[PATCH] erofs: fix compacted_2b if compacted_4b_initial > totalidx

[Gao Xiang]

On Tue, Sep 14, 2021 at 11:59:15AM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2 at yulong.com>
> 
> Currently, the whole indexes will only be compacted 4B if
> compacted_4b_initial > totalidx. So, the calculated compacted_2b
> is worthless for that case. It may waste CPU resources.
> 
> No need to update compacted_4b_initial as mkfs since it's used to
> fulfill the alignment of the 1st compacted_2b pack and would handle
> the case above.
> 
> We also need to clarify compacted_4b_end here. It's used for the
> last lclusters which aren't fitted in the previous compacted_2b
> packs.
> 
> Some messages are from Xiang.
> 
> Signed-off-by: Yue Hu <huyue2 at yulong.com>

Looks good to me,
Reviewed-by: Gao Xiang <hsiangkao at linux.alibaba.com>

(although I think the subject title would be better changed into
 "clear compacted_2b if compacted_4b_initial > totalidx"
 since 'fix'-likewise words could trigger some AI bot for stable
 kernel backporting..)

Thanks,
Gao Xiang

> ---
>  fs/erofs/zmap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> index 9fb98d8..aeed404 100644
> --- a/fs/erofs/zmap.c
> +++ b/fs/erofs/zmap.c
> @@ -369,7 +369,8 @@ static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
>  	if (compacted_4b_initial == 32 / 4)
>  		compacted_4b_initial = 0;
>  
> -	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
> +	if ((vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B) &&
> +	    compacted_4b_initial <= totalidx) {
>  		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
>  	else
>  		compacted_2b = 0;
> -- 
> 1.9.1