Re: + hugetlb-fix-section-mismatch-warning-in-hugetlbc.patch added to -mm tree

Re: + hugetlb-fix-section-mismatch-warning-in-hugetlbc.patch added to -mm tree

[Randy Dunlap]

On Thu, 07 Jan 2010 14:18:25 -0800 akpm@linux-foundation.org wrote:

> 
> The patch titled
>      hugetlb: fix section mismatch warning in hugetlb.c
> has been added to the -mm tree.  Its filename is
>      hugetlb-fix-section-mismatch-warning-in-hugetlbc.patch
> 
> 
> ------------------------------------------------------
> Subject: hugetlb: fix section mismatch warning in hugetlb.c
> From: Rakib Mullick <rakib.mullick@gmail.com>
> 
> Since hugetlb_sysfs_add_hstate()'s caller is __init and it isn't
> referencing from any other function, we can do this.

Hi,

I looked at this section mismatch warning too.
Maybe I'm reading too much into it (so I have cc-ed linux-mm),
but it looks like hugetlbfs supports callbacks for node
hotplug & unplug:

in hugetlb_register_all_nodes():

	/*
	 * Let the node sysdev driver know we're here so it can
	 * [un]register hstate attributes on node hotplug.
	 */
	register_hugetlbfs_with_node(hugetlb_register_node,
				     hugetlb_unregister_node);

If so, then hugetlb_register_node() could be called at any time
(like after system init), and it would then call
hugetlb_sysfs_add_hstate(), which would be bad.

Am I misunderstanding the hotplug callbacks?
or can you explain just a bit better, please?
Thanks.


> Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  mm/hugetlb.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff -puN mm/hugetlb.c~hugetlb-fix-section-mismatch-warning-in-hugetlbc mm/hugetlb.c
> --- a/mm/hugetlb.c~hugetlb-fix-section-mismatch-warning-in-hugetlbc
> +++ a/mm/hugetlb.c
> @@ -1650,7 +1650,7 @@ static void hugetlb_unregister_all_nodes
>   * Register hstate attributes for a single node sysdev.
>   * No-op if attributes already registered.
>   */
> -void hugetlb_register_node(struct node *node)
> +void __init hugetlb_register_node(struct node *node)
>  {
>  	struct hstate *h;
>  	struct node_hstate *nhs = &node_hstates[node->sysdev.id];
> @@ -1683,7 +1683,7 @@ void hugetlb_register_node(struct node *
>   * sysdevs of nodes that have memory.  All on-line nodes should have
>   * registered their associated sysdev by this time.
>   */
> -static void hugetlb_register_all_nodes(void)
> +static void __init hugetlb_register_all_nodes(void)
>  {
>  	int nid;
>  
> @@ -1712,7 +1712,7 @@ static struct hstate *kobj_to_node_hstat
>  
>  static void hugetlb_unregister_all_nodes(void) { }
>  
> -static void hugetlb_register_all_nodes(void) { }
> +static void __init hugetlb_register_all_nodes(void) { }
>  
>  #endif
>  
> _


---
~Randy

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Re: + hugetlb-fix-section-mismatch-warning-in-hugetlbc.patch added to -mm tree

[Rakib Mullick]

On 1/8/10, Randy Dunlap <randy.dunlap@oracle.com> wrote:

Hi,
>
> Hi,
>
>  If so, then hugetlb_register_node() could be called at any time
>  (like after system init), and it would then call
>  hugetlb_sysfs_add_hstate(), which would be bad.
>
But - hugetlb_register_node is only called from hugetlb_register_all_nodes.
The call sequence is :
                    hugetlb_init   --------------->  was __init
                         \-> hugetlb_register_all_nodes  ----> we make it __init
                                          \-> hugetlb_register_node
---> we make it __init
                                                 \->
hugetlb_sysfs_add_hstate -> this was __init

Above all happens in __init context. So - hugetlb_register_node is
called only at
system init. But I don't think __init is used for hotplug support, for
proper hotplug
support we might use __meminit.

And register_hugetlbfs_with_node is called from hugetlb_un/register_node.
But hugetlb_unregister_node doesn't use callback function. It's not referencing
hugetlb_sysfs_add_hstate(). So - it's safe. Unless I'm not missing
anything, too.

thanks,

>  Thanks.
> ---
>
> ~Randy
>

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Re: + hugetlb-fix-section-mismatch-warning-in-hugetlbc.patch added to -mm tree

[Lee Schermerhorn]

On Fri, 2010-01-08 at 12:34 +0600, Rakib Mullick wrote:
> On 1/8/10, Randy Dunlap <randy.dunlap@oracle.com> wrote:
> 
> Hi,
> >
> > Hi,
> >
> >  If so, then hugetlb_register_node() could be called at any time
> >  (like after system init), and it would then call
> >  hugetlb_sysfs_add_hstate(), which would be bad.
> >
> But - hugetlb_register_node is only called from hugetlb_register_all_nodes.

No, hugetlb_register_node() is also called from the similarly named
function in drivers/base/node.c.   mm/hugetlb.c registers its version of
"hugetlb_register_node()" at start up for use at node hotplug.  See
register_hugetlbfs_with_node() in node.c and its use in hugetlb.c.

We had to do it this way because node.c is part of the base kernel and
hugetlb support can be built as a module.  All sysfs node kobjs have
been registered by the time hugetlb inits, so hugetlb registers the
nodes' hstate attributes when it initializes.  However, when a node is
hotplugged later, the node driver calls into hugetlb to register the
attributes.

So, we need to keep mm/hugetlb.c:hugetlb_register_node() around during
run time when mem/node hot-plug is supported.

Lee


> The call sequence is :
>                     hugetlb_init   --------------->  was __init
>                          \-> hugetlb_register_all_nodes  ----> we make it __init
>                                           \-> hugetlb_register_node
> ---> we make it __init
>                                                  \->
> hugetlb_sysfs_add_hstate -> this was __init
> 
> Above all happens in __init context. So - hugetlb_register_node is
> called only at
> system init. But I don't think __init is used for hotplug support, for
> proper hotplug
> support we might use __meminit.
> 
> And register_hugetlbfs_with_node is called from hugetlb_un/register_node.
> But hugetlb_unregister_node doesn't use callback function. It's not referencing
> hugetlb_sysfs_add_hstate(). So - it's safe. Unless I'm not missing
> anything, too.
> 
> thanks,
> 
> >  Thanks.
> > ---
> >
> > ~Randy
> >
> 
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