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From:   Oscar Salvador <osalvador@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Pavel Tatashin <pasha.tatashin@soleen.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Oscar Salvador <osalvador@suse.de>
Subject: [PATCH v2 1/3] mm,page_alloc: Use {get,put}_online_mems() to get stable zone's values
Date:   Wed,  2 Jun 2021 11:14:55 +0200
Message-Id: <20210602091457.17772-2-osalvador@suse.de>
In-Reply-To: <20210602091457.17772-1-osalvador@suse.de>
References: <20210602091457.17772-1-osalvador@suse.de>
Precedence: bulk

Currently, page_outside_zone_boundaries() takes zone's span_seqlock
when reading zone_start_pfn and spanned_pages so those values are
stable vs memory hotplug operations.
move_pfn_range_to_zone() and remove_pfn_range_from_zone(), which are
the functions that can change zone's values are serialized by
mem_hotplug_lock by mem_hotplug_{begin,done}, so we can just use
{get,put}_online_mems() on the readers.

This will allow us to completely kill span_seqlock lock as no users
will remain after this series.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 mm/page_alloc.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index aaa1655cf682..296cb00802b4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -582,17 +582,15 @@ void set_pageblock_migratetype(struct page *page, int migratetype)
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {
 	int ret = 0;
-	unsigned seq;
 	unsigned long pfn = page_to_pfn(page);
 	unsigned long sp, start_pfn;
 
-	do {
-		seq = zone_span_seqbegin(zone);
-		start_pfn = zone->zone_start_pfn;
-		sp = zone->spanned_pages;
-		if (!zone_spans_pfn(zone, pfn))
-			ret = 1;
-	} while (zone_span_seqretry(zone, seq));
+	get_online_mems();
+	start_pfn = zone->zone_start_pfn;
+	sp = zone->spanned_pages;
+	if (!zone_spans_pfn(zone, pfn))
+		ret = 1;
+	put_online_mems();
 
 	if (ret)
 		pr_err("page 0x%lx outside node %d zone %s [ 0x%lx - 0x%lx ]\n",
-- 
2.16.3