Re: [RFC PATCH 0/5] Add inline tail support

[Chao Yu]

On 2024/7/10 9:33, Wu Bo wrote:
> The inode in F2FS occupies an entire 4k block. For many small files, this means
> they consume much more space than their actual size. Therefore, there is
> significant potential to better utilize the inode block space.
>
> Currently, F2FS has two features to make use of the inode block space: inline
> data and inline xattr.
>
> Inline data stores file which size is smaller then 3.5k in inode block. However,
> for slightly larger small files, there still have much waste.
> For example, a 5k file requires 3 blocks, totaling 12k of space, which is
> more than twice the size of the file itself!
>
> Additionally, the end of a file often does not occupy an entire block. If we can
> store the end of the file data within the inode block, we can save an entire
> block for the file. This is particularly important for small files.
>
> In fact, the current inline data is a special case of inline tail, and
> inline tail is an extension of inline data.
>
> To verify the benefits of inline tail, I have developed these preliminary codes.
> To make it simple, inline tail only on small files(<64k). And the layout of
> an inode block is following:
>
> | inode block     | 4096 |     inline tail enable    |
> | --------------- | ---- | --------------------------|
> | inode info      | 360  |                           |
> | --------------- | ---- | --------------------------|
> |                 |      | extra info         | 0~36 |
> |                 |      | **compact_addr[16] | 64   |
> | addr table[923] | 3692 | reserved           | 4    |
> |                 |      | **tail data        |      |
> |                 |      | inline_xattr       | 200  |
> | --------------- | ---- | --------------------------|
> | nid table[5]    | 20   |
> | node footer     | 24   |
>
> I tested inline tail by copying the source code of Linux 6.9.7. The storage
> space was reduced by approximately 8%. Additionally, due to the reduced IO, the
> copy time also reduced by around 10%.

Wu Bo,

Thanks for the effort, but can you please change user-space tools as well?
since this patchset changes layout of inode.

Thanks,

> Wu Bo (5):
>    f2fs: add inline tail mount option
>    f2fs: add inline tail disk layout definition
>    f2fs: implement inline tail write & truncate
>    f2fs: implement inline tail read & fiemap
>    f2fs: set inline tail flag when create inode
>
>   fs/f2fs/data.c   | 61 ++++++++++++++++++++++++++++++++++++++++++++-
>   fs/f2fs/f2fs.h   | 44 ++++++++++++++++++++++++++++++++-
>   fs/f2fs/file.c   | 10 ++++++++
>   fs/f2fs/inline.c | 64 ++++++++++++++++++++++++++++++++----------------
>   fs/f2fs/inode.c  |  6 +++++
>   fs/f2fs/namei.c  |  3 +++
>   fs/f2fs/node.c   |  6 ++++-
>   fs/f2fs/super.c  | 15 ++++++++++++
>   8 files changed, 185 insertions(+), 24 deletions(-)