On Tue, Jan 02, 2018 at 02:54:49PM +0800, Sean Fu wrote: > Modify write_page free_buffers and read_page to support circular buffer > list. > > Signed-off-by: Sean Fu <[email protected]> > --- > 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?
