dm writecache: optimize superblock write

	memset(wc->dirty_bitmap, 0, wc->dirty_bitmap_size);

}

static void ssd_commit_superblock(struct dm_writecache *wc)

{

	int r;

	struct dm_io_region region;

	struct dm_io_request req;

	region.bdev = wc->ssd_dev->bdev;

	region.sector = 0;

	region.count = PAGE_SIZE;

	if (unlikely(region.sector + region.count > wc->metadata_sectors))

		region.count = wc->metadata_sectors - region.sector;

	region.sector += wc->start_sector;

	req.bi_op = REQ_OP_WRITE;

	req.bi_op_flags = REQ_SYNC | REQ_FUA;

	req.mem.type = DM_IO_VMA;

	req.mem.ptr.vma = (char *)wc->memory_map;

	req.client = wc->dm_io;

	req.notify.fn = NULL;

	req.notify.context = NULL;

	r = dm_io(&req, 1, &region, NULL);

	if (unlikely(r))

		writecache_error(wc, r, "error writing superblock");

}

static void writecache_commit_flushed(struct dm_writecache *wc, bool wait_for_ios)

{

	if (WC_MODE_PMEM(wc))

	wc->seq_count++;

	pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count));

	writecache_flush_region(wc, &sb(wc)->seq_count, sizeof sb(wc)->seq_count);

	if (WC_MODE_PMEM(wc))

		writecache_commit_flushed(wc, false);

	else

		ssd_commit_superblock(wc);

	wc->overwrote_committed = false;