Re: [PATCH 6/8] erofs: get rid of fe->backmost for cache decompression

[Gao Xiang]

On 2023/8/18 13:51, Yue Hu wrote:
> On Thu, 17 Aug 2023 16:28:11 +0800
> Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> wrote:
>
> > EROFS_MAP_FULL_MAPPED is more accurate to decide if caching the last
> > incomplete pcluster for later read or not.
> >
> > Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
> > ---
> >   fs/erofs/zdata.c | 7 ++-----
> >   1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> > index 4009283944ca..c28945532a02 100644
> > --- a/fs/erofs/zdata.c
> > +++ b/fs/erofs/zdata.c
> > @@ -528,8 +528,6 @@ struct z_erofs_decompress_frontend {
> >   	z_erofs_next_pcluster_t owned_head;
> >   	enum z_erofs_pclustermode mode;
> >   
> > -	/* used for applying cache strategy on the fly */
> > -	bool backmost;
> >   	erofs_off_t headoffset;
> >   
> >   	/* a pointer used to pick up inplace I/O pages */
> > @@ -538,7 +536,7 @@ struct z_erofs_decompress_frontend {
> >   
> >   #define DECOMPRESS_FRONTEND_INIT(__i) { \
> >   	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
> > -	.mode = Z_EROFS_PCLUSTER_FOLLOWED, .backmost = true }
> > +	.mode = Z_EROFS_PCLUSTER_FOLLOWED }
> >   
> >   static bool z_erofs_should_alloc_cache(struct z_erofs_decompress_frontend *fe)
> >   {
> > @@ -547,7 +545,7 @@ static bool z_erofs_should_alloc_cache(struct z_erofs_decompress_frontend *fe)
> >   	if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
> >   		return false;
> >   
> > -	if (fe->backmost)
> > +	if (!(fe->map.m_flags & EROFS_MAP_FULL_MAPPED))
>
> So, i understand (map.m_flags & EROFS_MAP_FULL_MAPPED) should be false if allocate cache is needed
> (fe->backmost is true)?

fe->backmost is inaccurate compared with !EROFS_MAP_FULL_MAPPED,
if !EROFS_MAP_FULL_MAPPED, it should be cached instead.

Thanks,
Gao Xiang