Re: [PATCH 10/17] fs: introduce alloc_inode_sb() to allocate filesystems specific inode

[Dave Chinner]

On Tue, May 11, 2021 at 06:46:40PM +0800, Muchun Song wrote:
> The allocated inode cache will be added into its memcg lru list later,
> but we do not allocate list_lru in the later patch. So the caller should
> call kmem_cache_alloc_lru() to allocate inode and related list_lru.
> Introduce alloc_inode_sb() to do that and convert all inodes allocation
> to it.

FWIW, this probably needs a documentation update to mention that
inodes should always be allocated through alloc_inode_sb() rather
than kmem_cache_alloc(). It's a "** mandatory **" requirement as per
Documentation/filesytems/porting.rst.

Also,

> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c3c88fdb9b2a..d8d5d4eb68d6 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -41,6 +41,7 @@
>  #include <linux/stddef.h>
>  #include <linux/mount.h>
>  #include <linux/cred.h>
> +#include <linux/slab.h>
>  
>  #include <asm/byteorder.h>
>  #include <uapi/linux/fs.h>
> @@ -3200,6 +3201,12 @@ extern void free_inode_nonrcu(struct inode *inode);
>  extern int should_remove_suid(struct dentry *);
>  extern int file_remove_privs(struct file *);
>  
> +static inline void *
> +alloc_inode_sb(struct super_block *sb, struct kmem_cache *cache, gfp_t gfp)
> +{
> +	return kmem_cache_alloc_lru(cache, &sb->s_inode_lru, gfp);
> +}
> +

This really needs a kerneldoc comment explaining that it must be
used for allocating inodes to set up the inode reclaim context
correctly....

/me wonders if we should add a BUG_ON() check in inode_init_always()
to capture filesystems that don't call through
kmem_cache_alloc_lru() for inodes?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx