linux-kernel - Re: [PATCH] mm/shmem: use kmem_cache_zalloc in shmem_alloc

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Message-ID: <416a0cb6-fe34-a7ff-6021-92b8dff24f0b@suse.cz>
Date:   Fri, 27 Nov 2020 18:26:23 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hui Su <sh_def@....com>, hughd@...gle.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/shmem: use kmem_cache_zalloc in shmem_alloc_inode()

On 11/15/20 6:40 PM, Hui Su wrote:
> in shmem_get_inode():
> new_inode();
>    new_inode_pseudo();
>      alloc_inode();
>        ops->alloc_inode(); -> shmem_alloc_inode()
>          kmem_cache_alloc();
> 
> memset(info, 0, (char *)inode - (char *)info);
> 
> So use kmem_cache_zalloc() in shmem_alloc_inode(),
> and remove the memset in shmem_get_inode().
> 
> Signed-off-by: Hui Su <sh_def@....com>

Looks correct, but now we clear also the inode part which seems to be handled by 
alloc_inode() well enough. So, unsure. btrfs and ext4 variants don't use kzalloc 
neither. It's also more obvious with the current way that the info is cleared. Hmm?

> ---
>   mm/shmem.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 537c137698f8..b84adda45461 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2308,7 +2308,6 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
>   		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
>   		inode->i_generation = prandom_u32();
>   		info = SHMEM_I(inode);
> -		memset(info, 0, (char *)inode - (char *)info);
>   		spin_lock_init(&info->lock);
>   		atomic_set(&info->stop_eviction, 0);
>   		info->seals = F_SEAL_SEAL;
> @@ -3828,7 +3827,7 @@ static struct kmem_cache *shmem_inode_cachep;
>   static struct inode *shmem_alloc_inode(struct super_block *sb)
>   {
>   	struct shmem_inode_info *info;
> -	info = kmem_cache_alloc(shmem_inode_cachep, GFP_KERNEL);
> +	info = kmem_cache_zalloc(shmem_inode_cachep, GFP_KERNEL);
>   	if (!info)
>   		return NULL;
>   	return &info->vfs_inode;
>