linux-kernel - Re: [PATCH mm v2 2/9] memcg: enable accounting for kernfs nodes

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Message-ID: <YonaOq6jrGygwbcH@FVFYT0MHHV2J.usts.net>
Date:   Sun, 22 May 2022 14:37:46 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Vasily Averin <vvs@...nvz.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Koutný <mkoutny@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH mm v2 2/9] memcg: enable accounting for kernfs nodes

On Sat, May 21, 2022 at 07:37:49PM +0300, Vasily Averin wrote:
> kernfs nodes are quite small kernel objects, however there are few
> scenarios where it consumes significant piece of all allocated memory:
> 
> 1) creating a new netdevice allocates ~50Kb of memory, where ~10Kb
>    was allocated for 80+ kernfs nodes.
> 
> 2) cgroupv2 mkdir allocates ~60Kb of memory, ~10Kb of them are kernfs
>    structures.
> 
> 3) Shakeel Butt reports that Google has workloads which create 100s
>    of subcontainers and they have observed high system overhead
>    without memcg accounting of kernfs.
> 
> Usually new kernfs node creates few other objects:
> 
> Allocs  Alloc   Allocation
> number  size
> --------------------------------------------
> 1   +  128      (__kernfs_new_node+0x4d)	kernfs node
> 1   +   88      (__kernfs_iattrs+0x57)		kernfs iattrs
> 1   +   96      (simple_xattr_alloc+0x28)	simple_xattr, can grow over 4Kb
> 1       32      (simple_xattr_set+0x59)
> 1       8       (__kernfs_new_node+0x30)
> 
> '+' -- to be accounted
> 
> This patch enables accounting for kernfs nodes slab cache.
> 
> Signed-off-by: Vasily Averin <vvs@...nvz.org>

Reviewed-by: Muchun Song <songmuchun@...edance.com>