linux-kernel - Re: [RFC PATCH v8 5/7] KVM: guest_memfd: Add slab-allocated inode cache

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Message-ID: <87ecv9ojuh.fsf@DESKTOP-5N7EMDA>
Date: Tue, 24 Jun 2025 12:16:06 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: Shivank Garg <shivankg@....com>
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Subject: Re: [RFC PATCH v8 5/7] KVM: guest_memfd: Add slab-allocated inode
 cache

Shivank Garg <shivankg@....com> writes:

> Add dedicated inode structure (kvm_gmem_inode_info) and slab-allocated
> inode cache for guest memory backing, similar to how shmem handles inodes.
>
> This adds the necessary allocation/destruction functions and prepares
> for upcoming guest_memfd NUMA policy support changes.
>
> Signed-off-by: Shivank Garg <shivankg@....com>
> ---
>  virt/kvm/guest_memfd.c | 51 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 159df462d193..5a1ce6f5e287 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -17,6 +17,15 @@ struct kvm_gmem {
>  	struct list_head entry;
>  };
>  
> +struct kvm_gmem_inode_info {
> +	struct inode vfs_inode;
> +};
> +
> +static inline struct kvm_gmem_inode_info *KVM_GMEM_I(struct inode *inode)
> +{
> +	return container_of(inode, struct kvm_gmem_inode_info, vfs_inode);
> +}
> +
>  /**
>   * folio_file_pfn - like folio_file_page, but return a pfn.
>   * @folio: The folio which contains this index.
> @@ -392,8 +401,33 @@ static struct file_operations kvm_gmem_fops = {
>  	.fallocate	= kvm_gmem_fallocate,
>  };
>  
> +static struct kmem_cache *kvm_gmem_inode_cachep;
> +
> +static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
> +{
> +	struct kvm_gmem_inode_info *info;
> +
> +	info = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
> +	if (!info)
> +		return NULL;
> +
> +	return &info->vfs_inode;
> +}
> +
> +static void kvm_gmem_destroy_inode(struct inode *inode)
> +{
> +}
> +
> +static void kvm_gmem_free_inode(struct inode *inode)
> +{
> +	kmem_cache_free(kvm_gmem_inode_cachep, KVM_GMEM_I(inode));
> +}
> +
>  static const struct super_operations kvm_gmem_super_operations = {
>  	.statfs		= simple_statfs,
> +	.alloc_inode	= kvm_gmem_alloc_inode,
> +	.destroy_inode	= kvm_gmem_destroy_inode,
> +	.free_inode	= kvm_gmem_free_inode,
>  };
>  
>  static int kvm_gmem_init_fs_context(struct fs_context *fc)
> @@ -426,10 +460,26 @@ static int kvm_gmem_init_mount(void)
>  	return 0;
>  }
>  
> +static void kvm_gmem_init_inode(void *foo)
> +{
> +	struct kvm_gmem_inode_info *info = foo;
> +
> +	inode_init_once(&info->vfs_inode);
> +}
> +
> +static void kvm_gmem_init_inodecache(void)
> +{
> +	kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
> +						  sizeof(struct kvm_gmem_inode_info),
> +						  0, SLAB_ACCOUNT,
> +						  kvm_gmem_init_inode);

Check the return value?

And, I'm not a big fan of (logically) one line function encapsulation.

> +}
> +
>  int kvm_gmem_init(struct module *module)
>  {
>  	kvm_gmem_fops.owner = module;
>  
> +	kvm_gmem_init_inodecache();
>  	return kvm_gmem_init_mount();

kmem_cache_destroy(kvm_gmem_inode_cachep) if kvm_gmem_init_mount()
return with error?

>  }
>  
> @@ -437,6 +487,7 @@ void kvm_gmem_exit(void)
>  {
>  	kern_unmount(kvm_gmem_mnt);
>  	kvm_gmem_mnt = NULL;
> +	kmem_cache_destroy(kvm_gmem_inode_cachep);
>  }
>  
>  static int kvm_gmem_migrate_folio(struct address_space *mapping,

---
Best Regards,
Huang, Ying