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Subject[PATCH] mm: fix a regression with HIGHMEM introduced by changeset 7f1290f2f2a4d
Date
Changeset 7f1290f2f2 tries to fix a issue when calculating
zone->present_pages, but it causes a regression to 32bit systems with
HIGHMEM. With that changeset, function reset_zone_present_pages()
resets all zone->present_pages to zero, and fixup_zone_present_pages()
is called to recalculate zone->present_pages when boot allocator frees
core memory pages into buddy allocator. Because highmem pages are not
freed by bootmem allocator, all highmem zones' present_pages becomes
zero.

Actually there's no need to recalculate present_pages for highmem zone
because bootmem allocator never allocates pages from them. So fix the
regression by skipping highmem in function reset_zone_present_pages()
and fixup_zone_present_pages().

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
Reported-by: Maciej Rutecki <maciej.rutecki@gmail.com>
Tested-by: Maciej Rutecki <maciej.rutecki@gmail.com>
Cc: Chris Clayton <chris2553@googlemail.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org

---

Hi Maciej,
Thanks for reporting and bisecting. We have analyzed the regression
and worked out a patch for it. Could you please help to verify whether it
fix the regression?
Thanks!
Gerry

---
mm/page_alloc.c | 8 +++++---
1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b74de6..2311f15 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6108,7 +6108,8 @@ void reset_zone_present_pages(void)
for_each_node_state(nid, N_HIGH_MEMORY) {
for (i = 0; i < MAX_NR_ZONES; i++) {
z = NODE_DATA(nid)->node_zones + i;
- z->present_pages = 0;
+ if (!is_highmem(z))
+ z->present_pages = 0;
}
}
}
@@ -6123,10 +6124,11 @@ void fixup_zone_present_pages(int nid, unsigned long start_pfn,

for (i = 0; i < MAX_NR_ZONES; i++) {
z = NODE_DATA(nid)->node_zones + i;
+ if (is_highmem(z))
+ continue;
+
zone_start_pfn = z->zone_start_pfn;
zone_end_pfn = zone_start_pfn + z->spanned_pages;
-
- /* if the two regions intersect */
if (!(zone_start_pfn >= end_pfn || zone_end_pfn <= start_pfn))
z->present_pages += min(end_pfn, zone_end_pfn) -
max(start_pfn, zone_start_pfn);
--
1.7.1



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