Re: [PATCH v2] mm/shmem.c: make shmem_mapping() inline

[Hui Su]

On Sat, Nov 14, 2020 at 10:50:39AM -0800, Andrew Morton wrote:
> On Sat, 14 Nov 2020 13:51:34 +0800 Hui Su <sh_def@xxxxxxx> wrote:
> 
> > inline the shmem_mapping(), and use shmem_mapping()
> > instead of 'inode->i_mapping->a_ops == &shmem_aops'
> > in shmem_evict_inode().
> > 
> > ...
> >
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1152,7 +1152,7 @@ static void shmem_evict_inode(struct inode *inode)
> >  	struct shmem_inode_info *info = SHMEM_I(inode);
> >  	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
> >  
> > -	if (inode->i_mapping->a_ops == &shmem_aops) {
> > +	if (shmem_mapping(inode->i_mapping)) {
> >  		shmem_unacct_size(info->flags, inode->i_size);
> >  		inode->i_size = 0;
> >  		shmem_truncate_range(inode, 0, (loff_t)-1);
> > @@ -2352,7 +2352,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
> >  	return inode;
> >  }
> >  
> > -bool shmem_mapping(struct address_space *mapping)
> > +inline bool shmem_mapping(struct address_space *mapping)
> >  {
> >  	return mapping->a_ops == &shmem_aops;
> >  }
> 
> huh.  I'd have expected the inlining in shmem_evict_inode() to not work
> because the compiler hasn't seen the definition yet.  But gcc has
> evidently become smarter about that.
> 
> But really, shmem_mapping() isn't worth an out-of-line call from any
> callsite - it would be best to make it inlined everywhere.
> 
> - make shmem_aops global
> - declare shmem_aops in shmem_fs.h
> - export shmem_aops to modules for drivers/dma-buf/udmabuf.c
> - include linux/fs.h in shmem_fs.h for address_space_operations (we already
>   include fs.h via swap.h, but we shouldn't depend on that)
> - make shmem_mapping() a static inline in shmem_fs.h.

Yeah, thanks.

i will resend a PATCH V3 later.