From: Mel Gorman <mgorman@xxxxxxx>
This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
===============
commit c78e93630d15b5f5774213aad9bdc9f52473a89b upstream.
It has been reported on very large machines that show_mem is taking almost
5 minutes to display information. This is a serious problem if there is
an OOM storm. The bulk of the cost is in show_mem doing a very expensive
PFN walk to give us the following information
Total RAM: Also available as totalram_pages
Highmem pages: Also available as totalhigh_pages
Reserved pages: Can be inferred from the zone structure
Shared pages: PFN walk required
Unshared pages: PFN walk required
Quick pages: Per-cpu walk required
Only the shared/unshared pages requires a full PFN walk but that
information is useless. It is also inaccurate as page pins of unshared
pages would be accounted for as shared. Even if the information was
accurate, I'm struggling to think how the shared/unshared information
could be useful for debugging OOM conditions. Maybe it was useful before
rmap existed when reclaiming shared pages was costly but it is less
relevant today.
The PFN walk could be optimised a bit but why bother as the information is
useless. This patch deletes the PFN walker and infers the total RAM,
highmem and reserved pages count from struct zone. It omits the
shared/unshared page usage on the grounds that it is useless. It also
corrects the reporting of HighMem as HighMem/MovableOnly as ZONE_MOVABLE
has similar problems to HighMem with respect to lowmem/highmem exhaustion.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
lib/show_mem.c | 39 +++++++++++----------------------------
1 file changed, 11 insertions(+), 28 deletions(-)
diff --git a/lib/show_mem.c b/lib/show_mem.c
index b7c72311ad0c..5847a4921b8e 100644
--- a/lib/show_mem.c
+++ b/lib/show_mem.c
@@ -12,8 +12,7 @@
void show_mem(unsigned int filter)
{
pg_data_t *pgdat;
- unsigned long total = 0, reserved = 0, shared = 0,
- nonshared = 0, highmem = 0;
+ unsigned long total = 0, reserved = 0, highmem = 0;
printk("Mem-Info:\n");
show_free_areas(filter);
@@ -22,43 +21,27 @@ void show_mem(unsigned int filter)
return;
for_each_online_pgdat(pgdat) {
- unsigned long i, flags;
+ unsigned long flags;
+ int zoneid;
pgdat_resize_lock(pgdat, &flags);
- for (i = 0; i < pgdat->node_spanned_pages; i++) {
- struct page *page;
- unsigned long pfn = pgdat->node_start_pfn + i;
-
- if (unlikely(!(i % MAX_ORDER_NR_PAGES)))
- touch_nmi_watchdog();
-
- if (!pfn_valid(pfn))
+ for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
+ struct zone *zone = &pgdat->node_zones[zoneid];
+ if (!populated_zone(zone))
continue;
- page = pfn_to_page(pfn);
-
- if (PageHighMem(page))
- highmem++;
+ total += zone->present_pages;
+ reserved = zone->present_pages - zone->managed_pages;
- if (PageReserved(page))
- reserved++;
- else if (page_count(page) == 1)
- nonshared++;
- else if (page_count(page) > 1)
- shared += page_count(page) - 1;
-
- total++;
+ if (is_highmem_idx(zoneid))
+ highmem += zone->present_pages;
}
pgdat_resize_unlock(pgdat, &flags);
}
printk("%lu pages RAM\n", total);
-#ifdef CONFIG_HIGHMEM
- printk("%lu pages HighMem\n", highmem);
-#endif
+ printk("%lu pages HighMem/MovableOnly\n", highmem);
printk("%lu pages reserved\n", reserved);
- printk("%lu pages shared\n", shared);
- printk("%lu pages non-shared\n", nonshared);
#ifdef CONFIG_QUICKLIST
printk("%lu pages in pagetable cache\n",
quicklist_total_size());
--
1.9.0
--
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