On Mon 26-06-17 11:58:22, Wei Yang wrote:
> In commit (9adb62a5df9c0fbef7) "mm/hotplug: correctly setup fallback
> zonelists when creating new pgdat" tries to build the correct zonelist for
> a new added node, while it is not necessary to rebuild it for already exist
> nodes.
>
> In build_zonelists(), it will iterate on nodes with memory. For a new added
> node, it will have memory until node_states_set_node() is called in
> online_pages().
>
> This patch will avoid to rebuild the zonelists for already exist nodes.
It is not very clear from the changelog why that actually matters. The
only effect I can see is that other zonelists on other online nodes will
not learn about the currently memory less node. This is a good think
because we do not pointlessly try to allocate from that node.
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 560eafe8234d..fc8181b44fd8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5200,15 +5200,17 @@ static int __build_all_zonelists(void *data)
> memset(node_load, 0, sizeof(node_load));
> #endif
>
> - if (self && !node_online(self->node_id)) {
> + /* This node is hotadded and no memory preset yet.
> + * So just build zonelists is fine, no need to touch other nodes.
> + */
This comment doesn't make much sense to me. What about
/*
* Do not rebuild zonelists on all online nodes if the current
* node is not online yet (it doesn't have any memory) and
* allocating from it is pointless. Still build zonelist for
* self because we need to handle memoryless nodes.
*/
> + if (self && !node_online(self->node_id))
> build_zonelists(self);
> - }
> -
> - for_each_online_node(nid) {
> - pg_data_t *pgdat = NODE_DATA(nid);
> + else
> + for_each_online_node(nid) {
> + pg_data_t *pgdat = NODE_DATA(nid);
>
> - build_zonelists(pgdat);
> - }
> + build_zonelists(pgdat);
> + }
>
> /*
> * Initialize the boot_pagesets that are going to be used
> --
> 2.11.0
>
> --
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--
Michal Hocko
SUSE Labs
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