linux-kernel - [PATCH RFC] mm: fix regression with deferred struct page init

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Message-Id: <20190620094015.21206-1-jgross@suse.com>
Date:   Thu, 20 Jun 2019 11:40:15 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: [PATCH RFC] mm: fix regression with deferred struct page init

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@...e.com>
---
 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