From: Hongru Zhang On mobile devices, some user-space memory management components check memory pressure and fragmentation status periodically or via PSI, and take actions such as killing processes or performing memory compaction based on this information. Under high load scenarios, reading /proc/pagetypeinfo causes memory management components or memory allocation/free paths to be blocked for extended periods waiting for the zone lock, leading to the following issues: 1. Long interrupt-disabled spinlocks - occasionally exceeding 10ms on Qcom 8750 platforms, reducing system real-time performance 2. Memory management components being blocked for extended periods, preventing rapid acquisition of memory fragmentation information for critical memory management decisions and actions 3. Increased latency in memory allocation and free paths due to prolonged zone lock contention This patch adds per-migratetype counts to the buddy allocator in preparation for optimizing /proc/pagetypeinfo access. The optimized implementation: - Make per-migratetype count updates protected by zone lock on the write side while /proc/pagetypeinfo reads are lock-free, which reduces interrupt-disabled spinlock duration and improves system real-time performance (addressing issue #1) - Reduce blocking time for memory management components when reading /proc/pagetypeinfo, enabling more rapid acquisition of memory fragmentation information (addressing issue #2) - Minimize the critical section held during /proc/pagetypeinfo reads to reduce zone lock contention on memory allocation and free paths (addressing issue #3) The main overhead is a slight increase in latency on the memory allocation and free paths due to additional per-migratetype counting, with theoretically minimal impact on overall performance. Signed-off-by: Hongru Zhang --- include/linux/mmzone.h | 1 + mm/mm_init.c | 1 + mm/page_alloc.c | 7 ++++++- 3 files changed, 8 insertions(+), 1 deletion(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 7fb7331c5725..6eeefe6a3727 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -138,6 +138,7 @@ extern int page_group_by_mobility_disabled; struct free_area { struct list_head free_list[MIGRATE_TYPES]; unsigned long nr_free; + unsigned long mt_nr_free[MIGRATE_TYPES]; }; struct pglist_data; diff --git a/mm/mm_init.c b/mm/mm_init.c index 7712d887b696..dca2be8cc3b1 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1439,6 +1439,7 @@ static void __meminit zone_init_free_lists(struct zone *zone) for_each_migratetype_order(order, t) { INIT_LIST_HEAD(&zone->free_area[order].free_list[t]); zone->free_area[order].nr_free = 0; + zone->free_area[order].mt_nr_free[t] = 0; } #ifdef CONFIG_UNACCEPTED_MEMORY diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ed82ee55e66a..9431073e7255 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -818,6 +818,7 @@ static inline void __add_to_free_list(struct page *page, struct zone *zone, else list_add(&page->buddy_list, &area->free_list[migratetype]); area->nr_free++; + area->mt_nr_free[migratetype]++; if (order >= pageblock_order && !is_migrate_isolate(migratetype)) __mod_zone_page_state(zone, NR_FREE_PAGES_BLOCKS, nr_pages); @@ -840,6 +841,8 @@ static inline void move_to_free_list(struct page *page, struct zone *zone, get_pageblock_migratetype(page), old_mt, nr_pages); list_move_tail(&page->buddy_list, &area->free_list[new_mt]); + area->mt_nr_free[old_mt]--; + area->mt_nr_free[new_mt]++; account_freepages(zone, -nr_pages, old_mt); account_freepages(zone, nr_pages, new_mt); @@ -855,6 +858,7 @@ static inline void move_to_free_list(struct page *page, struct zone *zone, static inline void __del_page_from_free_list(struct page *page, struct zone *zone, unsigned int order, int migratetype) { + struct free_area *area = &zone->free_area[order]; int nr_pages = 1 << order; VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype, @@ -868,7 +872,8 @@ static inline void __del_page_from_free_list(struct page *page, struct zone *zon list_del(&page->buddy_list); __ClearPageBuddy(page); set_page_private(page, 0); - zone->free_area[order].nr_free--; + area->nr_free--; + area->mt_nr_free[migratetype]--; if (order >= pageblock_order && !is_migrate_isolate(migratetype)) __mod_zone_page_state(zone, NR_FREE_PAGES_BLOCKS, -nr_pages); -- 2.43.0