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Subject[PATCH 1/3] fs: buffer: Create circular buffer list for pages.
Date
Make alloc_page_buffers to create circular buffer list instead linear
list.
Remove unnecessary traversal in link_dev_buffers to create circular
buffer list.
Make nobh_write_begin and nobh_write_end to support circular buffer list
traversal.

Signed-off-by: Sean Fu <fxinrong@gmail.com>
---
fs/buffer.c | 48 +++++++++++++++++++++---------------------------
1 file changed, 21 insertions(+), 27 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 0736a6a..7e62c75 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -842,29 +842,36 @@ int remove_inode_buffers(struct inode *inode)
struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
bool retry)
{
- struct buffer_head *bh, *head;
+ struct buffer_head *bh, *head, *tail;
gfp_t gfp = GFP_NOFS;
long offset;

if (retry)
gfp |= __GFP_NOFAIL;

- head = NULL;
+ head = tail = NULL;
offset = PAGE_SIZE;
while ((offset -= size) >= 0) {
bh = alloc_buffer_head(gfp);
if (!bh)
goto no_grow;

- bh->b_this_page = head;
+ if (unlikely(!head))
+ tail = bh;
+ else
+ bh->b_this_page = head;
+
bh->b_blocknr = -1;
head = bh;
-
bh->b_size = size;

/* Link the buffer to its page */
set_bh_page(bh, page, offset);
}
+
+ if (tail)
+ tail->b_this_page = head;
+
return head;
/*
* In case anything failed, we just free everything we got.
@@ -882,20 +889,6 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
}
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);
-}
-
static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
{
sector_t retval = ~((sector_t)0);
@@ -993,7 +986,7 @@ grow_dev_page(struct block_device *bdev, sector_t block,
* run under the page lock.
*/
spin_lock(&inode->i_mapping->private_lock);
- link_dev_buffers(page, bh);
+ attach_page_buffers(page, bh);
end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
size);
spin_unlock(&inode->i_mapping->private_lock);
@@ -1533,16 +1526,14 @@ 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, true);
bh = head;
do {
bh->b_state |= b_state;
- tail = bh;
bh = bh->b_this_page;
- } while (bh);
- tail->b_this_page = head;
+ } while (bh != head);

spin_lock(&page->mapping->private_lock);
if (PageUptodate(page) || PageDirty(page)) {
@@ -2655,11 +2646,14 @@ int nobh_write_begin(struct address_space *mapping,
* any VM or truncate activity. Hence we don't need to care
* for the buffer_head refcounts.
*/
- for (bh = head; bh; bh = bh->b_this_page) {
+ bh = head;
+ do {
wait_on_buffer(bh);
if (!buffer_uptodate(bh))
ret = -EIO;
- }
+ bh = bh->b_this_page;
+ } while (bh != head);
+
if (ret)
goto failed;
}
@@ -2717,11 +2711,11 @@ int nobh_write_end(struct file *file, struct address_space *mapping,
unlock_page(page);
put_page(page);

- while (head) {
+ do {
bh = head;
head = head->b_this_page;
free_buffer_head(bh);
- }
+ } while (head != fsdata);

return copied;
}
--
2.6.2
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