linux-kernel - Re: [PATCH 2/4] memcg: enable accounting for kernfs nodes and iattrs

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Date:   Thu, 19 May 2022 18:33:00 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Vasily Averin <vvs@...nvz.org>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH 2/4] memcg: enable accounting for kernfs nodes and iattrs

On Fri, May 13, 2022 at 06:51:55PM +0300, Vasily Averin <vvs@...nvz.org> wrote:
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index cfa79715fc1a..40e896c7c86b 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -391,10 +391,12 @@ void __init kernfs_init(void)
>  {
>  	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
>  					      sizeof(struct kernfs_node),
> -					      0, SLAB_PANIC, NULL);
> +					      0, SLAB_PANIC | SLAB_ACCOUNT,
> +					      NULL);
>  
>  	/* Creates slab cache for kernfs inode attributes */
>  	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
>  					      sizeof(struct kernfs_iattrs),
> -					      0, SLAB_PANIC, NULL);
> +					      0, SLAB_PANIC | SLAB_ACCOUNT,
> +					      NULL);

IIUC your stats report, struct kernfs_iattrs is mere 88B (per
kernfs_node), when considering attributes, I actually thought of
something like:

--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -950,7 +950,7 @@ struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
        if (len < sizeof(*new_xattr))
                return NULL;

-       new_xattr = kvmalloc(len, GFP_KERNEL);
+       new_xattr = kvmalloc(len, GFP_KERNEL_ACCOUNT);
        if (!new_xattr)
                return NULL;

Again, I'd split the patch into two: kernfs_node and
kernfs_iattrs+simple_xattr for easier bisecting.

Thanks,
Michal