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 --- kernel/fork.c | 5 +++-- kernel/kexec_core.c | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) (limited to 'kernel') diff --git a/kernel/fork.c b/kernel/fork.c index e2a5156bc9c3..8617a326e9f5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -744,15 +744,16 @@ void __init __weak arch_task_cache_init(void) { } static void set_max_threads(unsigned int max_threads_suggested) { u64 threads; + unsigned long nr_pages = totalram_pages; /* * The number of threads shall be limited such that the thread * structures may only consume a small part of the available memory. */ - if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64) + if (fls64(nr_pages) + fls64(PAGE_SIZE) > 64) threads = MAX_THREADS; else - threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE, + threads = div64_u64((u64) nr_pages * (u64) PAGE_SIZE, (u64) THREAD_SIZE * 8UL); if (threads > max_threads_suggested) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 86ef06d3dbe3..7e967ca98d92 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -152,6 +152,7 @@ int sanity_check_segment_list(struct kimage *image) int i; unsigned long nr_segments = image->nr_segments; unsigned long total_pages = 0; + unsigned long nr_pages = totalram_pages; /* * Verify we have good destination addresses. The caller is @@ -217,13 +218,13 @@ int sanity_check_segment_list(struct kimage *image) * wasted allocating pages, which can cause a soft lockup. */ for (i = 0; i < nr_segments; i++) { - if (PAGE_COUNT(image->segment[i].memsz) > totalram_pages / 2) + if (PAGE_COUNT(image->segment[i].memsz) > nr_pages / 2) return -EINVAL; total_pages += PAGE_COUNT(image->segment[i].memsz); } - if (total_pages > totalram_pages / 2) + if (total_pages > nr_pages / 2) return -EINVAL; /* -- cgit v1.2.3