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

[Mike Rapoport <rppt@kernel.org>]

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@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  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?

> +	return ret;
>  }
>  
>  int memfile_register_notifier(struct inode *inode,

-- 
Sincerely yours,
Mike.