[PATCH] fix page_reset_bad_cgroup

[PATCH] fix page_reset_bad_cgroup

[KAMEZAWA Hiroyuki]

page->page_cgroup is unsigned long. Should be cleared by 0UL.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


Index: linux-2.6.25/include/linux/memcontrol.h
===================================================================
--- linux-2.6.25.orig/include/linux/memcontrol.h
+++ linux-2.6.25/include/linux/memcontrol.h
@@ -30,7 +30,7 @@ struct mm_struct;
 extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
 extern void mm_free_cgroup(struct mm_struct *mm);
 
-#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)
+#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0UL)
 
 extern struct page_cgroup *page_get_page_cgroup(struct page *page);
 extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,

Re: [PATCH] fix page_reset_bad_cgroup

[Andrew Morton]

On Fri, 18 Apr 2008 12:10:46 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> page->page_cgroup is unsigned long. Should be cleared by 0UL.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> 
> Index: linux-2.6.25/include/linux/memcontrol.h
> ===================================================================
> --- linux-2.6.25.orig/include/linux/memcontrol.h
> +++ linux-2.6.25/include/linux/memcontrol.h
> @@ -30,7 +30,7 @@ struct mm_struct;
>  extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
>  extern void mm_free_cgroup(struct mm_struct *mm);
>  
> -#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)
> +#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0UL)

That's pretty cosmetic.

In fact it could be argued that we shouldn't do this.  "0" is zero
regardless of the type of the LHS.  So if we later change page_cgroup to
u32 or u16 or `struct superblock *', the old page_reset_bad_cgroup() will
happily continue to work.  There's no need to make this code aware of
page_cgroup's type, to this extent?

Re: [PATCH] fix page_reset_bad_cgroup

[KAMEZAWA Hiroyuki]

On Thu, 17 Apr 2008 20:22:21 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 18 Apr 2008 12:10:46 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > page->page_cgroup is unsigned long. Should be cleared by 0UL.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > 
> > 
> > Index: linux-2.6.25/include/linux/memcontrol.h
> > ===================================================================
> > --- linux-2.6.25.orig/include/linux/memcontrol.h
> > +++ linux-2.6.25/include/linux/memcontrol.h
> > @@ -30,7 +30,7 @@ struct mm_struct;
> >  extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
> >  extern void mm_free_cgroup(struct mm_struct *mm);
> >  
> > -#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)
> > +#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0UL)
> 
> That's pretty cosmetic.
> 
> In fact it could be argued that we shouldn't do this.  "0" is zero
> regardless of the type of the LHS.  So if we later change page_cgroup to
> u32 or u16 or `struct superblock *', the old page_reset_bad_cgroup() will
> happily continue to work.  There's no need to make this code aware of
> page_cgroup's type, to this extent?
>
Ah, sorry. I was confused...please ignore.
(I debugged an user program which clear a pointer with 0, yesterday..)

-Kame