Message-ID: <20210715220505.GQ22357@magnolia>
Date:   Thu, 15 Jul 2021 15:05:05 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v14 106/138] iomap: Convert iomap_do_writepage to use a
 folio

On Thu, Jul 15, 2021 at 04:36:32AM +0100, Matthew Wilcox (Oracle) wrote:
> Writeback an entire folio at a time, and adjust some of the variables
> to have more familiar names.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/iomap/buffered-io.c | 49 +++++++++++++++++++-----------------------
>  1 file changed, 22 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8e767aec8d07..0731e2c3f44b 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1296,9 +1296,8 @@ iomap_add_to_ioend(struct inode *inode, loff_t pos, struct folio *folio,
>  static int
>  iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  		struct writeback_control *wbc, struct inode *inode,
> -		struct page *page, u64 end_offset)
> +		struct folio *folio, loff_t end_pos)
>  {
> -	struct folio *folio = page_folio(page);
>  	struct iomap_page *iop = to_iomap_page(folio);
>  	struct iomap_ioend *ioend, *next;
>  	unsigned len = i_blocksize(inode);
> @@ -1316,7 +1315,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	 * invalid, grab a new one.
>  	 */
>  	for (i = 0; i < nblocks; i++, pos += len) {
> -		if (pos >= end_offset)
> +		if (pos >= end_pos)
>  			break;
>  		if (iop && !test_bit(i, iop->uptodate))
>  			continue;
> @@ -1398,16 +1397,15 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  static int
>  iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)

I imagine at some point this will become iomap_do_writefolio and ther
will be some sort of write_cache_folios() call?  Or the equivalent
while(get_next_folio_to_wrote()) iomap_write_folio(); type loop?

Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

>  {
> +	struct folio *folio = page_folio(page);
>  	struct iomap_writepage_ctx *wpc = data;
> -	struct inode *inode = page->mapping->host;
> -	pgoff_t end_index;
> -	u64 end_offset;
> -	loff_t offset;
> +	struct inode *inode = folio->mapping->host;
> +	loff_t end_pos, isize;
>  
> -	trace_iomap_writepage(inode, page_offset(page), PAGE_SIZE);
> +	trace_iomap_writepage(inode, folio_pos(folio), folio_size(folio));
>  
>  	/*
> -	 * Refuse to write the page out if we are called from reclaim context.
> +	 * Refuse to write the folio out if we are called from reclaim context.
>  	 *
>  	 * This avoids stack overflows when called from deeply used stacks in
>  	 * random callers for direct reclaim or memcg reclaim.  We explicitly
> @@ -1421,10 +1419,10 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  		goto redirty;
>  
>  	/*
> -	 * Is this page beyond the end of the file?
> +	 * Is this folio beyond the end of the file?
>  	 *
> -	 * The page index is less than the end_index, adjust the end_offset
> -	 * to the highest offset that this page should represent.
> +	 * The folio index is less than the end_index, adjust the end_pos
> +	 * to the highest offset that this folio should represent.
>  	 * -----------------------------------------------------
>  	 * |			file mapping	       | <EOF> |
>  	 * -----------------------------------------------------
> @@ -1433,11 +1431,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  	 * |     desired writeback range    |      see else    |
>  	 * ---------------------------------^------------------|
>  	 */
> -	offset = i_size_read(inode);
> -	end_index = offset >> PAGE_SHIFT;
> -	if (page->index < end_index)
> -		end_offset = (loff_t)(page->index + 1) << PAGE_SHIFT;
> -	else {
> +	isize = i_size_read(inode);
> +	end_pos = folio_pos(folio) + folio_size(folio);
> +	if (end_pos - 1 >= isize) {
>  		/*
>  		 * Check whether the page to write out is beyond or straddles
>  		 * i_size or not.
> @@ -1449,7 +1445,8 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  		 * |				    |      Straddles     |
>  		 * ---------------------------------^-----------|--------|
>  		 */
> -		unsigned offset_into_page = offset & (PAGE_SIZE - 1);
> +		size_t poff = offset_in_folio(folio, isize);
> +		pgoff_t end_index = isize >> PAGE_SHIFT;
>  
>  		/*
>  		 * Skip the page if it is fully outside i_size, e.g. due to a
> @@ -1468,8 +1465,8 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  		 * if the page to write is totally beyond the i_size or if it's
>  		 * offset is just equal to the EOF.
>  		 */
> -		if (page->index > end_index ||
> -		    (page->index == end_index && offset_into_page == 0))
> +		if (folio->index > end_index ||
> +		    (folio->index == end_index && poff == 0))
>  			goto redirty;
>  
>  		/*
> @@ -1480,17 +1477,15 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
>  		 * memory is zeroed when mapped, and writes to that region are
>  		 * not written out to the file."
>  		 */
> -		zero_user_segment(page, offset_into_page, PAGE_SIZE);
> -
> -		/* Adjust the end_offset to the end of file */
> -		end_offset = offset;
> +		zero_user_segment(&folio->page, poff, folio_size(folio));
> +		end_pos = isize;
>  	}
>  
> -	return iomap_writepage_map(wpc, wbc, inode, page, end_offset);
> +	return iomap_writepage_map(wpc, wbc, inode, folio, end_pos);
>  
>  redirty:
> -	redirty_page_for_writepage(wbc, page);
> -	unlock_page(page);
> +	folio_redirty_for_writepage(wbc, folio);
> +	folio_unlock(folio);
>  	return 0;
>  }
>  
> -- 
> 2.30.2
> 

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