From 3d6357de8aa09e1966770dc1171c72679946464f Mon Sep 17 00:00:00 2001 From: Arun KS Date: Fri, 28 Dec 2018 00:34:20 -0800 Subject: 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 Reviewed-by: Konstantin Khlebnikov Reviewed-by: David Hildenbrand Acked-by: Michal Hocko Acked-by: Vlastimil Babka Reviewed-by: Pavel Tatashin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/hv/hv_balloon.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) (limited to 'drivers/hv') 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; } -- cgit v1.2.3