[PATCH] erofs: fix compacted_2b if compacted_4b_initial > totalidx

[Yue Hu]

On Tue, 14 Sep 2021 12:37:14 +0800
Gao Xiang <hsiangkao at linux.alibaba.com> wrote:

> 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"

Yeah, 'clear' is much better for this change.

Thanks.

>  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