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

Hui Su
2020-11-15T16:22:15Z

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@163.com> 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.