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Date: Sun, 27 Feb 2011 14:37:06 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: tytso@....edu, sandeen@...hat.com, adilger@...ger.ca
Cc: linux-ext4@...r.kernel.org, Yongqiang Yang <xiaoqiangnk@...il.com>
Subject: Re: [PATCH] ext4:Make FIEMAP and delayed allocation play well together.
Hi,
This patch passes xfstest 225 with Eric's patches.
http://oss.sgi.com/pipermail/xfs/2011-February/049525.html
http://oss.sgi.com/pipermail/xfs/2011-February/049527.html
On Sun, Feb 27, 2011 at 2:38 PM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> 1. lookup dirty pages with specified range in pagecache.
> If no page is got, then there is no delayed-extent and
> return with EXT_CONTINUE.
> 2. find the 1st mapped buffer,
> 3. check if the mapped buffer is both in the request range
> and a delayed buffer. If not, there is no delayed-extent,
> then return.
> 4. a delayed-extent is found, the extent will be collected.
>
> Reported by Chris Mason <chris.mason@...cle.com>:
> We've had reports on btrfs that cp is giving us files full of zeros
> instead of actually copying them. It was tracked down to a bug with
> the btrfs fiemap implementation where it was returning holes for
> delalloc ranges.
>
> Newer versions of cp are trusting fiemap to tell it where the holes
> are, which does seem like a pretty neat trick.
>
> I decided to give xfs and ext4 a shot with a few tests cases too, xfs
> passed with all the ones btrfs was getting wrong, and ext4 got the basic
> delalloc case right.
> $ mkfs.ext4 /dev/xxx
> $ mount /dev/xxx /mnt
> $ dd if=/dev/zero of=/mnt/foo bs=1M count=1
> $ fiemap-test foo
> ext: 0 logical: [ 0.. 255] phys: 0.. 255
> flags: 0x007 tot: 256
>
> Horray! But once we throw a hole in, things go bad:
> $ mkfs.ext4 /dev/xxx
> $ mount /dev/xxx /mnt
> $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=1
> $ fiemap-test foo
> < no output >
>
> We've got a delalloc extent after the hole and ext4 fiemap didn't find
> it. If I run sync to kick the delalloc out:
> $sync
> $ fiemap-test foo
> ext: 0 logical: [ 256.. 511] phys: 34048.. 34303
> flags: 0x001 tot: 256
>
> fiemap-test is sitting in my /usr/local/bin, and I have no idea how it
> got there. It's full of pretty comments so I know it isn't mine, but
> you can grab it here:
>
> http://oss.oracle.com/~mason/fiemap-test.c
>
> xfsqa has a fiemap program too.
>
> After Fix, test results are as follows:
> ext: 0 logical: [ 256.. 511] phys: 0.. 255
> flags: 0x007 tot: 256
> ext: 0 logical: [ 256.. 511] phys: 33280.. 33535
> flags: 0x001 tot: 256
>
> $ mkfs.ext4 /dev/xxx
> $ mount /dev/xxx /mnt
> $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=1
> $ sync
> $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=3
> $ dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=5
> $ fiemap-test foo
> ext: 0 logical: [ 256.. 511] phys: 33280.. 33535
> flags: 0x000 tot: 256
> ext: 1 logical: [ 768.. 1023] phys: 0.. 255
> flags: 0x006 tot: 256
> ext: 2 logical: [ 1280.. 1535] phys: 0.. 255
> flags: 0x007 tot: 256
>
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
> ---
> fs/ext4/extents.c | 187 ++++++++++++++++++++++++++++++++++++++++++-----------
> 1 files changed, 148 insertions(+), 39 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index ccce8a7..402a7e8 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3775,6 +3775,7 @@ int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
> }
> return ret > 0 ? ret2 : ret;
> }
> +
> /*
> * Callback function called for each extent to gather FIEMAP information.
> */
> @@ -3782,38 +3783,162 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
> struct ext4_ext_cache *newex, struct ext4_extent *ex,
> void *data)
> {
> - struct fiemap_extent_info *fieinfo = data;
> - unsigned char blksize_bits = inode->i_sb->s_blocksize_bits;
> __u64 logical;
> __u64 physical;
> __u64 length;
> + loff_t size;
> __u32 flags = 0;
> - int error;
> + int ret = 0;
> + struct fiemap_extent_info *fieinfo = data;
> + unsigned char blksize_bits;
>
> - logical = (__u64)newex->ec_block << blksize_bits;
> + blksize_bits = inode->i_sb->s_blocksize_bits;
> + logical = (__u64)newex->ec_block << blksize_bits;
>
> if (newex->ec_start == 0) {
> - pgoff_t offset;
> - struct page *page;
> + /*
> + * No extent in extent-tree contains block @newex->ec_start,
> + * then the block may stay in 1)a hole or 2)delayed-extent.
> + *
> + * Holes or delayed-extents are processed as follows.
> + * 1. lookup dirty pages with specified range in pagecache.
> + * If no page is got, then there is no delayed-extent and
> + * return with EXT_CONTINUE.
> + * 2. find the 1st mapped buffer,
> + * 3. check if the mapped buffer is both in the request range
> + * and a delayed buffer. If not, there is no delayed-extent,
> + * then return.
> + * 4. a delayed-extent is found, the extent will be collected.
> + */
> + ext4_lblk_t end = 0;
> + pgoff_t last_offset;
> + pgoff_t offset;
> + pgoff_t index;
> + struct page **pages = NULL;
> struct buffer_head *bh = NULL;
> + struct buffer_head *head = NULL;
> + unsigned int nr_pages = PAGE_SIZE / sizeof(struct page *);
> +
> + pages = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + if (pages == NULL)
> + return -EFAULT;
>
> offset = logical >> PAGE_SHIFT;
> - page = find_get_page(inode->i_mapping, offset);
> - if (!page || !page_has_buffers(page))
> - return EXT_CONTINUE;
> +repeat:
> + last_offset = offset;
> + head = NULL;
> + ret = find_get_pages_tag(inode->i_mapping, &offset,
> + PAGECACHE_TAG_DIRTY, nr_pages, pages);
> +
> + if (!(flags & FIEMAP_EXTENT_DELALLOC)) {
> + /* First time, try to find a mapped buffer. */
> + if (ret == 0) {
> +out:
> + for (index = 0; index < ret; index++)
> + page_cache_release(pages[index]);
> + /* just a hole. */
> + kfree(pages);
> + return EXT_CONTINUE;
> + }
>
> - bh = page_buffers(page);
> + /* Try to find the 1st mapped buffer. */
> + end = ((__u64)pages[0]->index << PAGE_SHIFT) >>
> + blksize_bits;
> + if (!page_has_buffers(pages[0]))
> + goto out;
> + head = page_buffers(pages[0]);
> + if (!head)
> + goto out;
>
> - if (!bh)
> - return EXT_CONTINUE;
> + bh = head;
> + do {
> + if (buffer_mapped(bh)) {
> + /* get the 1st mapped buffer. */
> + if (end > newex->ec_block +
> + newex->ec_len)
> + /* The buffer is out of
> + * the request range.
> + */
> + goto out;
> + goto found_mapped_buffer;
> + }
> + bh = bh->b_this_page;
> + end++;
> + } while (bh != head);
>
> - if (buffer_delay(bh)) {
> - flags |= FIEMAP_EXTENT_DELALLOC;
> - page_cache_release(page);
> + /* No mapped buffer found. */
> + goto out;
> } else {
> - page_cache_release(page);
> - return EXT_CONTINUE;
> + /*Find contiguous delayed buffers. */
> + if (ret > 0 && pages[0]->index == last_offset)
> + head = page_buffers(pages[0]);
> + bh = head;
> + }
> +
> +found_mapped_buffer:
> + if (bh != NULL && buffer_delay(bh)) {
> + /* 1st or contiguous delayed buffer found. */
> + if (!(flags & FIEMAP_EXTENT_DELALLOC)) {
> + /*
> + * 1st delayed buffer found, record
> + * the start of extent.
> + */
> + flags |= FIEMAP_EXTENT_DELALLOC;
> + newex->ec_block = end;
> + logical = (__u64)end << blksize_bits;
> + }
> + /* Find contiguous delayed buffers. */
> + do {
> + if (!buffer_delay(bh))
> + goto found_delayed_extent;
> + bh = bh->b_this_page;
> + end++;
> + } while (bh != head);
> +
> + for (index = 1; index < ret; index++) {
> + if (!page_has_buffers(pages[index])) {
> + bh = NULL;
> + break;
> + }
> + head = page_buffers(pages[index]);
> + if (!head) {
> + bh = NULL;
> + break;
> + }
> + if (pages[index]->index !=
> + pages[0]->index + index) {
> + /* Blocks are not contiguous. */
> + bh = NULL;
> + break;
> + }
> + bh = head;
> + do {
> + if (!buffer_delay(bh))
> + /* Delayed-extent ends. */
> + goto found_delayed_extent;
> + bh = bh->b_this_page;
> + end++;
> + } while (bh != head);
> + }
> + } else if (!(flags & FIEMAP_EXTENT_DELALLOC))
> + /* a hole found. */
> + goto out;
> +
> +found_delayed_extent:
> + newex->ec_len = min(end - newex->ec_block,
> + (ext4_lblk_t)EXT_INIT_MAX_LEN);
> + if (ret == nr_pages && bh != NULL &&
> + newex->ec_len < EXT_INIT_MAX_LEN &&
> + buffer_delay(bh)) {
> + /* Have not collected an extent and continue. */
> + for (index = 0; index < ret; index++)
> + page_cache_release(pages[index]);
> + goto repeat;
> }
> +
> + for (index = 0; index < ret; index++)
> + page_cache_release(pages[index]);
> + kfree(pages);
> }
>
> physical = (__u64)newex->ec_start << blksize_bits;
> @@ -3822,32 +3947,16 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
> if (ex && ext4_ext_is_uninitialized(ex))
> flags |= FIEMAP_EXTENT_UNWRITTEN;
>
> - /*
> - * If this extent reaches EXT_MAX_BLOCK, it must be last.
> - *
> - * Or if ext4_ext_next_allocated_block is EXT_MAX_BLOCK,
> - * this also indicates no more allocated blocks.
> - *
> - * XXX this might miss a single-block extent at EXT_MAX_BLOCK
> - */
> - if (ext4_ext_next_allocated_block(path) == EXT_MAX_BLOCK ||
> - newex->ec_block + newex->ec_len - 1 == EXT_MAX_BLOCK) {
> - loff_t size = i_size_read(inode);
> - loff_t bs = EXT4_BLOCK_SIZE(inode->i_sb);
> -
> + size = i_size_read(inode);
> + if (logical + length >= size)
> flags |= FIEMAP_EXTENT_LAST;
> - if ((flags & FIEMAP_EXTENT_DELALLOC) &&
> - logical+length > size)
> - length = (size - logical + bs - 1) & ~(bs-1);
> - }
>
> - error = fiemap_fill_next_extent(fieinfo, logical, physical,
> + ret = fiemap_fill_next_extent(fieinfo, logical, physical,
> length, flags);
> - if (error < 0)
> - return error;
> - if (error == 1)
> + if (ret < 0)
> + return ret;
> + if (ret == 1)
> return EXT_BREAK;
> -
> return EXT_CONTINUE;
> }
>
> --
> 1.7.4
>
>
--
Best Wishes
Yongqiang Yang
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