Re: [PATCH 1/3] ceph: move to a dedicated slabcache for ceph_cap_snap

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-02-15 at 20:23 +0800, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> There could be huge number of capsnap queued in a short time, on
> x86_64 it's 248 bytes, which will be rounded up to 256 bytes by
> kzalloc. Move this to a dedicated slabcache to save 8 bytes for
> each.
> 
> For the kmalloc-256 slab cache, the actual size will be 512 bytes:
> kmalloc-256        21797  74656    512   32    4 : tunables, etc
> 
> For a dedicated slab cache the real size is 312 bytes:
> ceph_cap_snap          0      0    312   52    4 : tunables, etc
> 
> So actually we can save 200 bytes for each.
> 

I dropped everything but the top paragraph in the description above. On
non-debug kernels, kmalloc-256 is indeed 256 bytes. The inflation you're
seeing is almost certainly from sort of kernel debugging options.

> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>  fs/ceph/snap.c               | 5 +++--
>  fs/ceph/super.c              | 7 +++++++
>  fs/ceph/super.h              | 2 +-
>  include/linux/ceph/libceph.h | 1 +
>  4 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index b41e6724c591..c787775eaf2a 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -482,7 +482,7 @@ static void ceph_queue_cap_snap(struct ceph_inode_info *ci)
>  	struct ceph_buffer *old_blob = NULL;
>  	int used, dirty;
>  
> -	capsnap = kzalloc(sizeof(*capsnap), GFP_NOFS);
> +	capsnap = kmem_cache_alloc(ceph_cap_snap_cachep, GFP_NOFS);
>  	if (!capsnap) {
>  		pr_err("ENOMEM allocating ceph_cap_snap on %p\n", inode);
>  		return;
> @@ -603,7 +603,8 @@ static void ceph_queue_cap_snap(struct ceph_inode_info *ci)
>  	spin_unlock(&ci->i_ceph_lock);
>  
>  	ceph_buffer_put(old_blob);
> -	kfree(capsnap);
> +	if (capsnap)
> +		kmem_cache_free(ceph_cap_snap_cachep, capsnap);
>  	ceph_put_snap_context(old_snapc);
>  }
>  
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index bf79f369aec6..978463fa822c 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -864,6 +864,7 @@ static void destroy_fs_client(struct ceph_fs_client *fsc)
>   */
>  struct kmem_cache *ceph_inode_cachep;
>  struct kmem_cache *ceph_cap_cachep;
> +struct kmem_cache *ceph_cap_snap_cachep;
>  struct kmem_cache *ceph_cap_flush_cachep;
>  struct kmem_cache *ceph_dentry_cachep;
>  struct kmem_cache *ceph_file_cachep;
> @@ -892,6 +893,9 @@ static int __init init_caches(void)
>  	ceph_cap_cachep = KMEM_CACHE(ceph_cap, SLAB_MEM_SPREAD);
>  	if (!ceph_cap_cachep)
>  		goto bad_cap;
> +	ceph_cap_snap_cachep = KMEM_CACHE(ceph_cap_snap, SLAB_MEM_SPREAD);
> +	if (!ceph_cap_snap_cachep)
> +		goto bad_cap_snap;
>  	ceph_cap_flush_cachep = KMEM_CACHE(ceph_cap_flush,
>  					   SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD);
>  	if (!ceph_cap_flush_cachep)
> @@ -931,6 +935,8 @@ static int __init init_caches(void)
>  bad_dentry:
>  	kmem_cache_destroy(ceph_cap_flush_cachep);
>  bad_cap_flush:
> +	kmem_cache_destroy(ceph_cap_snap_cachep);
> +bad_cap_snap:
>  	kmem_cache_destroy(ceph_cap_cachep);
>  bad_cap:
>  	kmem_cache_destroy(ceph_inode_cachep);
> @@ -947,6 +953,7 @@ static void destroy_caches(void)
>  
>  	kmem_cache_destroy(ceph_inode_cachep);
>  	kmem_cache_destroy(ceph_cap_cachep);
> +	kmem_cache_destroy(ceph_cap_snap_cachep);
>  	kmem_cache_destroy(ceph_cap_flush_cachep);
>  	kmem_cache_destroy(ceph_dentry_cachep);
>  	kmem_cache_destroy(ceph_file_cachep);
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index c0718d5a8fb8..2d08104c8955 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -231,7 +231,7 @@ static inline void ceph_put_cap_snap(struct ceph_cap_snap *capsnap)
>  	if (refcount_dec_and_test(&capsnap->nref)) {
>  		if (capsnap->xattr_blob)
>  			ceph_buffer_put(capsnap->xattr_blob);
> -		kfree(capsnap);
> +		kmem_cache_free(ceph_cap_snap_cachep, capsnap);
>  	}
>  }
>  
> diff --git a/include/linux/ceph/libceph.h b/include/linux/ceph/libceph.h
> index edf62eaa6285..00af2c98da75 100644
> --- a/include/linux/ceph/libceph.h
> +++ b/include/linux/ceph/libceph.h
> @@ -284,6 +284,7 @@ DEFINE_RB_LOOKUP_FUNC(name, type, keyfld, nodefld)
>  
>  extern struct kmem_cache *ceph_inode_cachep;
>  extern struct kmem_cache *ceph_cap_cachep;
> +extern struct kmem_cache *ceph_cap_snap_cachep;
>  extern struct kmem_cache *ceph_cap_flush_cachep;
>  extern struct kmem_cache *ceph_dentry_cachep;
>  extern struct kmem_cache *ceph_file_cachep;

-- 
Jeff Layton <jlayton@kernel.org>