Re: [PATCH 0/4] memcg: accounting for objects allocated by mkdir cgroup

[Roman Gushchin]

On Fri, May 13, 2022 at 06:51:30PM +0300, Vasily Averin wrote:
> Below is tracing results of mkdir /sys/fs/cgroup/vvs.test on 
> 4cpu VM with Fedora and self-complied upstream kernel. The calculations
> are not precise, it depends on kernel config options, number of cpus,
> enabled controllers, ignores possible page allocations etc.
> However this is enough to clarify the general situation:
> - Total sum of accounted memory is ~60Kb.
> - Accounted only 2 huge percpu allocation marked '=', ~18Kb.
>   (and can be 0 without memory controller)
> - kernfs nodes and iattrs are among the main memory consumers.
>    they are marked '+' to be accounted.
> - cgroup_mkdir always allocates 4Kb,
>    so I think it should be accounted first too.
> - mem_cgroup_css_alloc allocations consumes 10K,
>    it's enough to be accounted, especially for VMs with 1-2 CPUs
> - Almost all other allocations are quite small and can be ignored.
>   Exceptions are percpu allocations in alloc_fair_sched_group(),
>    this can consume a significant amount of memory on nodes
>    with multiple processors.
> - kernfs nodes consumes ~6Kb memory inside simple_xattr_set() 
>    and simple_xattr_alloc(). This is quite high numbers,
>    but is not critical, and I think we can ignore it at the moment.
> - If all proposed memory will be accounted it gives us ~47Kb, 
>    or ~75% of all allocated memory.
> 
> number	bytes	$1*$2	sum	note	call_site
> of	alloc
> allocs
> ------------------------------------------------------------
> 1       14448   14448   14448   =       percpu_alloc_percpu:
> 1       8192    8192    22640   +       (mem_cgroup_css_alloc+0x54)
> 49      128     6272    28912   +       (__kernfs_new_node+0x4e)
> 49      96      4704    33616   ?       (simple_xattr_alloc+0x2c)
> 49      88      4312    37928   +       (__kernfs_iattrs+0x56)
> 1       4096    4096    42024   +       (cgroup_mkdir+0xc7)
> 1       3840    3840    45864   =       percpu_alloc_percpu:
> 4       512     2048    47912   +       (alloc_fair_sched_group+0x166)
> 4       512     2048    49960   +       (alloc_fair_sched_group+0x139)
> 1       2048    2048    52008   +       (mem_cgroup_css_alloc+0x109)
> 49      32      1568    53576   ?       (simple_xattr_set+0x5b)
> 2       584     1168    54744		(radix_tree_node_alloc.constprop.0+0x8d)
> 1       1024    1024    55768           (cpuset_css_alloc+0x30)
> 1       1024    1024    56792           (alloc_shrinker_info+0x79)
> 1       768     768     57560           percpu_alloc_percpu:
> 1       640     640     58200           (sched_create_group+0x1c)
> 33      16      528     58728           (__kernfs_new_node+0x31)
> 1       512     512     59240           (pids_css_alloc+0x1b)
> 1       512     512     59752           (blkcg_css_alloc+0x39)
> 9       48      432     60184           percpu_alloc_percpu:
> 13      32      416     60600           (__kernfs_new_node+0x31)
> 1       384     384     60984           percpu_alloc_percpu:
> 1       256     256     61240           (perf_cgroup_css_alloc+0x1c)
> 1       192     192     61432           percpu_alloc_percpu:
> 1       64      64      61496           (mem_cgroup_css_alloc+0x363)
> 1       32      32      61528           (ioprio_alloc_cpd+0x39)
> 1       32      32      61560           (ioc_cpd_alloc+0x39)
> 1       32      32      61592           (blkcg_css_alloc+0x6b)
> 1       32      32      61624           (alloc_fair_sched_group+0x52)
> 1       32      32      61656           (alloc_fair_sched_group+0x2e)
> 3       8       24      61680           (__kernfs_new_node+0x31)
> 3       8       24      61704           (alloc_cpumask_var_node+0x1b)
> 1       24      24      61728           percpu_alloc_percpu:
> 
> This patch-set enables accounting for required resources.
> I would like to discuss the patches with cgroup developers and maintainers,
> then I'm going re-send approved patches to subsystem maintainers.

Hi Vasily!

Thank you for the analysis and for the series. It looks really good to me.

Please, feel free to add
Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
for the whole series.

Thanks!