[PATCH 08/15] ubifs: Convert ubifs_write_begin() to use a folio

[Zhihao Cheng]

在 2024/1/21 7:08, Matthew Wilcox (Oracle) 写道:
> Save eight calls to compound_head() by using the new folio API.
> Remove a few assumptions that would break with large folios.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
> ---
>   fs/ubifs/file.c | 36 +++++++++++++++++-------------------
>   1 file changed, 17 insertions(+), 19 deletions(-)
> 
> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> index 6302ce65e0b3..ef262499f228 100644
> --- a/fs/ubifs/file.c
> +++ b/fs/ubifs/file.c
> @@ -428,7 +428,7 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
>   	pgoff_t index = pos >> PAGE_SHIFT;
>   	int err, appending = !!(pos + len > inode->i_size);
>   	int skipped_read = 0;
> -	struct page *page;
> +	struct folio *folio;
>   
>   	ubifs_assert(c, ubifs_inode(inode)->ui_size == inode->i_size);
>   	ubifs_assert(c, !c->ro_media && !c->ro_mount);
> @@ -437,13 +437,14 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
>   		return -EROFS;
>   
>   	/* Try out the fast-path part first */
> -	page = grab_cache_page_write_begin(mapping, index);
> -	if (unlikely(!page))
> -		return -ENOMEM;
> +	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
> +			mapping_gfp_mask(mapping));
> +	if (IS_ERR(folio))
> +		return PTR_ERR(folio);
>   
> -	if (!PageUptodate(page)) {
> +	if (!folio_test_uptodate(folio)) {
>   		/* The page is not loaded from the flash */
> -		if (!(pos & ~PAGE_MASK) && len == PAGE_SIZE) {
> +		if (pos == folio_pos(folio) && len >= folio_size(folio)) {

Why not len == folio_size(folio)? Although 'len >= folio_size(folio)' is 
not wrong.

>   			/*
>   			 * We change whole page so no need to load it. But we
>   			 * do not know whether this page exists on the media or
> @@ -453,29 +454,27 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
>   			 * media. Thus, we are setting the @PG_checked flag
>   			 * here.
>   			 */
> -			SetPageChecked(page);
> +			folio_set_checked(folio);
>   			skipped_read = 1;
>   		} else {
> -			err = do_readpage(page);
> +			err = do_readpage(&folio->page);
>   			if (err) {
> -				unlock_page(page);
> -				put_page(page);
> +				folio_unlock(folio);
> +				folio_put(folio);
>   				return err;
>   			}
>   		}
>   	}
>   
> -	err = allocate_budget(c, page, ui, appending);
> +	err = allocate_budget(c, &folio->page, ui, appending);
>   	if (unlikely(err)) {
>   		ubifs_assert(c, err == -ENOSPC);
>   		/*
>   		 * If we skipped reading the page because we were going to
>   		 * write all of it, then it is not up to date.
>   		 */
> -		if (skipped_read) {
> -			ClearPageChecked(page);
> -			ClearPageUptodate(page);
> -		}
> +		if (skipped_read)
> +			folio_clear_checked(folio);
>   		/*
>   		 * Budgeting failed which means it would have to force
>   		 * write-back but didn't, because we set the @fast flag in the
> @@ -487,8 +486,8 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
>   			ubifs_assert(c, mutex_is_locked(&ui->ui_mutex));
>   			mutex_unlock(&ui->ui_mutex);
>   		}
> -		unlock_page(page);
> -		put_page(page);
> +		folio_unlock(folio);
> +		folio_put(folio);
>   
>   		return write_begin_slow(mapping, pos, len, pagep);
>   	}
> @@ -499,9 +498,8 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
>   	 * with @ui->ui_mutex locked if we are appending pages, and unlocked
>   	 * otherwise. This is an optimization (slightly hacky though).
>   	 */
> -	*pagep = page;
> +	*pagep = &folio->page;
>   	return 0;
> -
>   }
>   
>   /**
>