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    SubjectRe: [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@gmail.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@suse.com>
    SUSE Labs, CR

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