[LTP] [PATCH v3 3/7] Add new CGroups APIs

[Richard Palethorpe <rpalethorpe@suse.de>]

Li Wang <liwang@redhat.com> writes:

> Hi,
>
>>> -enum tst_cgroup_ctrl {
>> >> -    TST_CGROUP_MEMCG = 1,
>> >> +/* Controller sub-systems */
>> >> +enum tst_cgroup_css {
>> >> +    TST_CGROUP_MEMORY = 1,
>> >>      TST_CGROUP_CPUSET = 2,
>> >> -    /* add cgroup controller */
>> >>  };
>> >
>> > I spend a bit of time figuring out what css means, can't we just use
>> > controler in the code instead? It's a bit longer but more obvious.
>> >
>> > Or is this consitent with kernel naming?
>>
>> The kernel seems to refer to controllers as subsystems and css appears
>> to mean "CGroup subsystem". I'm not sure if subsystems are necessarily
>> controllers, but it seems that way. Also "controller" has too many
>> letters in it. Indeed it makes some function names very long and I found
>> that harder to read.
>
>
> I also feel css looks oddly, if "controller" is too long we can go back
> with "ctrl",
> then we might need a one-line comment for the name abbreviation.
>
> e.g.  previous "/* add cgroup controller */" is make no sense but a hint
> for people
> to know this is cgroup controller and could be extended in the future.

OK ctrl it is and I will create a note about internal kernel naming.

>
>
>> I suppose to be totally consistent with the kernel we should randomly
>> name some things css and others subsys. :-p
>>
>
> Not very necessary, this test API is facing for userland,
> understanding easily
> for users is more important I think.
>
>
>>> +struct tst_cgroup_opts {
>> >> +    /* Only try to mount V1 CGroup controllers. This will not
>> >> +     * prevent V2 from being used if it is already mounted, it
>> >> +     * only indicates that we should mount V1 controllers if
>> >> +     * nothing is present. By default we try to mount V2 first. */
>> >> +    int only_mount_v1:1;
>> >> +};
>> >
>> > Do we need to pass the flags in a structure?
>> >
>> > This is not an API that has to be future proof, when we find out we need
>> > more than a few bitflags we can always change it.
>>
>> We may need to add xattr to this and there are many other
>> options. However most tests will just have NULL or 0, 0... So we could
>> move it into a vararg or have a tst_require2?
>>
>
> My 2cent:
>
> I slightly think tst_cgroup_opts is good stuff, it gives a possibility
> to let users hook the cgoup mount way or, more options they
> needed (maybe for customized users). And, in most situations
> that test just has NULL, that's fine.

+1

>
> @Richard,
> do you want to reserve the ?no_cleanup? in this structure as well?
> I noticed you leave it in tst_cgroup02 test.

I think this is only necessary if we add a new flag to all tests in
tst_test to prevent CGroup cleanup. It should be easy to add this in a
later patch.

>
>
>
>> >> +    struct tst_cgroup_tree *trees[TST_CGROUP_MAX_TREES + 1];
>> >> +};
>> >
>> > So this is an array of directories in different trees, can we please
>> > name the strucuture better. What about tst_cgroup_nodes or
>> > tst_cgroup_dirs?
>>
>> I guess tst_cgroup_tree always represents a directory. So I would go
>> with tst_cgroup_dir.
>>
>
> +1
>
>>> +struct tst_cgroup_tree {
>> >
>> > Why isn't this called node or dir? Either of these would be more
>> > fitting.
>> >
>> > Also the tst_cgroup structure could use a better name, the tst_cgroup is
>> > actually an array of pointers to directories.
>>
>> As far as the test author is concerned it represents an actual "Control
>> Group". We keep arrays of directories to join together multiple V1
>> controllers on different hierarchies, but that is an implementation
>> detail.
>>
>> If anything it should be called tst_cgroup_group, but I don't like the
>> repetition. :-p
>>
>
> Personally, I think tst_cgroup_node may be better since we have described
> a tree for cgroup.  root, node, and leaves(files) should be more vivid.
>

OK

>
>
>>> +
>> >> +    /* In general we avoid having sprintfs everywhere and use
>> >> +     * openat, linkat, etc.
>> >> +     */
>> >> +    int dir;
>> >
>> > Can we name this dir_fd so it's obvious what it is?
>>
>
> +1
> I stand by Cyril at this point.
>
>
>>> +/* Lookup tree for item names. */
>> >> +typedef struct cgroup_item items_t[];
>> >> +static items_t items = {
>> >> +    [0] = { "cgroup", .inner = (items_t){
>> >> +                    { "cgroup.procs", "tasks" },
>> >> +                    { "cgroup.subtree_control" },
>> >> +                    { "cgroup.clone_children", "clone_children" },
>> >> +                    { NULL }
>> >>              }
>> >> -    }
>> >> -    SAFE_FCLOSE(file);
>> >> +    },
>> >> +    [TST_CGROUP_MEMORY] = { "memory", .inner = (items_t){
>> >> +                    { "memory.current", "memory.usage_in_bytes" },
>> >> +                    { "memory.max", "memory.limit_in_bytes" },
>> >> +                    { "memory.swappiness", "memory.swappiness" },
>> >> +                    { "memory.swap.current",
>> "memory.memsw.usage_in_bytes" },
>> >> +                    { "memory.swap.max", "memory.memsw.limit_in_bytes"
>> },
>> >> +                    { "memory.kmem.usage_in_bytes",
>> "memory.kmem.usage_in_bytes" },
>> >> +                    { "memory.kmem.limit_in_bytes",
>> "memory.kmem.usage_in_bytes" },
>> >> +                    { NULL }
>> >> +            },
>> >> +      .css_indx = TST_CGROUP_MEMORY
>> >> +    },
>> >> +    [TST_CGROUP_CPUSET] = { "cpuset", .inner = (items_t){
>> >> +                    { "cpuset.cpus", "cpuset.cpus" },
>> >> +                    { "cpuset.mems", "cpuset.mems" },
>> >> +                    { "cpuset.memory_migrate", "cpuset.memory_migrate"
>> },
>> >> +                    { NULL }
>> >> +            },
>> >> +      .css_indx = TST_CGROUP_CPUSET
>> >> +    },
>> >> +    { NULL }
>> >> +};
>> >
>> > Item is a very generic word, this is a list of known knobs and map
>> > between v1 and v2. So maybe cgroup_knob_map or just cgroup_knobs ?
>>
>> I suppose that cgroup_item can be seperated into just two structs now
>> that I removed controller sub items like "memory.swap". This might help
>> solve the missing initializer warnings as well.
>
>
> To separate into two structs sounds good, the 'cgroup_item' contains both
> trunk node and controller files make things mess up.
>
>
>> I would not describe "memory.current" as a knob. It is a read only file
>> and I think of knobs as something you can write to. So I would prefer
>> cgroup_file and cgroup_subsys.
>
>
> +1
> cgroup_file and cgroup_subsys(or cgroup_controller) all very nice.

I will try cgroup_file and cgroup_ctrl.

-- 
Thank you,
Richard.