Re: + memory-hotplug-fix-kswapd-looping-forever-problem-fix-fix.patch added to -mm tree

[Minchan Kim <minchan@kernel.org>]

On Fri, Jul 20, 2012 at 02:36:41PM -0700, Tejun Heo wrote:
> Hello, Andrew.
> 
> On Fri, Jul 20, 2012 at 02:22:13PM -0700, Andrew Morton wrote:
> > My point is that having to ensure that each arch zeroes out this
> > structure is difficult/costly/unreliable/fragile.  It would be better
> > if we can reliably clear it at some well-known place in core MM.
> > 
> > That might mean that the memory gets cleared twice on some
> > architectures, but I doubt if that matters - it's a once-off thing.
> 
> Clearing twice isn't the problem here.  The problem is the risk of
> zapping fields which are already in use.  That would be way more
> unexpected and difficult to track down than garbage value in whatever
> field.

I would like to know what fields you are concerning because most of field
in pg_data_t are generic except bdata so they would be initialized
by free_area_init_node. So IMHO, reset pg_data_t except bdata would be
no problem and clean approach. If some arch needs some fields in pg_data_t
, we have to declare new variable struct arch_data in pg_data_t and
generic functions doesn't need to touch them.
Of course, we can skip reset of that structure, too.

Please let me know it if I am missing something.

-- 
Kind regards,
Minchan Kim

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