On Tue, Jan 02, 2018 at 02:54:49PM +0800, Sean Fu wrote:
quoted hunk ↗ jump to hunk
Modify write_page free_buffers and read_page to support circular buffer
list.
Signed-off-by: Sean Fu <redacted>
---
drivers/md/md-bitmap.c | 36 +++++++++++++++++++-----------------
1 file changed, 19 insertions(+), 17 deletions(-)
diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 239c7bb..b8412c2 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -286,7 +286,7 @@ static void bitmap_file_kick(struct bitmap *bitmap);
*/
static void write_page(struct bitmap *bitmap, struct page *page, int wait)
{
- struct buffer_head *bh;
+ struct buffer_head *bh, *head;
if (bitmap->storage.file == NULL) {
switch (write_sb_page(bitmap, page, wait)) {@@ -295,15 +295,16 @@ static void write_page(struct bitmap *bitmap, struct page *page, int wait)
}
} else {
- bh = page_buffers(page);
+ bh = head = page_buffers(page);
- while (bh && bh->b_blocknr) {
- atomic_inc(&bitmap->pending_writes);
- set_buffer_locked(bh);
- set_buffer_mapped(bh);
- submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
- bh = bh->b_this_page;
- }
+ do {
+ if (bh && bh->b_blocknr) {
+ atomic_inc(&bitmap->pending_writes);
+ set_buffer_locked(bh);
+ set_buffer_mapped(bh);
+ submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
+ }
+ } while ((bh = bh->b_this_page) != head);
if (wait)
wait_event(bitmap->write_wait,@@ -333,17 +334,18 @@ __clear_page_buffers(struct page *page)
}
static void free_buffers(struct page *page)
{
- struct buffer_head *bh;
+ struct buffer_head *bh, *head;
if (!PagePrivate(page))
return;
- bh = page_buffers(page);
- while (bh) {
+ bh = head = page_buffers(page);
+ do {
struct buffer_head *next = bh->b_this_page;
free_buffer_head(bh);
bh = next;
- }
+ } while (bh != head);
+
__clear_page_buffers(page);
put_page(page);
}@@ -362,20 +364,20 @@ static int read_page(struct file *file, unsigned long index,
{
int ret = 0;
struct inode *inode = file_inode(file);
- struct buffer_head *bh;
+ struct buffer_head *bh, *head;
sector_t block;
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, false);
+ bh = head = alloc_page_buffers(page, 1<<inode->i_blkbits, false);
if (!bh) {
ret = -ENOMEM;
goto out;
}
attach_page_buffers(page, bh);
block = index << (PAGE_SHIFT - inode->i_blkbits);
- while (bh) {
+ do {
if (count == 0)
bh->b_blocknr = 0;
else {@@ -400,7 +402,7 @@ static int read_page(struct file *file, unsigned long index,
}
block++;
bh = bh->b_this_page;
- }
+ } while (bh != head);
page->index = index;
wait_event(bitmap->write_wait,
--
2.6.2
Before
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/buffer.o
text data bss dec hex filename
33693 1466 16 35175 8967 fs/buffer.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size drivers/md/md-bitmap.o
text data bss dec hex filename
28149 2168 0 30317 766d drivers/md/md-bitmap.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/ntfs/mft.o
text data bss dec hex filename
2133 36 0 2169 879 fs/ntfs/mft.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/ntfs/aops.o
text data bss dec hex filename
6125 168 0 6293 1895 fs/ntfs/aops.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size vmlinux
text data bss dec hex filename
11480260 5730762 1646084 18857106 11fbc92 vmlinux
sean@linux-zmni:~/sda5/source/linus_repo/linux> size ./arch/x86/boot/bzImage
size: ./arch/x86/boot/bzImage: Warning: Ignoring section flag IMAGE_SCN_MEM_NOT_PAGED in section .bss
text data bss dec hex filename
6571744 0 16975648 23547392 1674e00 ./arch/x86/boot/bzImage
After
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/buffer.o
text data bss dec hex filename
33687 1466 16 35169 8961 fs/buffer.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size drivers/md/md-bitmap.o
text data bss dec hex filename
28221 2168 0 30389 76b5 drivers/md/md-bitmap.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/ntfs/mft.o
text data bss dec hex filename
2133 36 0 2169 879 fs/ntfs/mft.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size fs/ntfs/aops.o
text data bss dec hex filename
6125 168 0 6293 1895 fs/ntfs/aops.o
sean@linux-zmni:~/sda5/source/linus_repo/linux> size vmlinux
text data bss dec hex filename
11480270 5730762 1646084 18857116 11fbc9c vmlinux
sean@linux-zmni:~/sda5/source/linus_repo/linux> size ./arch/x86/boot/bzImage
size: ./arch/x86/boot/bzImage: Warning: Ignoring section flag IMAGE_SCN_MEM_NOT_PAGED in section .bss
text data bss dec hex filename
6571488 0 16975904 23547392 1674e00 ./arch/x86/boot/bzImage
Only patch #3 increases the text section size of drivers/md/md-bitmap.o
The actual text section increment should be several bytes. Duo to compiler align-functions option, the total increment is increased to 72 bytes.
Why is circular list traversal more complex than linear list traversal in this situation?
How to optimize it?