Re: [PATCH] erofs: remove unneeded icur field from struct z_erofs_decompress_frontend

[Gao Xiang]

On 2023/4/17 14:52, Gao Xiang wrote:
> On 2023/4/17 14:41, Yue Hu wrote:
> > From: Yue Hu <huyue2@xxxxxxxxxxx>
> >
> > The icur field is only used in z_erofs_try_inplace_io(). Let's just use
> > a local variable instead. And no need to check if the pcluster is inline
> > when setting icur since inline page cannot be used for inplace I/O.

Where do we check if the pcluster is inline?

> > Signed-off-by: Yue Hu <huyue2@xxxxxxxxxxx>
>
> Nope, it's a behavior change.
> Other users could feed more inplace I/O pages before I/O submission
> to reduce memory consumption, it's common when applying stress model
> in low memory scenarios.

Oh, I misread it.  I think it can be done in this way although
each following users will now rescan the whole array all the time.

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

> Thanks,
> Gao Xiang
>
> > ---
> >   fs/erofs/zdata.c | 13 +++++--------
> >   1 file changed, 5 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> > index f759152feffa..f8bf2b227942 100644
> > --- a/fs/erofs/zdata.c
> > +++ b/fs/erofs/zdata.c
> > @@ -554,9 +554,6 @@ struct z_erofs_decompress_frontend {
> >       /* used for applying cache strategy on the fly */
> >       bool backmost;
> >       erofs_off_t headoffset;
> > -
> > -    /* a pointer used to pick up inplace I/O pages */
> > -    unsigned int icur;
> >   };
> >   #define DECOMPRESS_FRONTEND_INIT(__i) { \
> > @@ -707,11 +704,13 @@ static bool z_erofs_try_inplace_io(struct z_erofs_decompress_frontend *fe,
> >                      struct z_erofs_bvec *bvec)
> >   {
> >       struct z_erofs_pcluster *const pcl = fe->pcl;
> > +    /* file-backed online pages are traversed in reverse order */

Although please help refine the comment below:

	/* scan & fill inplace I/O pages in the reverse order */

Thanks,
Gao Xiang

> > +    unsigned int icur = pcl->pclusterpages;
> > -    while (fe->icur > 0) {
> > -        if (!cmpxchg(&pcl->compressed_bvecs[--fe->icur].page,
> > +    while (icur > 0) {
> > +        if (!cmpxchg(&pcl->compressed_bvecs[--icur].page,
> >                    NULL, bvec->page)) {
> > -            pcl->compressed_bvecs[fe->icur] = *bvec;
> > +            pcl->compressed_bvecs[icur] = *bvec;
> >               return true;
> >           }
> >       }
> > @@ -877,8 +876,6 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
> >       }
> >       z_erofs_bvec_iter_begin(&fe->biter, &fe->pcl->bvset,
> >                   Z_EROFS_INLINE_BVECS, fe->pcl->vcnt);
> > -    /* since file-backed online pages are traversed in reverse order */
> > -    fe->icur = z_erofs_pclusterpages(fe->pcl);
> >       return 0;
> >   }