[RFC PATCH v2 5/5] filemap: batched update mm counter,rmap when map file folio

[Yin Fengwei <fengwei.yin@xxxxxxxxx>]

Use do_set_pte_range() in filemap_map_folio_range(). Which
batched updates mm counter, rmap.

With a self cooked will-it-scale.page_fault3 like app (change
file write fault to read fault) got 15% performance gain.

Perf data collected before/after the change:
  18.73%--page_add_file_rmap
          |
           --11.60%--__mod_lruvec_page_state
                     |
                     |--7.40%--__mod_memcg_lruvec_state
                     |          |
                     |           --5.58%--cgroup_rstat_updated
                     |
                      --2.53%--__mod_lruvec_state
                                |
                                 --1.48%--__mod_node_page_state

  9.93%--page_add_file_rmap_range
         |
          --2.67%--__mod_lruvec_page_state
                    |
                    |--1.95%--__mod_memcg_lruvec_state
                    |          |
                    |           --1.57%--cgroup_rstat_updated
                    |
                     --0.61%--__mod_lruvec_state
                               |
                                --0.54%--__mod_node_page_state

The running time of __mode_lruvec_page_state() is reduced a lot.

Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
---
 mm/filemap.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 95f634d11581..b14f077d1c55 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3364,11 +3364,22 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 	struct file *file = vma->vm_file;
 	struct page *page = folio_page(folio, start);
 	unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
-	unsigned int ref_count = 0, count = 0;
+	unsigned int ref_count = 0, count = 0, nr_mapped = 0;
 
 	do {
-		if (PageHWPoison(page))
+		if (PageHWPoison(page)) {
+			if (nr_mapped) {
+				vmf->pte -= nr_mapped;
+				do_set_pte_range(vmf, folio,
+						start + count - nr_mapped,
+						addr - nr_mapped * PAGE_SIZE,
+						nr_mapped);
+
+			}
+
+			nr_mapped = 0;
 			continue;
+		}
 
 		if (mmap_miss > 0)
 			mmap_miss--;
@@ -3378,16 +3389,34 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 		 * handled in the specific fault path, and it'll prohibit the
 		 * fault-around logic.
 		 */
-		if (!pte_none(*vmf->pte))
+		if (!pte_none(*vmf->pte)) {
+			if (nr_mapped) {
+				vmf->pte -= nr_mapped;
+				do_set_pte_range(vmf, folio,
+						start + count - nr_mapped,
+						addr - nr_mapped * PAGE_SIZE,
+						nr_mapped);
+
+			}
+
+			nr_mapped = 0;
+
 			continue;
+		}
 
 		if (vmf->address == addr)
 			ret = VM_FAULT_NOPAGE;
 
 		ref_count++;
-		do_set_pte(vmf, page, addr);
+		nr_mapped++;
 	} while (vmf->pte++, page++, addr += PAGE_SIZE, ++count < nr_pages);
 
+	if (nr_mapped) {
+		vmf->pte -= nr_mapped;
+		do_set_pte_range(vmf, folio, start + count - nr_mapped,
+				addr - nr_mapped * PAGE_SIZE, nr_mapped);
+	}
+
 	/*
 	 * Restore the vmf->pte. Otherwise, it's possible vmf->pte point
 	 * to next page table entry if the last sub page in the range is
-- 
2.30.2