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>

4 files changed, 15 insertions, 11 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 *
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index e87c21e47efe..5eb990830348 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -2248,6 +2248,7 @@ static __always_inline unsigned int total_extension_size(void)
 
 int nf_conntrack_init_start(void)
 {
+	unsigned long nr_pages = totalram_pages;
 	int max_factor = 8;
 	int ret = -ENOMEM;
 	int i;
@@ -2267,11 +2268,11 @@ int nf_conntrack_init_start(void)
 		 * >= 4GB machines have 65536 buckets.
 		 */
 		nf_conntrack_htable_size
-			= (((totalram_pages << PAGE_SHIFT) / 16384)
+			= (((nr_pages << PAGE_SHIFT) / 16384)
 			   / sizeof(struct hlist_head));
-		if (totalram_pages > (4 * (1024 * 1024 * 1024 / PAGE_SIZE)))
+		if (nr_pages > (4 * (1024 * 1024 * 1024 / PAGE_SIZE)))
 			nf_conntrack_htable_size = 65536;
-		else if (totalram_pages > (1024 * 1024 * 1024 / PAGE_SIZE))
+		else if (nr_pages > (1024 * 1024 * 1024 / PAGE_SIZE))
 			nf_conntrack_htable_size = 16384;
 		if (nf_conntrack_htable_size < 32)
 			nf_conntrack_htable_size = 32;
diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 28e27a32d9b9..88b520ba2abc 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -274,14 +274,15 @@ static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
 	struct xt_hashlimit_htable *hinfo;
 	const struct seq_operations *ops;
 	unsigned int size, i;
+	unsigned long nr_pages = totalram_pages;
 	int ret;
 
 	if (cfg->size) {
 		size = cfg->size;
 	} else {
-		size = (totalram_pages << PAGE_SHIFT) / 16384 /
+		size = (nr_pages << PAGE_SHIFT) / 16384 /
 		       sizeof(struct hlist_head);
-		if (totalram_pages > 1024 * 1024 * 1024 / PAGE_SIZE)
+		if (nr_pages > 1024 * 1024 * 1024 / PAGE_SIZE)
 			size = 8192;
 		if (size < 16)
 			size = 16;
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index 9b277bd36d1a..a5b24182b3cc 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1368,6 +1368,7 @@ static __init int sctp_init(void)
 	int status = -EINVAL;
 	unsigned long goal;
 	unsigned long limit;
+	unsigned long nr_pages = totalram_pages;
 	int max_share;
 	int order;
 	int num_entries;
@@ -1426,10 +1427,10 @@ static __init int sctp_init(void)
 	 * The methodology is similar to that of the tcp hash tables.
 	 * Though not identical.  Start by getting a goal size
 	 */
-	if (totalram_pages >= (128 * 1024))
-		goal = totalram_pages >> (22 - PAGE_SHIFT);
+	if (nr_pages >= (128 * 1024))
+		goal = nr_pages >> (22 - PAGE_SHIFT);
 	else
-		goal = totalram_pages >> (24 - PAGE_SHIFT);
+		goal = nr_pages >> (24 - PAGE_SHIFT);
 
 	/* Then compute the page order for said goal */
 	order = get_order(goal);