Hi Yue,
On Fri, Jul 23, 2021 at 11:49:45AM +0800, Yue Hu wrote:
> From: Yue Hu <[email protected]>
>
> Note that count value will be always greater than EROFS_BLKSIZ when
> calling erofs_compress_destsize() in vle_compress_one(). So, the d1
> always >= 1 for compressed block in vle_write_indexes(). That is to
> say tail-end block can't be compressed.
>
> Signed-off-by: Yue Hu <[email protected]>
I once thought tail end block can be compressed with < EROFS_BLKSIZ as
well (as long as it has some benefit) and also tail-packing inline
like uncompressed cases together after compress extents, so that when we
reading the last compress extent meta block, the tail-packing compressed
data can be loaded together.
Currently, I think we could do that, but could you add some DBG_BUGON
like DBG_BUGON(!raw) right above
"type = Z_EROFS_VLE_CLUSTER_TYPE_PLAIN;" and a TODO comment to mention
tail-packing inline compressed cases is under TODO list? That would be
much better.
Thanks,
Gao Xiang
> ---
> lib/compress.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/lib/compress.c b/lib/compress.c
> index af0c720..93fc543 100644
> --- a/lib/compress.c
> +++ b/lib/compress.c
> @@ -73,10 +73,9 @@ static void vle_write_indexes(struct
> z_erofs_vle_compress_ctx *ctx,
>
> di.di_clusterofs = cpu_to_le16(ctx->clusterofs);
>
> - /* whether the tail-end (un)compressed block or not */
> + /* whether the tail-end uncompressed block or not */
> if (!d1) {
> - type = raw ? Z_EROFS_VLE_CLUSTER_TYPE_PLAIN :
> - Z_EROFS_VLE_CLUSTER_TYPE_HEAD;
> + type = Z_EROFS_VLE_CLUSTER_TYPE_PLAIN;
> advise = cpu_to_le16(type << Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT);
>
> di.di_advise = advise;
> --
> 1.9.1
