2 files changed, 52 insertions, 10 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index 4be737055718..bc89c4a30cbc 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -188,6 +188,9 @@ void drbd_bm_unlock(struct drbd_conf *mdev)
 /* to mark for lazy writeout once syncer cleared all clearable bits,
  * we if bits have been cleared since last IO. */
 #define BM_PAGE_LAZY_WRITEOUT   28
+/* pages marked with this "HINT" will be considered for writeout
+ * on activity log transactions */
+#define BM_PAGE_HINT_WRITEOUT   27
 
 /* store_page_idx uses non-atomic assignment. It is only used directly after
  * allocating the page.  All other bm_set_page_* and bm_clear_page_* need to
@@ -237,6 +240,27 @@ static void bm_set_page_need_writeout(struct page *page)
         set_bit(BM_PAGE_NEED_WRITEOUT, &page_private(page));
 }
 
+/**
+ * drbd_bm_mark_for_writeout() - mark a page with a "hint" to be considered for writeout
+ * @mdev:       DRBD device.
+ * @page_nr:    the bitmap page to mark with the "hint" flag
+ *
+ * From within an activity log transaction, we mark a few pages with these
+ * hints, then call drbd_bm_write_hinted(), which will only write out changed
+ * pages which are flagged with this mark.
+ */
+void drbd_bm_mark_for_writeout(struct drbd_conf *mdev, int page_nr)
+{
+        struct page *page;
+        if (page_nr >= mdev->bitmap->bm_number_of_pages) {
+                dev_warn(DEV, "BAD: page_nr: %u, number_of_pages: %u\n",
+                         page_nr, (int)mdev->bitmap->bm_number_of_pages);
+                return;
+        }
+        page = mdev->bitmap->bm_pages[page_nr];
+        set_bit(BM_PAGE_HINT_WRITEOUT, &page_private(page));
+}
+
 static int bm_test_page_unchanged(struct page *page)
 {
         volatile const unsigned long *addr = &page_private(page);
@@ -897,6 +921,7 @@ struct bm_aio_ctx {
         struct completion done;
         unsigned flags;
 #define BM_AIO_COPY_PAGES       1
+#define BM_AIO_WRITE_HINTED     2
         int error;
 };
 
@@ -1007,13 +1032,13 @@ static void bm_page_io_async(struct bm_aio_ctx *ctx, int page_nr, int rw) __must
 /*
  * bm_rw: read/write the whole bitmap from/to its on disk location.
  */
-static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_idx) __must_hold(local)
+static int bm_rw(struct drbd_conf *mdev, int rw, unsigned flags, unsigned lazy_writeout_upper_idx) __must_hold(local)
 {
         struct bm_aio_ctx ctx = {
                 .mdev = mdev,
                 .in_flight = ATOMIC_INIT(1),
                 .done = COMPLETION_INITIALIZER_ONSTACK(ctx.done),
-                .flags = lazy_writeout_upper_idx ? BM_AIO_COPY_PAGES : 0,
+                .flags = flags,
         };
         struct drbd_bitmap *b = mdev->bitmap;
         int num_pages, i, count = 0;
@@ -1042,6 +1067,10 @@ static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_id
                 if (lazy_writeout_upper_idx && i == lazy_writeout_upper_idx)
                         break;
                 if (rw & WRITE) {
+                        if ((flags & BM_AIO_WRITE_HINTED) &&
+                            !test_and_clear_bit(BM_PAGE_HINT_WRITEOUT,
+                                    &page_private(b->bm_pages[i])))
+                                continue;
                         if (bm_test_page_unchanged(b->bm_pages[i])) {
                                 dynamic_dev_dbg(DEV, "skipped bm write for idx %u\n", i);
                                 continue;
@@ -1099,7 +1128,7 @@ static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_id
  */
 int drbd_bm_read(struct drbd_conf *mdev) __must_hold(local)
 {
-        return bm_rw(mdev, READ, 0);
+        return bm_rw(mdev, READ, 0, 0);
 }
 
 /**
@@ -1110,7 +1139,7 @@ int drbd_bm_read(struct drbd_conf *mdev) __must_hold(local)
  */
 int drbd_bm_write(struct drbd_conf *mdev) __must_hold(local)
 {
-        return bm_rw(mdev, WRITE, 0);
+        return bm_rw(mdev, WRITE, 0, 0);
 }
 
 /**
@@ -1120,12 +1149,20 @@ int drbd_bm_write(struct drbd_conf *mdev) __must_hold(local)
  */
 int drbd_bm_write_lazy(struct drbd_conf *mdev, unsigned upper_idx) __must_hold(local)
 {
-        return bm_rw(mdev, WRITE, upper_idx);
+        return bm_rw(mdev, WRITE, BM_AIO_COPY_PAGES, upper_idx);
 }
 
+/**
+ * drbd_bm_write_hinted() - Write bitmap pages with "hint" marks, if they have changed.
+ * @mdev:       DRBD device.
+ */
+int drbd_bm_write_hinted(struct drbd_conf *mdev) __must_hold(local)
+{
+        return bm_rw(mdev, WRITE, BM_AIO_WRITE_HINTED | BM_AIO_COPY_PAGES, 0);
+}
 
 /**
- * drbd_bm_write_page: Writes a PAGE_SIZE aligned piece of bitmap
+ * drbd_bm_write_page() - Writes a PAGE_SIZE aligned piece of bitmap
  * @mdev:       DRBD device.
  * @idx:        bitmap page index
  *
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 93eb3a7ac711..edfdeb62c18f 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1310,11 +1310,14 @@ struct bm_extent {
 
 #define SLEEP_TIME (HZ/10)
 
-#define BM_BLOCK_SHIFT  12                       /* 4k per bit */
+/* We do bitmap IO in units of 4k blocks.
+ * We also still have a hardcoded 4k per bit relation. */
+#define BM_BLOCK_SHIFT  12                       /* 4k per bit */
 #define BM_BLOCK_SIZE    (1<<BM_BLOCK_SHIFT)
-/* (9+3) : 512 bytes @ 8 bits; representing 16M storage
- * per sector of on disk bitmap */
-#define BM_EXT_SHIFT     (BM_BLOCK_SHIFT + MD_SECTOR_SHIFT + 3)  /* = 24 */
+/* mostly arbitrarily set the represented size of one bitmap extent,
+ * aka resync extent, to 16 MiB (which is also 512 Byte worth of bitmap
+ * at 4k per bit resolution) */
+#define BM_EXT_SHIFT     24     /* 16 MiB per resync extent */
 #define BM_EXT_SIZE      (1<<BM_EXT_SHIFT)
 
 #if (BM_EXT_SHIFT != 24) || (BM_BLOCK_SHIFT != 12)
@@ -1408,7 +1411,9 @@ extern int  drbd_bm_test_bit(struct drbd_conf *mdev, unsigned long bitnr);
 extern int  drbd_bm_e_weight(struct drbd_conf *mdev, unsigned long enr);
 extern int  drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local);
 extern int  drbd_bm_read(struct drbd_conf *mdev) __must_hold(local);
+extern void drbd_bm_mark_for_writeout(struct drbd_conf *mdev, int page_nr);
 extern int  drbd_bm_write(struct drbd_conf *mdev) __must_hold(local);
+extern int  drbd_bm_write_hinted(struct drbd_conf *mdev) __must_hold(local);
 extern unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev,
                 unsigned long al_enr);
 extern size_t        drbd_bm_words(struct drbd_conf *mdev);