Re: [f2fs-dev] [PATCH v3 12/17] f2fs: handle partial truncate of large folio dirty subpages

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 10/10/26 00:28, Nanzhe Zhao wrote:
> A large folio can be partial truncated and stays in folio mapping, we
> need to clear the subrange dirty bits and uptodate bits that the partial
> truncate covers. If this partial truncate happens to clear the last
> subrange dirty bits, then cancel the whole folio dirty state.
> 
> Also add a guard in f2fs_write_single_data_folio() so a large folio
> subpage whose disk block was already truncated (NULL_ADDR) is skipped
> 
> Signed-off-by: Nanzhe Zhao <zhaonanzhe@xiaomi.com>
> ---
>   fs/f2fs/data.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 109 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 21c43019167a..138a77044e95 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -329,6 +329,27 @@ 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;
> @@ -380,7 +401,8 @@ 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);
>   		}
>   	}
> @@ -2893,6 +2915,29 @@ static void f2fs_ffs_mark_subrange_uptodate(struct folio *folio, size_t offset,
>   		folio_mark_uptodate(folio);
>   }
>   
> +static void ffs_clear_subrange_uptodate(struct folio *folio,
> +					size_t offset, size_t len)
> +{
> +	struct f2fs_folio_state *ffs;
> +	unsigned int nr_subpages, start, end;
> +	unsigned long flags;
> +
> +	f2fs_bug_on(F2FS_F_SB(folio), offset + len > folio_size(folio));
> +
> +	if (!f2fs_folio_has_ffs(folio))
> +		return;
> +
> +	ffs = (struct f2fs_folio_state *)folio->private;
> +	nr_subpages = folio_nr_pages(folio);
> +	start = offset >> PAGE_SHIFT;
> +	end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
> +	end = min(end, nr_subpages);
> +
> +	spin_lock_irqsave(&ffs->state_lock, flags);
> +	bitmap_clear(ffs->state, start, end - start);
> +	spin_unlock_irqrestore(&ffs->state_lock, flags);
> +}
> +
>   bool f2fs_ffs_test_blk_dirty(const struct folio *folio, pgoff_t index)
>   {
>   	struct f2fs_folio_state *ffs;
> @@ -3771,12 +3816,35 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
>   
>   		err = f2fs_get_dnode_of_data(&dn, data_idx, LOOKUP_NODE);
>   
> +		/*
> +		 * If a subpage of folio for a cow file is dirtied but not
> +		 * reserve a cow block, fallback to original inode to lookup
> +		 * block address

writeback vs truncate on atomic file?

> +		 */
> +		if (atomic_commit && (err == -ENOENT ||
> +		    (!err && dn.data_blkaddr == NULL_ADDR))) {
> +			f2fs_put_dnode(&dn);
> +			set_new_dnode(&dn, inode, NULL, NULL, 0);
> +			err = f2fs_get_dnode_of_data(&dn, data_idx,
> +						     LOOKUP_NODE);
> +			/* Original inode has no block, handled as truncated below */
> +			if (err == -ENOENT)
> +				err = 0;
> +		}
>   		if (err)
>   			goto block_done;
>   		dn_held = true;
>   
>   		fio.old_blkaddr = dn.data_blkaddr;
>   
> +		/* This page is already truncated */
> +		if (fio.old_blkaddr == NULL_ADDR) {
> +			ffs_clear_subrange_uptodate(folio,
> +					(unsigned long long)i << PAGE_SHIFT,

(loff_t)i << PAGE_SHIFT,

Thanks,

> +					PAGE_SIZE);
> +			goto block_done;
> +		}
> +
>   got_it:
>   		if (__is_valid_data_blkaddr(fio.old_blkaddr) &&
>   		    !f2fs_is_valid_blkaddr(sbi, fio.old_blkaddr,
> @@ -4325,6 +4393,7 @@ 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;
> @@ -4432,15 +4501,19 @@ 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 if (!f2fs_folio_has_ffs(folio))
>   			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);
>   		}
> @@ -5243,10 +5316,40 @@ void f2fs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
>   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>   
>   	if (inode->i_ino >= F2FS_ROOT_INO(sbi) &&
> -				(offset || length != folio_size(folio)))
> +				(offset || length != folio_size(folio))) {
> +		size_t clear_start = round_up(offset, PAGE_SIZE);
> +		size_t clear_end = round_down(offset + length, PAGE_SIZE);
> +		size_t clear_length;
> +		bool dirty;
> +
> +		/*
> +		 * If the truncated range falls within a single subpage, no
> +		 * subpage state needs to be cleared.
> +		 */
> +		if (clear_start >= clear_end || !f2fs_folio_has_ffs(folio))
> +			return;
> +
> +		clear_length = clear_end - clear_start;
> +		dirty = f2fs_ffs_clear_subrange_dirty_and_test(folio,
> +						clear_start, clear_length);
> +		ffs_clear_subrange_uptodate(folio, clear_start, clear_length);
> +
> +		/*
> +		 * If the truncated subrange happens to clear the remaining
> +		 * dirty bitmap of the whole folio, cancel the folio-level
> +		 * dirty state.
> +		 */
> +		if (!dirty && folio_test_dirty(folio))
> +			folio_cancel_dirty(folio);
> +		if (!dirty && !folio_test_writeback(folio))
> +			folio_clear_f2fs_gcing(folio);
>   		return;
> +	}
>   
> -	if (folio_test_dirty(folio)) {
> +	if (f2fs_folio_has_ffs(folio)) {
> +		f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
> +							folio_size(folio));
> +	} else if (folio_test_dirty(folio)) {
>   		inode_dec_dirty_pages(inode);
>   		f2fs_remove_dirty_inode(inode);
>   	}



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