mm: reference totalram_pages and managed_pages once per function

Patch series "mm: convert totalram_pages, totalhigh_pages and managed
pages to atomic", v5.

This series converts totalram_pages, totalhigh_pages and
zone->managed_pages to atomic variables.

totalram_pages, zone->managed_pages and totalhigh_pages updates are
protected by managed_page_count_lock, but readers never care about it.
Convert these variables to atomic to avoid readers potentially seeing a
store tear.

Main motivation was that managed_page_count_lock handling was complicating
things.  It was discussed in length here,
https://lore.kernel.org/patchwork/patch/995739/#1181785 It seemes better
to remove the lock and convert variables to atomic.  With the change,
preventing poteintial store-to-read tearing comes as a bonus.

This patch (of 4):

This is in preparation to a later patch which converts totalram_pages and
zone->managed_pages to atomic variables.  Please note that re-reading the
value might lead to a different value and as such it could lead to
unexpected behavior.  There are no known bugs as a result of the current
code but it is better to prevent from them in principle.

Link: http://lkml.kernel.org/r/1542090790-21750-2-git-send-email-arunks@codeaurora.org
Signed-off-by: Arun KS <arunks@codeaurora.org>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 2cc5fbb1b29e..ff727ff61b5b 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1131,6 +1131,7 @@ EXPORT_SYMBOL_GPL(dccp_debug);
 static int __init dccp_init(void)
 {
 	unsigned long goal;
+	unsigned long nr_pages = totalram_pages;
 	int ehash_order, bhash_order, i;
 	int rc;
 
@@ -1157,10 +1158,10 @@ static int __init dccp_init(void)
 	 *
 	 * The methodology is similar to that of the buffer cache.
 	 */
-	if (totalram_pages >= (128 * 1024))
-		goal = totalram_pages >> (21 - PAGE_SHIFT);
+	if (nr_pages >= (128 * 1024))
+		goal = nr_pages >> (21 - PAGE_SHIFT);
 	else
-		goal = totalram_pages >> (23 - PAGE_SHIFT);
+		goal = nr_pages >> (23 - PAGE_SHIFT);
 
 	if (thash_entries)
 		goal = (thash_entries *