[PATCH] erofs: fix compacted_2b if compacted_4b_initial > totalidx

[Gao Xiang]

On Tue, Sep 14, 2021 at 12:57:48PM +0800, Yue Hu wrote:
> 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.

Ok, I will update this when later applying.

Thanks,
Gao Xiang

> 
> 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