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Date: Mon, 19 Jun 2017 15:21:51 +0200
From: Jan Kara <jack@...e.cz>
To: Sean Fu <fxinrong@...il.com>
Cc: viro@...iv.linux.org.uk, shli@...nel.org, anton@...era.com,
jack@...e.cz, axboe@...com, ebiggers@...gle.com,
rpeterso@...hat.com, bmarzins@...hat.com,
linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-ntfs-dev@...ts.sourceforge.net
Subject: Re: [PATCH] fs: buffer: Modify alloc_page_buffers.
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@...il.com>
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@...e.com>
SUSE Labs, CR
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