On Thu, Sep 21, 2023 at 4:21 AM Michal Hocko mhocko@suse.com wrote:
On Thu 21-09-23 12:43:05, Jeremi Piotrowski wrote:
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@suse.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,},Of course. I've lost the hunk while massaging the revert. Thanks for spotting. Updated version below. Btw. I've decided to not pr_{warn,info} on the read side because realistically I do not think this will help all that much. I am worried we will get stuck with this for ever because there always be somebody stuck on unpatched userspace.
From bb6702b698efd31f3f90f4f1dd36ffe223397bec Mon Sep 17 00:00:00 2001 From: Michal Hocko mhocko@suse.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.guj3yctzbm1et... Fixes: 86327e8eb94c ("memcg: drop kmem.limit_in_bytes") Fixes: 58056f77502f ("memcg, kmem: further deprecate kmem.limit_in_bytes") Signed-off-by: Michal Hocko mhocko@suse.com
With one request below:
Acked-by: Shakeel Butt shakeelb@google.com
Documentation/admin-guide/cgroup-v1/memory.rst | 7 +++++++ mm/memcontrol.c | 18 ++++++++++++++++++ 2 files changed, 25 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 notsupported since 5.16. Writing any value todo file will not have any effect same as ifnokmem kernel parameter was specified.Kernel memory is still charged and reportedby memory.kmem.usage_in_bytes.diff --git a/mm/memcontrol.c b/mm/memcontrol.c index a4d3282493b6..0b161705ef36 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));
WARN_ON_ONCE() please.