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Date: Thu, 21 Sep 2023 12:43:05 +0200
From: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To: Michal Hocko <mhocko@...e.com>, Shakeel Butt <shakeelb@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Muchun Song <muchun.song@...ux.dev>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, patches@...ts.linux.dev,
Tejun Heo <tj@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, regressions@...ts.linux.dev,
mathieu.tortuyaux@...il.com
Subject: Re: [REGRESSION] Re: [PATCH 6.1 033/219] memcg: drop
kmem.limit_in_bytes
On 9/21/2023 9:52 AM, Michal Hocko wrote:
> On Wed 20-09-23 14:46:52, Shakeel Butt wrote:
>> On Wed, Sep 20, 2023 at 1:08 PM Michal Hocko <mhocko@...e.com> wrote:
>>>
>> [...]
>>>> have a strong opinion against it. Also just to be clear we are not
>>>> talking about full revert of 58056f77502f but just the returning of
>>>> EOPNOTSUPP, right?
>>>
>>> If we allow the limit to be set without returning a failure then we
>>> still have options 2 and 3 on how to deal with that. One of them is to
>>> enforce the limit.
>>>
>>
>> Option 3 is a partial revert of 58056f77502f where we keep the no
>> limit enforcement and remove the EOPNOTSUPP return on write. Let's go
>> with option 3. In addition, let's add pr_warn_once on the read of
>> kmem.limit_in_bytes as well.
>
> How about this?
> ---
I'm OK with this approach. You're missing this in the patch below:
// static struct cftype mem_cgroup_legacy_files[] = {
+ {
+ .name = "kmem.limit_in_bytes",
+ .private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
+ .write = mem_cgroup_write,
+ .read_u64 = mem_cgroup_read_u64,
+ },
Thanks,
Jeremi
>>>From 81ae0797d8da1b9cfbf357b4be4787a5bbf46bb4 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Thu, 21 Sep 2023 09:38:29 +0200
> Subject: [PATCH] mm, memcg: reconsider kmem.limit_in_bytes deprecation
>
> This reverts commits 86327e8eb94c ("memcg: drop kmem.limit_in_bytes")
> and partially reverts 58056f77502f ("memcg, kmem: further deprecate
> kmem.limit_in_bytes") which have incrementally removed support for the
> kernel memory accounting hard limit. Unfortunately it has turned out
> that there is still userspace depending on the existence of
> memory.kmem.limit_in_bytes [1]. The underlying functionality is not
> really required but the non-existent file just confuses the userspace
> which fails in the result. The patch to fix this on the userspace side
> has been submitted but it is hard to predict how it will propagate
> through the maze of 3rd party consumers of the software.
>
> Now, reverting alone 86327e8eb94c is not an option because there is
> another set of userspace which cannot cope with ENOTSUPP returned when
> writing to the file. Therefore we have to go and revisit 58056f77502f
> as well. There are two ways to go ahead. Either we give up on the
> deprecation and fully revert 58056f77502f as well or we can keep
> kmem.limit_in_bytes but make the write a noop and warn about the fact.
> This should work for both known breaking workloads which depend on the
> existence but do not depend on the hard limit enforcement.
>
> [1] http://lkml.kernel.org/r/20230920081101.GA12096@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
> Fixes: 86327e8eb94c ("memcg: drop kmem.limit_in_bytes")
> Fixes: 58056f77502f ("memcg, kmem: further deprecate kmem.limit_in_bytes")
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
> Documentation/admin-guide/cgroup-v1/memory.rst | 7 +++++++
> mm/memcontrol.c | 12 ++++++++++++
> 2 files changed, 19 insertions(+)
>
> diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> index 5f502bf68fbc..ff456871bf4b 100644
> --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> @@ -92,6 +92,13 @@ Brief summary of control files.
> memory.oom_control set/show oom controls.
> memory.numa_stat show the number of memory usage per numa
> node
> + memory.kmem.limit_in_bytes Deprecated knob to set and read the kernel
> + memory hard limit. Kernel hard limit is not
> + supported since 5.16. Writing any value to
> + do file will not have any effect same as if
> + nokmem kernel parameter was specified.
> + Kernel memory is still charged and reported
> + by memory.kmem.usage_in_bytes.
> memory.kmem.usage_in_bytes show current kernel memory allocation
> memory.kmem.failcnt show the number of kernel memory usage
> hits limits
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a4d3282493b6..ac7f14b2338d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3097,6 +3097,7 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
> static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
> unsigned int nr_pages)
> {
> + struct page_counter *counter;
> struct mem_cgroup *memcg;
> int ret;
>
> @@ -3107,6 +3108,10 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
> goto out;
>
> memcg_account_kmem(memcg, nr_pages);
> +
> + /* There is no way to set up kmem hard limit so this operation cannot fail */
> + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> + WARN_ON(!page_counter_try_charge(&memcg->kmem, nr_pages, &counter));
> out:
> css_put(&memcg->css);
>
> @@ -3867,6 +3872,13 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
> case _MEMSWAP:
> ret = mem_cgroup_resize_max(memcg, nr_pages, true);
> break;
> + case _KMEM:
> + pr_warn_once("kmem.limit_in_bytes is deprecated and will be removed. "
> + "Writing any value to this file has no effect. "
> + "Please report your usecase to linux-mm@...ck.org if you "
> + "depend on this functionality.\n");
> + ret = 0;
> + break;
> case _TCP:
> ret = memcg_update_tcp_max(memcg, nr_pages);
> break;
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