Re: [PATCH v4 04/12] mm/shmem: Support memfile_notifier

[Chao Peng]

On Tue, Feb 08, 2022 at 08:29:56PM +0200, Mike Rapoport wrote:
> Hi,
> 
> On Tue, Jan 18, 2022 at 09:21:13PM +0800, Chao Peng wrote:
> > It maintains a memfile_notifier list in shmem_inode_info structure and
> > implements memfile_pfn_ops callbacks defined by memfile_notifier. It
> > then exposes them to memfile_notifier via
> > shmem_get_memfile_notifier_info.
> > 
> > We use SGP_NOALLOC in shmem_get_lock_pfn since the pages should be
> > allocated by userspace for private memory. If there is no pages
> > allocated at the offset then error should be returned so KVM knows that
> > the memory is not private memory.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > ---
> >  include/linux/shmem_fs.h |  4 ++
> >  mm/memfile_notifier.c    | 12 +++++-
> >  mm/shmem.c               | 81 ++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 96 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> > index 166158b6e917..461633587eaf 100644
> > --- a/include/linux/shmem_fs.h
> > +++ b/include/linux/shmem_fs.h
> > @@ -9,6 +9,7 @@
> >  #include <linux/percpu_counter.h>
> >  #include <linux/xattr.h>
> >  #include <linux/fs_parser.h>
> > +#include <linux/memfile_notifier.h>
> >  
> >  /* inode in-kernel data */
> >  
> > @@ -24,6 +25,9 @@ struct shmem_inode_info {
> >  	struct shared_policy	policy;		/* NUMA memory alloc policy */
> >  	struct simple_xattrs	xattrs;		/* list of xattrs */
> >  	atomic_t		stop_eviction;	/* hold when working on inode */
> > +#ifdef CONFIG_MEMFILE_NOTIFIER
> > +	struct memfile_notifier_list memfile_notifiers;
> > +#endif
> >  	struct inode		vfs_inode;
> >  };
> >  
> > diff --git a/mm/memfile_notifier.c b/mm/memfile_notifier.c
> > index 8171d4601a04..b4699cbf629e 100644
> > --- a/mm/memfile_notifier.c
> > +++ b/mm/memfile_notifier.c
> > @@ -41,11 +41,21 @@ void memfile_notifier_fallocate(struct memfile_notifier_list *list,
> >  	srcu_read_unlock(&srcu, id);
> >  }
> >  
> > +#ifdef CONFIG_SHMEM
> > +extern int shmem_get_memfile_notifier_info(struct inode *inode,
> > +					struct memfile_notifier_list **list,
> > +					struct memfile_pfn_ops **ops);
> > +#endif
> > +
> >  static int memfile_get_notifier_info(struct inode *inode,
> >  				     struct memfile_notifier_list **list,
> >  				     struct memfile_pfn_ops **ops)
> >  {
> > -	return -EOPNOTSUPP;
> > +	int ret = -EOPNOTSUPP;
> > +#ifdef CONFIG_SHMEM
> > +	ret = shmem_get_memfile_notifier_info(inode, list, ops);
> > +#endif
> 
> This looks backwards. Can we have some register method for memory backing
> store and call it from shmem.c?

Agreed. That would be clearer.

Chao
> 
> > +	return ret;
> >  }
> >  
> >  int memfile_register_notifier(struct inode *inode,
> 
> -- 
> Sincerely yours,
> Mike.