Re: [PATCH] erofs(shrinker): return SHRINK_EMPTY if no objects to free

[Chen Linxuan <chenlinxuan@uniontech.com>]

On Thu, 2025-01-16 at 15:51 +0800, Gao Xiang wrote:
> Hi Linxuan,
> 
> On 2025/1/16 15:20, Chen Linxuan wrote:
> > Comments in file include/linux/shrinker.h says that
> > `count_objects` of `struct shrinker` should return SHRINK_EMPTY
> > when there are no objects to free.
> > 
> > > If there are no objects to free, it should return SHRINK_EMPTY,
> > > while 0 is returned in cases of the number of freeable items cannot
> > > be determined or shrinker should skip this cache for this time
> > > (e.g., their number is below shrinkable limit).
> 
> Thanks for the patch!
> 
> Yeah, it seems that is the case.  Yet it'd better to document
> what the impact if 0 is returned here if you know more..

Sorry, I have no idea about that.

> 
> > 
> > Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
> > ---
> >   fs/erofs/zutil.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
> > index 0dd65cefce33..682863fa9e1c 100644
> > --- a/fs/erofs/zutil.c
> > +++ b/fs/erofs/zutil.c
> > @@ -243,7 +243,9 @@ void erofs_shrinker_unregister(struct super_block *sb)
> >   static unsigned long erofs_shrink_count(struct shrinker *shrink,
> >   					struct shrink_control *sc)
> >   {
> > -	return atomic_long_read(&erofs_global_shrink_cnt);
> > +	unsigned long count = atomic_long_read(&erofs_global_shrink_cnt);
> > +
> > +	return count ? count : SHRINK_EMPTY;
> 
> I guess you could just use
> 
> 	return atomic_long_read(&erofs_global_shrink_cnt) ?: SHRINK_EMPTY;
> 
> Thanks,
> Gao Xiang
> 
> >   }
> >   
> >   static unsigned long erofs_shrink_scan(struct shrinker *shrink,
> 
> 
>