Re: [PATCH v1 4/4] mm: Remove managed_page_count spinlock

[for some reason I have dropped the rest of the cc list. Restored]

On Tue 06-11-18 15:17:32, Michal Hocko wrote:

On Fri 26-10-18 16:31:02, Arun KS wrote:

quoted

Now totalram_pages and managed_pages are atomic varibles. No need
of managed_page_count spinlock.

Yes this is the real improvement. The lock had really a weak consistency
guarantee. It hasn't been used for anything but the update but no reader
actually cares about all the values being updated to be in sync. I
haven't really done an excavation work to see whether it used to be used
in other contexts in the past but it simply doesn't have any meaning
anymore.

quoted

Signed-off-by: Arun KS <redacted>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks for getting through all the hassles to reach to this end point.

quoted

---
 include/linux/mmzone.h | 6 ------
 mm/page_alloc.c        | 5 -----
 2 files changed, 11 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 597b0c7..aa960f6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -428,12 +428,6 @@ struct zone {
 	 * Write access to present_pages at runtime should be protected by
 	 * mem_hotplug_begin/end(). Any reader who can't tolerant drift of
 	 * present_pages should get_online_mems() to get a stable value.
-	 *
-	 * Read access to managed_pages should be safe because it's unsigned
-	 * long. Write access to zone->managed_pages and totalram_pages are
-	 * protected by managed_page_count_lock at runtime. Idealy only
-	 * adjust_managed_page_count() should be used instead of directly
-	 * touching zone->managed_pages and totalram_pages.
 	 */
 	atomic_long_t		managed_pages;
 	unsigned long		spanned_pages;

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index af832de..e29e78f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -122,9 +122,6 @@
 };
 EXPORT_SYMBOL(node_states);
 
-/* Protect totalram_pages and zone->managed_pages */
-static DEFINE_SPINLOCK(managed_page_count_lock);
-
 atomic_long_t _totalram_pages __read_mostly;
 unsigned long totalreserve_pages __read_mostly;
 unsigned long totalcma_pages __read_mostly;

@@ -7062,14 +7059,12 @@ static int __init cmdline_parse_movablecore(char *p)
 
 void adjust_managed_page_count(struct page *page, long count)
 {
-	spin_lock(&managed_page_count_lock);
 	atomic_long_add(count, &page_zone(page)->managed_pages);
 	totalram_pages_add(count);
 #ifdef CONFIG_HIGHMEM
 	if (PageHighMem(page))
 		totalhigh_pages_add(count);
 #endif
-	spin_unlock(&managed_page_count_lock);
 }
 EXPORT_SYMBOL(adjust_managed_page_count);
 

-- 
1.9.1

-- 
Michal Hocko
SUSE Labs

-- 
Michal Hocko
SUSE Labs