[f2fs-dev] [PATCH v3] f2fs: flush cp pack except cp pack 2 page at first

["Gaoxiang (OS)" <gaoxiang25@huawei.com>]

Previously, we attempt to flush the whole cp pack in a single bio,
however, when suddenly powering off at this time, we could get into
an extreme scenario that cp pack 1 page and cp pack 2 page are updated
and latest, but payload or current summaries are still partially
outdated. (see reliable write in the UFS specification)

This patch submits the whole cp pack except cp pack 2 page at first,
and then writes the cp pack 2 page with an extra independent
bio with pre-io barrier.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
Change log from v2:
  - Apply the review comments from Chao
Change log from v1:
  - Apply the review comments from Chao
  - time data from "finish block_ops" to " finish checkpoint" (tested on ARM64 with TOSHIBA 128GB UFS):
     Before patch: 0.002273  0.001973  0.002789  0.005159  0.002050
     After patch: 0.002502  0.001624  0.002487  0.003049  0.002696
 fs/f2fs/checkpoint.c | 39 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 14d2fed..c1f4b10 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -300,6 +300,33 @@ static int f2fs_write_meta_pages(struct address_space *mapping,
 	return 0;
 }
 
+static void commit_checkpoint(struct f2fs_sb_info *sbi,
+	void *src, block_t blk_addr)
+{
+	struct writeback_control wbc = {
+		.for_reclaim = 0,
+	};
+	struct page *page = grab_meta_page(sbi, blk_addr);
+	int err;
+
+	memcpy(page_address(page), src, PAGE_SIZE);
+	set_page_dirty(page);
+
+	f2fs_wait_on_page_writeback(page, META, true);
+	f2fs_bug_on(sbi, PageWriteback(page));
+	if (unlikely(!clear_page_dirty_for_io(page)))
+		f2fs_bug_on(sbi, 1);
+
+	/* writeout cp pack 2 page */
+	err = __f2fs_write_meta_page(page, &wbc, FS_CP_META_IO);
+	f2fs_bug_on(sbi, err);
+
+	f2fs_put_page(page, 0);
+
+	/* submit checkpoint with barrier */
+	f2fs_submit_merged_write(sbi, META_FLUSH);
+}
+
 long sync_meta_pages(struct f2fs_sb_info *sbi, enum page_type type,
 				long nr_to_write, enum iostat_type io_type)
 {
@@ -1297,9 +1324,6 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 		start_blk += NR_CURSEG_NODE_TYPE;
 	}
 
-	/* writeout checkpoint block */
-	update_meta_page(sbi, ckpt, start_blk);
-
 	/* wait for previous submitted node/meta pages writeback */
 	wait_on_all_pages_writeback(sbi);
 
@@ -1313,10 +1337,15 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	sbi->last_valid_block_count = sbi->total_valid_block_count;
 	percpu_counter_set(&sbi->alloc_valid_block_count, 0);
 
-	/* Here, we only have one bio having CP pack */
-	sync_meta_pages(sbi, META_FLUSH, LONG_MAX, FS_CP_META_IO);
+	/* Here, we have one bio having CP pack except cp pack 2 page */
+	sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
 
 	/* wait for previous submitted meta pages writeback */
+	if (!test_opt(sbi, NOBARRIER))
+		wait_on_all_pages_writeback(sbi);
+
+	/* barrier and flush checkpoint cp pack 2 page */
+	commit_checkpoint(sbi, ckpt, start_blk);
 	wait_on_all_pages_writeback(sbi);
 
 	release_ino_entry(sbi, false);
-- 
2.1.4