On Wed, 19 Jan 2011 09:27:33 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> On Tue, 18 Jan 2011 15:28:44 -0800
> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Tue, 18 Jan 2011 12:18:11 +0100
> > Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >
> > > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> > > +{
> > > + int error;
> > > + struct mem_cgroup *memcg = NULL;
> >
> > I'm suspecting that the unneeded initialisation was added to suppress a
> > warning?
> >
> No.
> It's necessary for mem_cgroup_{prepare|end}_migration().
> mem_cgroup_prepare_migration() will return without doing anything in
> "if (mem_cgroup_disabled()" case(iow, "memcg" is not overwritten),
> but mem_cgroup_end_migration() depends on the value of "memcg" to decide
> whether prepare_migration has succeeded or not.
> This may not be a good implementation,
It's a *surprising* implementation, in the context of kernel
conventions. At least, it fooled me :)
Which makes it a not-good implementation, really. Also, it's
undocumented.
> but IMHO I'd like to to initialize
> valuable before using it in general.
mem_cgroup_prepare_migration() performs the initialisation! We do this
in many places - it's the basic "function with more than one return
value" mechanism.
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
