Commit 3d6357de authored by Arun KS's avatar Arun KS Committed by Linus Torvalds
Browse files

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: default avatarArun KS <arunks@codeaurora.org>
Reviewed-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarPavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent fecd4a50

arch/um/kernel/mem.c

+1 −1
Original line number Diff line number Diff line
@@ -52,7 +52,7 @@ void __init mem_init(void) 
	/* 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

+3 −2
Original line number Diff line number Diff line
@@ -434,9 +434,10 @@ static ssize_t microcode_write(struct file *file, const char __user *buf, 
			       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

+10 −9
Original line number Diff line number Diff line
@@ -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;

}

fs/file_table.c

+4 −3
Original line number Diff line number Diff line
@@ -380,10 +380,11 @@ void __init files_init(void) 
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

+3 −2
Original line number Diff line number Diff line
@@ -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)

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