From f1a7941243c102a44e8847e3b94ff4ff3ec56f25 Mon Sep 17 00:00:00 2001 From: Shakeel Butt Date: Mon, 24 Oct 2022 05:28:41 +0000 Subject: mm: convert mm's rss stats into percpu_counter Currently mm_struct maintains rss_stats which are updated on page fault and the unmapping codepaths. For page fault codepath the updates are cached per thread with the batch of TASK_RSS_EVENTS_THRESH which is 64. The reason for caching is performance for multithreaded applications otherwise the rss_stats updates may become hotspot for such applications. However this optimization comes with the cost of error margin in the rss stats. The rss_stats for applications with large number of threads can be very skewed. At worst the error margin is (nr_threads * 64) and we have a lot of applications with 100s of threads, so the error margin can be very high. Internally we had to reduce TASK_RSS_EVENTS_THRESH to 32. Recently we started seeing the unbounded errors for rss_stats for specific applications which use TCP rx0cp. It seems like vm_insert_pages() codepath does not sync rss_stats at all. This patch converts the rss_stats into percpu_counter to convert the error margin from (nr_threads * 64) to approximately (nr_cpus ^ 2). However this conversion enable us to get the accurate stats for situations where accuracy is more important than the cpu cost. This patch does not make such tradeoffs - we can just use percpu_counter_add_local() for the updates and percpu_counter_sum() (or percpu_counter_sync() + percpu_counter_read) for the readers. At the moment the readers are either procfs interface, oom_killer and memory reclaim which I think are not performance critical and should be ok with slow read. However I think we can make that change in a separate patch. Link: https://lkml.kernel.org/r/20221024052841.3291983-1-shakeelb@google.com Signed-off-by: Shakeel Butt Cc: Marek Szyprowski Signed-off-by: Andrew Morton --- include/linux/mm.h | 26 ++++++++------------------ include/linux/mm_types.h | 7 ++----- include/linux/mm_types_task.h | 13 ------------- include/linux/percpu_counter.h | 1 - include/linux/sched.h | 3 --- 5 files changed, 10 insertions(+), 40 deletions(-) (limited to 'include/linux') diff --git a/include/linux/mm.h b/include/linux/mm.h index f919befc8fac..0cb4e196d60b 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2052,40 +2052,30 @@ static inline bool get_user_page_fast_only(unsigned long addr, */ static inline unsigned long get_mm_counter(struct mm_struct *mm, int member) { - long val = atomic_long_read(&mm->rss_stat.count[member]); - -#ifdef SPLIT_RSS_COUNTING - /* - * counter is updated in asynchronous manner and may go to minus. - * But it's never be expected number for users. - */ - if (val < 0) - val = 0; -#endif - return (unsigned long)val; + return percpu_counter_read_positive(&mm->rss_stat[member]); } -void mm_trace_rss_stat(struct mm_struct *mm, int member, long count); +void mm_trace_rss_stat(struct mm_struct *mm, int member); static inline void add_mm_counter(struct mm_struct *mm, int member, long value) { - long count = atomic_long_add_return(value, &mm->rss_stat.count[member]); + percpu_counter_add(&mm->rss_stat[member], value); - mm_trace_rss_stat(mm, member, count); + mm_trace_rss_stat(mm, member); } static inline void inc_mm_counter(struct mm_struct *mm, int member) { - long count = atomic_long_inc_return(&mm->rss_stat.count[member]); + percpu_counter_inc(&mm->rss_stat[member]); - mm_trace_rss_stat(mm, member, count); + mm_trace_rss_stat(mm, member); } static inline void dec_mm_counter(struct mm_struct *mm, int member) { - long count = atomic_long_dec_return(&mm->rss_stat.count[member]); + percpu_counter_dec(&mm->rss_stat[member]); - mm_trace_rss_stat(mm, member, count); + mm_trace_rss_stat(mm, member); } /* Optimized variant when page is already known not to be PageAnon */ diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 2d5b1575ffe0..e86861ff5bbd 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -18,6 +18,7 @@ #include #include #include +#include #include @@ -626,11 +627,7 @@ struct mm_struct { unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */ - /* - * Special counters, in some configurations protected by the - * page_table_lock, in other configurations by being atomic. - */ - struct mm_rss_stat rss_stat; + struct percpu_counter rss_stat[NR_MM_COUNTERS]; struct linux_binfmt *binfmt; diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h index 0bb4b6da9993..5414b5c6a103 100644 --- a/include/linux/mm_types_task.h +++ b/include/linux/mm_types_task.h @@ -36,19 +36,6 @@ enum { NR_MM_COUNTERS }; -#if USE_SPLIT_PTE_PTLOCKS && defined(CONFIG_MMU) -#define SPLIT_RSS_COUNTING -/* per-thread cached information, */ -struct task_rss_stat { - int events; /* for synchronization threshold */ - int count[NR_MM_COUNTERS]; -}; -#endif /* USE_SPLIT_PTE_PTLOCKS */ - -struct mm_rss_stat { - atomic_long_t count[NR_MM_COUNTERS]; -}; - struct page_frag { struct page *page; #if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536) diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index 8ed5fba6d156..bde6c4c1f405 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -13,7 +13,6 @@ #include #include #include -#include /* percpu_counter batch for local add or sub */ #define PERCPU_COUNTER_LOCAL_BATCH INT_MAX diff --git a/include/linux/sched.h b/include/linux/sched.h index ffb6eb55cd13..079d299fa465 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -870,9 +870,6 @@ struct task_struct { struct mm_struct *mm; struct mm_struct *active_mm; -#ifdef SPLIT_RSS_COUNTING - struct task_rss_stat rss_stat; -#endif int exit_state; int exit_code; int exit_signal; -- cgit v1.2.3