Messages in this thread Patch in this message | | | From | Cody P Schafer <> | Subject | [RFC PATCH v3 28/31] mm/page_alloc: in page_outside_zone_boundaries(), avoid premature decisions. | Date | Thu, 2 May 2013 17:01:00 -0700 |
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With some code that expands the zone boundaries, VM_BUG_ON(bad_range()) was being triggered.
Previously, page_outside_zone_boundaries() decided that once it detected a page outside the boundaries, it was certainly outside even if the seqlock indicated the data was invalid & needed to be reread. This methodology _almost_ works because zones are only ever grown. However, becase the zone span is stored as a start and a length, some expantions momentarily appear as shifts to the left (when the zone_start_pfn is assigned prior to zone_spanned_pages).
If we want to remove the seqlock around zone_start_pfn & zone spanned_pages, always writing the spanned_pages first, issuing a memory barrier, and then writing the new zone_start_pfn _may_ work. The concern there is that we could be seen as shrinking the span when zone_start_pfn is written (the entire span would shift to the left). As there will be no pages in the exsess span that actually belong to the zone being manipulated, I don't expect there to be issues.
Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com> --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 879ab9d..3695ca5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -239,12 +239,13 @@ bool oom_killer_disabled __read_mostly; #ifdef CONFIG_DEBUG_VM static int page_outside_zone_boundaries(struct zone *zone, struct page *page) { - int ret = 0; + int ret; unsigned seq; unsigned long pfn = page_to_pfn(page); unsigned long sp, start_pfn; do { + ret = 0; seq = zone_span_seqbegin(zone); start_pfn = zone->zone_start_pfn; sp = zone->spanned_pages; -- 1.8.2.2
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