,6 +2655,20 @@ static inline int mm_counter(struct folio *folio)
 	return mm_counter_file(folio);
 }
 
+static inline void init_rss_vec(int *rss)
+{
+	memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
+}
+
+static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
+{
+	int i;
+
+	for (i = 0; i < NR_MM_COUNTERS; i++)
+		if (rss[i])
+			add_mm_counter(mm, i, rss[i]);
+}
+
 static inline unsigned long get_mm_rss(struct mm_struct *mm)
 {
 	return get_mm_counter(mm, MM_FILEPAGES) +
diff --git a/mm/filemap.c b/mm/filemap.c
index 2274e590bab4..d8b23e976a43 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3506,7 +3506,7 @@ static struct folio *next_uptodate_folio(struct xa_state *xas,
 static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 			struct folio *folio, unsigned long start,
 			unsigned long addr, unsigned int nr_pages,
-			unsigned int *mmap_miss)
+			int *rss, unsigned int *mmap_miss)
 {
 	vm_fault_t ret = 0;
 	struct page *page = folio_page(folio, start);
@@ -3541,7 +3541,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 skip:
 		if (count) {
 			type = set_pte_range(vmf, folio, page, count, addr);
-			add_mm_counter(vmf->vma->vm_mm, type, count);
+			rss[type] += count;
 			folio_ref_add(folio, count);
 			if (in_range(vmf->address, addr, count * PAGE_SIZE))
 				ret = VM_FAULT_NOPAGE;
@@ -3556,7 +3556,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 
 	if (count) {
 		type = set_pte_range(vmf, folio, page, count, addr);
-		add_mm_counter(vmf->vma->vm_mm, type, count);
+		rss[type] += count;
 		folio_ref_add(folio, count);
 		if (in_range(vmf->address, addr, count * PAGE_SIZE))
 			ret = VM_FAULT_NOPAGE;
@@ -3569,7 +3569,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 
 static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 		struct folio *folio, unsigned long addr,
-		unsigned int *mmap_miss)
+		int *rss, unsigned int *mmap_miss)
 {
 	vm_fault_t ret = 0;
 	struct page *page = &folio->page;
@@ -3592,8 +3592,7 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 	if (vmf->address == addr)
 		ret = VM_FAULT_NOPAGE;
 
-	add_mm_counter(vmf->vma->vm_mm,
-		       set_pte_range(vmf, folio, page, 1, addr), 1);
+	rss[set_pte_range(vmf, folio, page, 1, addr)]++;
 	folio_ref_inc(folio);
 
 	return ret;
@@ -3610,6 +3609,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	XA_STATE(xas, &mapping->i_pages, start_pgoff);
 	struct folio *folio;
 	vm_fault_t ret = 0;
+	int rss[NR_MM_COUNTERS];
 	unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved;
 
 	rcu_read_lock();
@@ -3629,6 +3629,8 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 		folio_put(folio);
 		goto out;
 	}
+
+	init_rss_vec(rss);
 	do {
 		unsigned long end;
 
@@ -3640,15 +3642,16 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 
 		if (!folio_test_large(folio))
 			ret |= filemap_map_order0_folio(vmf,
-					folio, addr, &mmap_miss);
+					folio, addr, rss, &mmap_miss);
 		else
 			ret |= filemap_map_folio_range(vmf, folio,
 					xas.xa_index - folio->index, addr,
-					nr_pages, &mmap_miss);
+					nr_pages, rss, &mmap_miss);
 
 		folio_unlock(folio);
 		folio_put(folio);
 	} while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
+	add_mm_rss_vec(vma->vm_mm, rss);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
 	rcu_read_unlock();
diff --git a/mm/memory.c b/mm/memory.c
index 485ffec9d4c7..149208da1652 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -465,20 +465,6 @@ int __pte_alloc_kernel(pmd_t *pmd)
 	return 0;
 }
 
-static inline void init_rss_vec(int *rss)
-{
-	memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
-}
-
-static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
-{
-	int i;
-
-	for (i = 0; i < NR_MM_COUNTERS; i++)
-		if (rss[i])
-			add_mm_counter(mm, i, rss[i]);
-}
-
 /*
  * This function is called to print an error when a bad pte
  * is found. For example, we might have a PFN-mapped pte in
-- 
2.41.0