Re: [PATCH] fs: buffer: Modify alloc_page_buffers.

[Jan Kara]

On Mon 19-06-17 21:01:36, Sean Fu wrote:
> Make alloc_page_buffers support circular buffer list and initialise
> b_state field.
> Optimize the performance by removing the buffer list traversal to create
> circular buffer list.
> 
> Signed-off-by: Sean Fu <fxinrong@xxxxxxxxx>

IMHO this has unmeasurable performance gain and complicates the code. So I
don't think this is really worth it...

								Honza

> ---
>  drivers/md/bitmap.c         |  2 +-
>  fs/buffer.c                 | 37 +++++++++++++++----------------------
>  fs/ntfs/aops.c              |  2 +-
>  fs/ntfs/mft.c               |  2 +-
>  include/linux/buffer_head.h |  2 +-
>  5 files changed, 19 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> index f4eace5..615a46e 100644
> --- a/drivers/md/bitmap.c
> +++ b/drivers/md/bitmap.c
> @@ -367,7 +367,7 @@ static int read_page(struct file *file, unsigned long index,
>  	pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
>  		 (unsigned long long)index << PAGE_SHIFT);
>  
> -	bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0);
> +	bh = alloc_page_buffers(page, 1<<inode->i_blkbits, 0, 0, 0);
>  	if (!bh) {
>  		ret = -ENOMEM;
>  		goto out;
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 161be58..8111eca 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -864,9 +864,9 @@ int remove_inode_buffers(struct inode *inode)
>   * which may not fail from ordinary buffer allocations.
>   */
>  struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
> -		int retry)
> +		int retry, int circular, unsigned long b_state)
>  {
> -	struct buffer_head *bh, *head;
> +	struct buffer_head *bh, *head, *tail;
>  	long offset;
>  
>  try_again:
> @@ -879,13 +879,21 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
>  
>  		bh->b_this_page = head;
>  		bh->b_blocknr = -1;
> -		head = bh;
>  
> +		if (head == NULL)
> +			tail = bh;
> +
> +		head = bh;
> +		bh->b_state = b_state;
>  		bh->b_size = size;
>  
>  		/* Link the buffer to its page */
>  		set_bh_page(bh, page, offset);
>  	}
> +
> +	if (circular)
> +		tail->b_this_page = head;
> +
>  	return head;
>  /*
>   * In case anything failed, we just free everything we got.
> @@ -922,14 +930,6 @@ EXPORT_SYMBOL_GPL(alloc_page_buffers);
>  static inline void
>  link_dev_buffers(struct page *page, struct buffer_head *head)
>  {
> -	struct buffer_head *bh, *tail;
> -
> -	bh = head;
> -	do {
> -		tail = bh;
> -		bh = bh->b_this_page;
> -	} while (bh);
> -	tail->b_this_page = head;
>  	attach_page_buffers(page, head);
>  }
>  
> @@ -1024,7 +1024,7 @@ grow_dev_page(struct block_device *bdev, sector_t block,
>  	/*
>  	 * Allocate some buffers for this page
>  	 */
> -	bh = alloc_page_buffers(page, size, 0);
> +	bh = alloc_page_buffers(page, size, 0, 1, 0);
>  	if (!bh)
>  		goto failed;
>  
> @@ -1578,16 +1578,9 @@ EXPORT_SYMBOL(block_invalidatepage);
>  void create_empty_buffers(struct page *page,
>  			unsigned long blocksize, unsigned long b_state)
>  {
> -	struct buffer_head *bh, *head, *tail;
> +	struct buffer_head *bh, *head;
>  
> -	head = alloc_page_buffers(page, blocksize, 1);
> -	bh = head;
> -	do {
> -		bh->b_state |= b_state;
> -		tail = bh;
> -		bh = bh->b_this_page;
> -	} while (bh);
> -	tail->b_this_page = head;
> +	head = alloc_page_buffers(page, blocksize, 1, 1, b_state);
>  
>  	spin_lock(&page->mapping->private_lock);
>  	if (PageUptodate(page) || PageDirty(page)) {
> @@ -2642,7 +2635,7 @@ int nobh_write_begin(struct address_space *mapping,
>  	 * Be careful: the buffer linked list is a NULL terminated one, rather
>  	 * than the circular one we're used to.
>  	 */
> -	head = alloc_page_buffers(page, blocksize, 0);
> +	head = alloc_page_buffers(page, blocksize, 0, 0, 0);
>  	if (!head) {
>  		ret = -ENOMEM;
>  		goto out_release;
> diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
> index cc91856..e692142 100644
> --- a/fs/ntfs/aops.c
> +++ b/fs/ntfs/aops.c
> @@ -1739,7 +1739,7 @@ void mark_ntfs_record_dirty(struct page *page, const unsigned int ofs) {
>  	spin_lock(&mapping->private_lock);
>  	if (unlikely(!page_has_buffers(page))) {
>  		spin_unlock(&mapping->private_lock);
> -		bh = head = alloc_page_buffers(page, bh_size, 1);
> +		bh = head = alloc_page_buffers(page, bh_size, 1, 0, 0);
>  		spin_lock(&mapping->private_lock);
>  		if (likely(!page_has_buffers(page))) {
>  			struct buffer_head *tail;
> diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c
> index b6f4021..175a02b 100644
> --- a/fs/ntfs/mft.c
> +++ b/fs/ntfs/mft.c
> @@ -507,7 +507,7 @@ int ntfs_sync_mft_mirror(ntfs_volume *vol, const unsigned long mft_no,
>  	if (unlikely(!page_has_buffers(page))) {
>  		struct buffer_head *tail;
>  
> -		bh = head = alloc_page_buffers(page, blocksize, 1);
> +		bh = head = alloc_page_buffers(page, blocksize, 1, 0, 0);
>  		do {
>  			set_buffer_uptodate(bh);
>  			tail = bh;
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index bd029e52..9a29826 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -155,7 +155,7 @@ void set_bh_page(struct buffer_head *bh,
>  		struct page *page, unsigned long offset);
>  int try_to_free_buffers(struct page *);
>  struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
> -		int retry);
> +		int retry, int circular, unsigned long b_state);
>  void create_empty_buffers(struct page *, unsigned long,
>  			unsigned long b_state);
>  void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
> -- 
> 2.6.2
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR