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SubjectRe: [PATH] cgroup: add cgroup_favordynmods= command-line option
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On 9/5/23 13:03, Luiz Capitulino wrote:
> On Thu, Aug 31, 2023 at 10:20:46AM -0400, Luiz Capitulino wrote:
>> We have a need of using favordynmods with cgroup v1, which doesn't support
>> changing mount flags during remount. Enabling CONFIG_FAVOR_DYNMODS at
>> build-time is not an option because we want to be able to selectively
>> enable it for certain systems.
>>
>> This commit addresses this by introducing the cgroup_favordynmods=
>> command-line option. This option works for both cgroup v1 and v2 and
>> also allows for disabling favorynmods when the kernel built with
>> CONFIG_FAVOR_DYNMODS=y.
>>
>> Signed-off-by: Luiz Capitulino <luizcap@amazon.com>
> Hi,
>
> Would somebody take a look at this patch please?
>
> Thanks,
>
> - Luiz

The patch looks good to me. I do have a minor comment that it may be
better to use the relatively new __ro_after_init qualifier instead of
__read_mostly.

Cheers,
Longman

>> ---
>> Documentation/admin-guide/kernel-parameters.txt | 4 ++++
>> kernel/cgroup/cgroup.c | 14 +++++++++++---
>> 2 files changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 0c38a8af95ce..672f76a3c002 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -580,6 +580,10 @@
>> named mounts. Specifying both "all" and "named" disables
>> all v1 hierarchies.
>>
>> + cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
>> + Format: { "true" | "false" }
>> + Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
>> +
>> cgroup.memory= [KNL] Pass options to the cgroup memory controller.
>> Format: <string>
>> nosocket -- Disable socket memory accounting.
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index 5fa95f86cb4d..b625825e270b 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -207,6 +207,8 @@ static u16 have_exit_callback __read_mostly;
>> static u16 have_release_callback __read_mostly;
>> static u16 have_canfork_callback __read_mostly;
>>
>> +static bool have_favordynmods __read_mostly = IS_ENABLED(CONFIG_CGROUP_FAVOR_DYNMODS);
>> +
>> /* cgroup namespace for init task */
>> struct cgroup_namespace init_cgroup_ns = {
>> .ns.count = REFCOUNT_INIT(2),
>> @@ -2265,9 +2267,9 @@ static int cgroup_init_fs_context(struct fs_context *fc)
>> fc->user_ns = get_user_ns(ctx->ns->user_ns);
>> fc->global = true;
>>
>> -#ifdef CONFIG_CGROUP_FAVOR_DYNMODS
>> - ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
>> -#endif
>> + if (have_favordynmods)
>> + ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
>> +
>> return 0;
>> }
>>
>> @@ -6767,6 +6769,12 @@ static int __init enable_cgroup_debug(char *str)
>> }
>> __setup("cgroup_debug", enable_cgroup_debug);
>>
>> +static int __init cgroup_favordynmods_setup(char *str)
>> +{
>> + return (kstrtobool(str, &have_favordynmods) == 0);
>> +}
>> +__setup("cgroup_favordynmods=", cgroup_favordynmods_setup);
>> +
>> /**
>> * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
>> * @dentry: directory dentry of interest
>> --
>> 2.40.1
>>

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