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/[e-mail]
Signed-off-by: Arun KS <[e-mail]>
Reviewed-by: Konstantin Khlebnikov <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Reviewed-by: Pavel Tatashin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/kernel/mem.c

···
 	/* this will put all low memory onto the freelists */
 	memblock_free_all();
 	max_low_pfn = totalram_pages;
-	max_pfn = totalram_pages;
+	max_pfn = max_low_pfn;
 	mem_init_print_info(NULL);
 	kmalloc_ok = 1;
 }

arch/x86/kernel/cpu/microcode/core.c

···
 			       size_t len, loff_t *ppos)
 {
 	ssize_t ret = -EINVAL;
+	unsigned long nr_pages = totalram_pages;
 
-	if ((len >> PAGE_SHIFT) > totalram_pages) {
-		pr_err("too much data (max %ld pages)\n", totalram_pages);
+	if ((len >> PAGE_SHIFT) > nr_pages) {
+		pr_err("too much data (max %ld pages)\n", nr_pages);
 		return ret;
 	}
 

drivers/hv/hv_balloon.c

···
 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
···
 	 *    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;
 }

fs/file_table.c

···
 void __init files_maxfiles_init(void)
 {
 	unsigned long n;
-	unsigned long memreserve = (totalram_pages - nr_free_pages()) * 3/2;
+	unsigned long nr_pages = totalram_pages;
+	unsigned long memreserve = (nr_pages - nr_free_pages()) * 3/2;
 
-	memreserve = min(memreserve, totalram_pages - 1);
-	n = ((totalram_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
+	memreserve = min(memreserve, nr_pages - 1);
+	n = ((nr_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
 
 	files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 }

kernel/fork.c

···
 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)

kernel/kexec_core.c

···
 	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
···
 	 * 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;
 
 	/*

mm/page_alloc.c

···
 		for (i = 0; i < MAX_NR_ZONES; i++) {
 			struct zone *zone = pgdat->node_zones + i;
 			long max = 0;
+			unsigned long managed_pages = zone->managed_pages;
 
 			/* Find valid and maximum lowmem_reserve in the zone */
 			for (j = i; j < MAX_NR_ZONES; j++) {
···
 			/* we treat the high watermark as reserved pages. */
 			max += high_wmark_pages(zone);
 
-			if (max > zone->managed_pages)
-				max = zone->managed_pages;
+			if (max > managed_pages)
+				max = managed_pages;
 
 			pgdat->totalreserve_pages += max;
 

mm/shmem.c

···
 
 static unsigned long shmem_default_max_inodes(void)
 {
-	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
+	unsigned long nr_pages = totalram_pages;
+	return min(nr_pages - totalhigh_pages, nr_pages / 2);
 }
 #endif
 

net/dccp/proto.c

···
 static int __init dccp_init(void)
 {
 	unsigned long goal;
+	unsigned long nr_pages = totalram_pages;
 	int ehash_order, bhash_order, i;
 	int rc;
 
···
 	 *
 	 * 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 *

net/netfilter/nf_conntrack_core.c

···
 
 int nf_conntrack_init_start(void)
 {
+	unsigned long nr_pages = totalram_pages;
 	int max_factor = 8;
 	int ret = -ENOMEM;
 	int i;
···
 		 * >= 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;

net/netfilter/xt_hashlimit.c

···
 	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;

net/sctp/protocol.c

···
 	int status = -EINVAL;
 	unsigned long goal;
 	unsigned long limit;
+	unsigned long nr_pages = totalram_pages;
 	int max_share;
 	int order;
 	int num_entries;
···
 	 * 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);