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Subject[PATCH 11/15] drbd: allow to select specific bitmap pages for writeout
Date
From: Lars Ellenberg <lars.ellenberg@linbit.com>

We are about to allow several changes to the active set in one activity
log transaction. We have to write out the corresponding bitmap pages as
well, if changed.

Introduce drbd_bm_mark_for_writeout(), then re-use the existing bitmap
writeout path to submit all marked pages in one go.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
---
drivers/block/drbd/drbd_bitmap.c | 43 ++++++++++++++++++++++++++++++++-----
drivers/block/drbd/drbd_int.h | 13 ++++++++---
2 files changed, 46 insertions(+), 10 deletions(-)
diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index 4be7370..2d00a8f 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 +240,21 @@ 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 = 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 +915,7 @@ 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 +1026,13 @@ 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 +1061,10 @@ 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 +1122,7 @@ 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 +1133,7 @@ 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 +1143,20 @@ 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 de92e8b..f125c0e 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);
--
1.7.4.1


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