Re: [PATCH] hugetlb_cgroup: explicitly init the early_init field

Re: [PATCH] hugetlb_cgroup: explicitly init the early_init field

[Hillf Danton]

On Tue, Apr 22, 2014 at 1:30 PM, Jianyu Zhan <nasa4836-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> For a cgroup subsystem who should init early, then it should carefully
> take care of the implementation of css_alloc, because it will be called
> before mm_init() setup the world.
>
> Luckily we don't, and we better explicitly assign the early_init field
> to 0, for document reason.
>
But other fields still missed, if any. Fair?

> Signed-off-by: Jianyu Zhan <nasa4836-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  mm/hugetlb_cgroup.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> index 595d7fd..b5368f8 100644
> --- a/mm/hugetlb_cgroup.c
> +++ b/mm/hugetlb_cgroup.c
> @@ -405,4 +405,5 @@ struct cgroup_subsys hugetlb_cgrp_subsys = {
>         .css_alloc      = hugetlb_cgroup_css_alloc,
>         .css_offline    = hugetlb_cgroup_css_offline,
>         .css_free       = hugetlb_cgroup_css_free,
> +       .early_init     = 0,
>  };
> --
> 2.0.0-rc0
>
> --
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Re: [PATCH] hugetlb_cgroup: explicitly init the early_init field

[Jianyu Zhan]

Hi, hillf,

On Tue, Apr 22, 2014 at 2:47 PM, Hillf Danton <dhillf-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> But other fields still missed, if any. Fair?

yep, it is not fair.

Sure for this global variable struct, if not initailized, its all
fields will be initialized
to 0 or null(depending on its type).  The point here is no to deprive
the rights of
compiler/linker of doing this initialization, it is mainly for
documentation reason.
Actually this field's value would affect how ->css_alloc should implemented.

Concretely, if early_init is nonzero, then ->css_alloc *must not* call kzalloc,
because in cgroup implementation, ->css_alloc will be called earlier before
mm_init().

I don't think that the value of one field(early_init) has a so subtle
restrition on the
another field(css_alloc) is a good thing, but since it is there,
docment it should
be needed.


Thanks,
Jianyu Zhan

Re: [PATCH] hugetlb_cgroup: explicitly init the early_init field

[Li Zefan]

On 2014/4/22 15:01, Jianyu Zhan wrote:
> Hi, hillf,
> 
> On Tue, Apr 22, 2014 at 2:47 PM, Hillf Danton <dhillf-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> But other fields still missed, if any. Fair?
> 
> yep, it is not fair.
> 
> Sure for this global variable struct, if not initailized, its all
> fields will be initialized
> to 0 or null(depending on its type).  The point here is no to deprive
> the rights of
> compiler/linker of doing this initialization, it is mainly for
> documentation reason.
> Actually this field's value would affect how ->css_alloc should implemented.
> 
> Concretely, if early_init is nonzero, then ->css_alloc *must not* call kzalloc,
> because in cgroup implementation, ->css_alloc will be called earlier before
> mm_init().
> 
> I don't think that the value of one field(early_init) has a so subtle
> restrition on the
> another field(css_alloc) is a good thing, but since it is there,
> docment it should
> be needed.
> 

I don't see how things can be improved by initializing it to 0 explicitly,
if anything needs to be improved.

[PATCH] hugetlb_cgroup: explicitly init the early_init field

[Jianyu Zhan]

For a cgroup subsystem who should init early, then it should carefully
take care of the implementation of css_alloc, because it will be called
before mm_init() setup the world.

Luckily we don't, and we better explicitly assign the early_init field
to 0, for document reason.

Signed-off-by: Jianyu Zhan <nasa4836-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 mm/hugetlb_cgroup.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 595d7fd..b5368f8 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -405,4 +405,5 @@ struct cgroup_subsys hugetlb_cgrp_subsys = {
 	.css_alloc	= hugetlb_cgroup_css_alloc,
 	.css_offline	= hugetlb_cgroup_css_offline,
 	.css_free	= hugetlb_cgroup_css_free,
+	.early_init	= 0,
 };
-- 
2.0.0-rc0