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, 10 insertions, 9 deletions

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 41631512ae97..f3e7da981610 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1090,6 +1090,7 @@ static void process_info(struct hv_dynmem_device *dm, struct dm_info_msg *msg)
 static unsigned long compute_balloon_floor(void)
 {
 	unsigned long min_pages;
+	unsigned long nr_pages = totalram_pages;
 #define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
 	/* Simple continuous piecewiese linear function:
 	 *  max MiB -> min MiB  gradient
@@ -1102,16 +1103,16 @@ static unsigned long compute_balloon_floor(void)
 	 *    8192       744    (1/16)
 	 *   32768      1512	(1/32)
 	 */
-	if (totalram_pages < MB2PAGES(128))
-		min_pages = MB2PAGES(8) + (totalram_pages >> 1);
-	else if (totalram_pages < MB2PAGES(512))
-		min_pages = MB2PAGES(40) + (totalram_pages >> 2);
-	else if (totalram_pages < MB2PAGES(2048))
-		min_pages = MB2PAGES(104) + (totalram_pages >> 3);
-	else if (totalram_pages < MB2PAGES(8192))
-		min_pages = MB2PAGES(232) + (totalram_pages >> 4);
+	if (nr_pages < MB2PAGES(128))
+		min_pages = MB2PAGES(8) + (nr_pages >> 1);
+	else if (nr_pages < MB2PAGES(512))
+		min_pages = MB2PAGES(40) + (nr_pages >> 2);
+	else if (nr_pages < MB2PAGES(2048))
+		min_pages = MB2PAGES(104) + (nr_pages >> 3);
+	else if (nr_pages < MB2PAGES(8192))
+		min_pages = MB2PAGES(232) + (nr_pages >> 4);
 	else
-		min_pages = MB2PAGES(488) + (totalram_pages >> 5);
+		min_pages = MB2PAGES(488) + (nr_pages >> 5);
 #undef MB2PAGES
 	return min_pages;
 }