Am Sat, 20 May 2017 19:49:53 +0300
schrieb Timofey Titovets <nefelim4ag@xxxxxxxxx>:
> Btrfs already skip store of data where compression didn't free at
> least one byte. So make logic better and make check that compression
> free at least one PAGE_SIZE, because in another case it useless to
> store this data compressed
>
> Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
> ---
> fs/btrfs/lzo.c | 5 ++++-
> fs/btrfs/zlib.c | 3 ++-
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
> index bd0b0938..7f38bc3c 100644
> --- a/fs/btrfs/lzo.c
> +++ b/fs/btrfs/lzo.c
> @@ -229,8 +229,11 @@ static int lzo_compress_pages(struct list_head
> *ws, in_len = min(bytes_left, PAGE_SIZE);
> }
>
> - if (tot_out > tot_in)
> + /* Compression must save at least one PAGE_SIZE */
> + if (tot_out + PAGE_SIZE => tot_in) {
Shouldn't this be ">" instead of ">=" (btw, I don't think => works)...
Given the case that tot_in is 8192, and tot_out is 4096, we saved a
complete page but 4096+4096 would still be equal to 8192.
The former logic only pretended that there is no point in compression
if we saved 0 bytes.
BTW: What's the smallest block size that btrfs stores? Is it always
PAGE_SIZE? I'm not familiar with btrfs internals...
> + ret = -E2BIG;
> goto out;
> + }
>
> /* store the size of all chunks of compressed data */
> cpage_out = kmap(pages[0]);
> diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
> index 135b1082..2b04259b 100644
> --- a/fs/btrfs/zlib.c
> +++ b/fs/btrfs/zlib.c
> @@ -191,7 +191,8 @@ static int zlib_compress_pages(struct list_head
> *ws, goto out;
> }
>
> - if (workspace->strm.total_out >= workspace->strm.total_in) {
> + /* Compression must save at least one PAGE_SIZE */
> + if (workspace->strm.total_out + PAGE_SIZE >=
> workspace->strm.total_in) { ret = -E2BIG;
Same as above...
> goto out;
> }
> --
> 2.13.0
--
Regards,
Kai
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