linux-kernel - Re: [PATCH] erofs(shrinker): return SHRINK

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Message-ID: <AC9D4F55C39C7580+c01e5ccb2bf8f14644d02a84ccc834ad49f86fbb.camel@uniontech.com>
Date: Thu, 16 Jan 2025 16:24:56 +0800
From: Chen Linxuan <chenlinxuan@...ontech.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>, Gao Xiang <xiang@...nel.org>, 
 Chao Yu <chao@...nel.org>, Yue Hu <zbestahu@...il.com>, Jeffle Xu
 <jefflexu@...ux.alibaba.com>,  Sandeep Dhavale <dhavale@...gle.com>
Cc: linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] erofs(shrinker): return SHRINK_EMPTY if no objects to
 free

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@...ontech.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,
> 
> 
>