Re: [f2fs-dev] [PATCH v2 10/14] f2fs: handle partial truncate of large folio dirty subpages

[Nanzhe Zhao]

On Thu, 17 Sep 2026 16:30:59 +0800, Chao Yu wrote:
> Since gcing flag is per-folio, so if block #0 is on gcing, but block #1 is
> truncated, it will drop on gcing flag of folio, result in triggering IPU on
> such dirtied block of large folio? also it will affect f2fs_is_cp_guaranteed()?

Hi Chao,

Thanks for the review. I think I may should change like this?

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index f5421334ecf3..a94153be0533 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -351,6 +351,27 @@ static void f2fs_read_end_io(struct bio *bio)
 	f2fs_verify_and_finish_bio(bio, intask);
 }
 
+static bool f2fs_ffs_has_dirty_subpage(struct folio *folio)
+{
+	struct f2fs_folio_state *ffs;
+	unsigned long flags;
+	unsigned int nr_subpages;
+	bool dirty;
+
+	if (!f2fs_folio_has_ffs(folio))
+		return false;
+
+	ffs = (struct f2fs_folio_state *)folio->private;
+	nr_subpages = folio_nr_pages(folio);
+
+	spin_lock_irqsave(&ffs->state_lock, flags);
+	dirty = find_next_bit(ffs->state, 2 * nr_subpages,
+				nr_subpages) < 2 * nr_subpages;
+	spin_unlock_irqrestore(&ffs->state_lock, flags);
+
+	return dirty;
+}
+
 static void f2fs_write_end_bio(struct bio *bio)
 {
 	struct f2fs_sb_info *sbi = bio->bi_private;
@@ -410,7 +431,8 @@ static void f2fs_write_end_bio(struct bio *bio)
 			wake_up(&sbi->cp_wait);
 
 		if (finished) {
-			folio_clear_f2fs_gcing(folio);
+			if (!f2fs_ffs_has_dirty_subpage(folio))
+				folio_clear_f2fs_gcing(folio);
 			folio_end_writeback(folio);
 		}
 	}
@@ -3575,11 +3597,10 @@ static int f2fs_write_single_data_folio(struct folio *folio, int *submitted,
 
 		fio.old_blkaddr = dn.data_blkaddr;
 
 		/* This page is already truncated */
 		if (fio.old_blkaddr == NULL_ADDR) {
 			ffs_clear_subrange_uptodate(folio,
 					i << PAGE_SHIFT, PAGE_SIZE);
-			folio_clear_f2fs_gcing(folio);
 			goto block_done;
 		}
 
@@ -4122,6 +4143,7 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
 		bool verity_in_progress;
 		int folio_submitted = 0;
 		bool bias_added = false;
+		bool dirty;
 
 		submitted = 0;
 		next = true;
@@ -4224,15 +4246,19 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
 		 * partially written back), the folio must stay dirty so that
 		 * the remaining subranges are written back later.
 		 */
-		if (f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
-					(err ? pos : end_pos) - folio_pos(folio)))
+		dirty = f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
+					(err ? pos : end_pos) - folio_pos(folio));
+		if (dirty)
 			folio_redirty_for_writepage(wbc, folio);
 		else
 			inode_dec_dirty_pages(inode);
 
 		if (bias_added) {
-			if (atomic_dec_and_test(&ffs->write_pages_pending))
+			if (atomic_dec_and_test(&ffs->write_pages_pending)) {
+				if (!dirty)
+					folio_clear_f2fs_gcing(folio);
 				folio_end_writeback(folio);
+			}
 		} else if (!folio_submitted && folio_test_writeback(folio)) {
 			folio_end_writeback(folio);
 		}
@@ -5054,6 +5080,8 @@ void f2fs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 			f2fs_remove_dirty_inode(inode);
 			folio_cancel_dirty(folio);
 		}
+		if (!dirty && !folio_test_writeback(folio))
+			folio_clear_f2fs_gcing(folio);
 		return;
 	}
 
-- 
Nanzhe Zhao