From a2d2574eac3eb153f8503f91197898101d3c86d2 Mon Sep 17 00:00:00 2001
From: Bahadir Balban <bbalban@b-labs.co.uk>
Date: Thu, 30 Oct 2008 11:09:15 +0200
Subject: [PATCH] Added VM_DIRTY flag for file-backed objects and their pages.

Now file flushing in both munmap() and fsync() caters for VM_DIRTY.
Also write_cache_pages() and write faults set this bit on pages and their objects.
---
 tasks/mm0/include/vm_area.h | 4 ++--
 tasks/mm0/src/fault.c       | 8 +++++++-
 tasks/mm0/src/file.c        | 7 +++++++
 tasks/mm0/src/munmap.c      | 5 ++++-
 4 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/tasks/mm0/include/vm_area.h b/tasks/mm0/include/vm_area.h
index e7b803b..f424755 100644
--- a/tasks/mm0/include/vm_area.h
+++ b/tasks/mm0/include/vm_area.h
@@ -51,8 +51,8 @@ enum VM_FILE_TYPE {
 };
 
 /* Defines the type of object. A file? Just a standalone object? */
-#define VM_OBJ_SHADOW		(1 << 8) /* Anonymous pages, swap_pager */
-#define VM_OBJ_FILE		(1 << 9) /* VFS file and device pages */
+#define VM_OBJ_SHADOW		(1 << 10) /* Anonymous pages, swap_pager */
+#define VM_OBJ_FILE		(1 << 11) /* VFS file and device pages */
 
 struct page {
 	int refcnt;		/* Refcount */
diff --git a/tasks/mm0/src/fault.c b/tasks/mm0/src/fault.c
index fa3d468..cc187e5 100644
--- a/tasks/mm0/src/fault.c
+++ b/tasks/mm0/src/fault.c
@@ -677,7 +677,13 @@ int __do_page_fault(struct fault_data *fault)
 					BUG();
 				}
 			}
-			BUG_ON(!page);
+
+			/*
+			 * Page and object are now dirty. Currently it's
+			 * only relevant for file-backed shared objects.
+			 */
+			page->flags |= VM_DIRTY;
+			page->owner->flags |= VM_DIRTY;
 		} else
 			BUG();
 	}
diff --git a/tasks/mm0/src/file.c b/tasks/mm0/src/file.c
index f49f35c..6f21fa0 100644
--- a/tasks/mm0/src/file.c
+++ b/tasks/mm0/src/file.c
@@ -338,6 +338,13 @@ int write_file_pages(struct vm_file *f, unsigned long pfn_start,
 {
 	int err;
 
+	/* We have only thought of vfs files for this */
+	BUG_ON(f->type != VM_FILE_VFS);
+
+	/* Need not flush files that haven't been written */
+	if (!(f->vm_obj.flags & VM_DIRTY))
+		return 0;
+
 	BUG_ON(pfn_end != __pfn(page_align_up(f->length)));
 	for (int f_offset = pfn_start; f_offset < pfn_end; f_offset++) {
 		err = f->vm_obj.pager->ops.page_out(&f->vm_obj, f_offset);
diff --git a/tasks/mm0/src/munmap.c b/tasks/mm0/src/munmap.c
index 7f44fa6..1394667 100644
--- a/tasks/mm0/src/munmap.c
+++ b/tasks/mm0/src/munmap.c
@@ -90,7 +90,6 @@ int vma_flush_pages(struct vm_area *vma)
 	int err;
 
 	/* Read-only vmas need not flush objects */
-	/* FIXME: Ensure pf_handler sets VM_DIRTY on write-faulted pages */
 	if (!(vma->flags & VM_WRITE))
 		return 0;
 
@@ -101,6 +100,10 @@ int vma_flush_pages(struct vm_area *vma)
 	BUG_ON(list_empty(&vma->list));
 	vmo = list_entry(vma->list.next, struct vm_object, list);
 
+	/* Only dirty objects would need flushing */
+	if (!(vmo->flags & VM_DIRTY))
+		return 0;
+
 	/* Only vfs file objects are flushed */
 	if (vmo->flags & VM_OBJ_FILE &&
 	    vmo->flags & VMA_SHARED &&