Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

[Matthew Wilcox <willy@infradead.org>]

On Mon, Feb 14, 2022 at 09:43:56AM -0800, Stefan Roesch wrote:
> This adds the aop_flags parameter to the create_page_buffers function.
> When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is
> set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are
> enabled.

Why is this better than passing in gfp flags directly?

> Signed-off-by: Stefan Roesch <shr@fb.com>
> ---
>  fs/buffer.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 948505480b43..5e3067173580 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1682,13 +1682,27 @@ static inline int block_size_bits(unsigned int blocksize)
>  	return ilog2(blocksize);
>  }
>  
> -static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
> +static struct buffer_head *create_page_buffers(struct page *page,
> +					struct inode *inode,
> +					unsigned int b_state,
> +					unsigned int aop_flags)
>  {
>  	BUG_ON(!PageLocked(page));
>  
> -	if (!page_has_buffers(page))
> -		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
> -				     b_state);
> +	if (!page_has_buffers(page)) {
> +		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
> +
> +		if (aop_flags & AOP_FLAGS_NOWAIT) {
> +			gfp |= GFP_ATOMIC | __GFP_NOWARN;
> +			gfp &= ~__GFP_DIRECT_RECLAIM;
> +		} else {
> +			gfp |= __GFP_NOFAIL;
> +		}
> +
> +		__create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
> +				     b_state, gfp);
> +	}
> +
>  	return page_buffers(page);
>  }
>  
> @@ -1734,7 +1748,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
>  	int write_flags = wbc_to_write_flags(wbc);
>  
>  	head = create_page_buffers(page, inode,
> -					(1 << BH_Dirty)|(1 << BH_Uptodate));
> +					(1 << BH_Dirty)|(1 << BH_Uptodate), 0);
>  
>  	/*
>  	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
> @@ -2000,7 +2014,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
>  	BUG_ON(to > PAGE_SIZE);
>  	BUG_ON(from > to);
>  
> -	head = create_page_buffers(&folio->page, inode, 0);
> +	head = create_page_buffers(&folio->page, inode, 0, flags);
>  	blocksize = head->b_size;
>  	bbits = block_size_bits(blocksize);
>  
> @@ -2280,7 +2294,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
>  	int nr, i;
>  	int fully_mapped = 1;
>  
> -	head = create_page_buffers(page, inode, 0);
> +	head = create_page_buffers(page, inode, 0, 0);
>  	blocksize = head->b_size;
>  	bbits = block_size_bits(blocksize);
>  
> -- 
> 2.30.2
>