[Xen-devel] [PATCH RFC] mm: fix regression with deferred struct page init

[Juergen Gross <jgross@xxxxxxxx>]

Commit 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time
instead of doing larger sections") is causing a regression on some
systems when the kernel is booted as Xen dom0.

The system will just hang in early boot.

Reason is an endless loop in get_page_from_freelist() in case the first
zone looked at has no free memory. deferred_grow_zone() is always
returning true due to the following code snipplet:

  /* If the zone is empty somebody else may have cleared out the zone */
  if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
                                           first_deferred_pfn)) {
          pgdat->first_deferred_pfn = ULONG_MAX;
          pgdat_resize_unlock(pgdat, &flags);
          return true;
  }

This in turn results in the loop as get_page_from_freelist() is
assuming forward progress can be made by doing some more struct page
initialization.

Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time instead 
of doing larger sections")
---
This patch makes my system boot again as Xen dom0, but I'm not really
sure it is the correct way to do it, hence the RFC.
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8abe0af..6ee754b5cd92 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1826,7 +1826,7 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
                                                 first_deferred_pfn)) {
                pgdat->first_deferred_pfn = ULONG_MAX;
                pgdat_resize_unlock(pgdat, &flags);
-               return true;
+               return false;
        }
 
        /*
-- 
2.16.4


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