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

[Minchan Kim <minchan@kernel.org>]

On Wed, Jul 18, 2012 at 02:38:10PM -0700, Andrew Morton wrote:
> On Wed, 18 Jul 2012 10:22:00 +0900
> Minchan Kim <minchan@kernel.org> wrote:
> 
> > > 
> > > Is this really necessary?  Does the zone start out all-zeroes?  If not, can we
> > > make it do so?
> > 
> > Good point.
> > It can remove zap_zone_vm_stats and zone->flags = 0, too.
> > More important thing is that we could remove adding code to initialize
> > zero whenever we add new field to zone. So I look at the code.
> > 
> > In summary, IMHO, all is already initialie zero out but we need double
> > check in mips.
> > 
> 
> Well, this is hardly a performance-critical path.  So rather than
> groveling around ensuring that each and every architectures does the
> right thing, would it not be better to put a single memset() into core
> MM if there is an appropriate place?

I think most good place is free_area_init_node but at a glance,
bootmem_data is set up eariler than free_area_init_node so shouldn't we
keep that pointer still?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 32985dd..1e7ca80 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4366,9 +4366,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
        int ret;
 
        pgdat_resize_init(pgdat);
-       pgdat->nr_zones = 0;
        init_waitqueue_head(&pgdat->kswapd_wait);
-       pgdat->kswapd_max_order = 0;
        pgdat_page_cgroup_init(pgdat);
 
        for (j = 0; j < MAX_NR_ZONES; j++) {
@@ -4429,11 +4427,6 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
 
                zone_pcp_init(zone);
                lruvec_init(&zone->lruvec, zone);
-               zap_zone_vm_stats(zone);
-               zone->flags = 0;
-#ifdef CONFIG_MEMORY_ISOLATION
-               zone->nr_pageblock_isolate = 0;
-#endif
                if (!size)
                        continue;
 
@@ -4495,7 +4488,15 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
                unsigned long node_start_pfn, unsigned long *zholes_size)
 {
        pg_data_t *pgdat = NODE_DATA(nid);
-
+       /* We guarantees pg_data_t starts out all-zeroes except bdata */
+#ifndef CONFIG_NO_BOOTMEM
+       struct bootmem_data *bdata;
+       bdata = pgdat->bdata;
+#endif
+       memset(pgdat, 0, sizeof(pg_data_t));
+#ifndef CONFIG_NO_BOOTMEM
+       pgdat->bdata = bdata;
+#endif
        pgdat->node_id = nid;
        pgdat->node_start_pfn = node_start_pfn;
        calculate_node_totalpages(pgdat, zones_size, zholes_size);

> 
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-- 
Kind regards,
Minchan Kim

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