Re: [PATCH -mm] mm: Fix memory hotplug + sparsemem build.

Andy Whitcroft
2007-09-11T09:15:16Z

On Tue, Sep 11, 2007 at 05:18:01PM +0900, Yasunori Goto wrote:
> > if (onlined_pages)
> > - node_set_state(zone->node, N_HIGH_MEMORY);
> > + node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
> >
> > setup_per_zone_pages_min();
>
> Thanks Paul-san.
>
> I also have another issue around here.
> (Kswapd doesn't run on memory less node now. It should run when
> the node has memory.)
>
> I would like to merge them like following if you don't mind.
>
>
> Bye.
>
> ---
>
> Fix kswapd doesn't run when memory is added on memory-less-node.
> Fix compile error of zone->node when CONFIG_NUMA is off.
>
> Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
> Signed-off-by: Paul Mundt <lethal@linux-sh.org>
>
>
> ---
> mm/memory_hotplug.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> Index: current/mm/memory_hotplug.c
> ===================================================================
> --- current.orig/mm/memory_hotplug.c 2007-09-07 18:08:07.000000000 +0900
> +++ current/mm/memory_hotplug.c 2007-09-11 17:29:19.000000000 +0900
> @@ -211,10 +211,12 @@ int online_pages(unsigned long pfn, unsi
> online_pages_range);
> zone->present_pages += onlined_pages;
> zone->zone_pgdat->node_present_pages += onlined_pages;
> - if (onlined_pages)
> - node_set_state(zone->node, N_HIGH_MEMORY);
>
> setup_per_zone_pages_min();
> + if (onlined_pages){

Nit, needs a space there before the '{'.

> + kswapd_run(zone_to_nid(zone));
> + node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
> + }
>
> if (need_zonelists_rebuild)
> build_all_zonelists();
> @@ -269,9 +271,6 @@ int add_memory(int nid, u64 start, u64 s
> if (!pgdat)
> return -ENOMEM;
> new_pgdat = 1;
> - ret = kswapd_run(nid);
> - if (ret)
> - goto error;
> }
>
> /* call arch's memory hotadd */

The problem as I see it is that when we boot the system we start a
kswapd on all nodes with memory. If the hot-add adds memory to a
pre-existing node with no memory we will not start one and we end up
with a node with memory and no kswapd. Bad.

As kswapd_run is a no-op when a kswapd already exists this seems a safe
way to fix that. Paul's ->zone conversion is obviously correct also.

Acked-by: Andy Whitcroft <apw@shadowen.org>

-apw