[PATCH rfc 4/4] mm: filemap: try to batch lruvec stat updating

[Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>]

The filemap_map_pages() tries to map few pages(eg, 16 pages), but the
lruvec stat updating is called on each mapping, since the updating is
time-consuming, especially with memcg, so try to batch it when the memcg
and pgdat are same during the mapping, if luckily, we could save most of
time of lruvec stat updating, the lat_pagefault shows 3~4% improvement.

Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 mm/filemap.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 3966b6616d02..b27281707098 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3615,6 +3615,20 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 	return ret;
 }
 
+static void filemap_lruvec_stat_update(struct mem_cgroup *memcg,
+				       pg_data_t *pgdat, int nr)
+{
+	struct lruvec *lruvec;
+
+	if (!memcg) {
+		__mod_node_page_state(pgdat, NR_FILE_MAPPED, nr);
+		return;
+	}
+
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	__mod_lruvec_state(lruvec, NR_FILE_MAPPED, nr);
+}
+
 vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 			     pgoff_t start_pgoff, pgoff_t end_pgoff)
 {
@@ -3628,6 +3642,9 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	vm_fault_t ret = 0;
 	unsigned long rss = 0;
 	unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved, folio_type;
+	struct mem_cgroup *memcg, *memcg_cur;
+	pg_data_t *pgdat, *pgdat_cur;
+	int nr_mapped = 0;
 
 	rcu_read_lock();
 	folio = next_uptodate_folio(&xas, mapping, end_pgoff);
@@ -3648,9 +3665,20 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	}
 
 	folio_type = mm_counter_file(folio);
+	memcg = folio_memcg(folio);
+	pgdat = folio_pgdat(folio);
 	do {
 		unsigned long end;
-		int nr_mapped = 0;
+
+		memcg_cur = folio_memcg(folio);
+		pgdat_cur = folio_pgdat(folio);
+
+		if (unlikely(memcg != memcg_cur || pgdat != pgdat_cur)) {
+			filemap_lruvec_stat_update(memcg, pgdat, nr_mapped);
+			nr_mapped = 0;
+			memcg = memcg_cur;
+			pgdat = pgdat_cur;
+		}
 
 		addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
 		vmf->pte += xas.xa_index - last_pgoff;
@@ -3668,11 +3696,10 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 					nr_pages, &rss, &nr_mapped,
 					&mmap_miss);
 
-		__lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr_mapped);
-
 		folio_unlock(folio);
 		folio_put(folio);
 	} while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
+	filemap_lruvec_stat_update(memcg, pgdat, nr_mapped);
 	add_mm_counter(vma->vm_mm, folio_type, rss);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 out:
-- 
2.27.0