---- 在 星期五, 2019-10-04 21:20:30 Chengguang Xu <cgxu519@xxxxxxxxxxxx> 撰写 ----
> Current copy-up is not efficient for sparse file,
> It's not only slow but also wasting more disk space
> when the target lower file has huge hole inside.
> This patch tries to recognize file hole and skip it
> during copy-up.
>
> In detail, this optimization checks the hole according
> to copy-up chunk size so it may not recognize all kind
> of holes in the file. However, it is easy to implement
> and will be enough for most of the time.
>
> Additionally, this optimization relies on lseek(2)
> SEEK_DATA implementation, so for some specific
> filesystems which do not support this feature
> will behave as before on copy-up.
>
> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxxxx>
> ---
Any better idea or suggestion for this?
Thanks,
Chengguang
> fs/overlayfs/copy_up.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index b801c6353100..028033c9f021 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -144,10 +144,11 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
> goto out;
> /* Couldn't clone, so now we try to copy the data */
>
> - /* FIXME: copy up sparse files efficiently */
> while (len) {
> size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
> long bytes;
> + loff_t old_next_data_pos;
> + loff_t hole_len;
>
> if (len < this_len)
> this_len = len;
> @@ -157,6 +158,18 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
> break;
> }
>
> + old_next_data_pos = vfs_llseek(old_file, old_pos, SEEK_DATA);
> + if (old_next_data_pos >= old_pos + OVL_COPY_UP_CHUNK_SIZE) {
> + hole_len = (old_next_data_pos - old_pos) /
> + OVL_COPY_UP_CHUNK_SIZE * OVL_COPY_UP_CHUNK_SIZE;
> + old_pos += hole_len;
> + new_pos += hole_len;
> + len -= hole_len;
> + continue;
> + } else if (old_next_data_pos == -ENXIO) {
> + break;
> + }
> +
> bytes = do_splice_direct(old_file, &old_pos,
> new_file, &new_pos,
> this_len, SPLICE_F_MOVE);
> --
> 2.21.0
>
>
>
