For reliable and timely aging on memcgs, one has to read the page age histograms on time. A kernel thread makes it easier by aging memcgs with valid refresh_interval when they can be refreshed, and also reduces the latency of any userspace consumers of the page age histogram.
The kerne aging thread is gated behind CONFIG_WORKINGSET_REPORT_AGING. Debugging stats may be added in the future for when aging cannot keep up with the configured refresh_interval.
Signed-off-by: Yuanchu Xie yuanchu@google.com --- include/linux/workingset_report.h | 11 ++- mm/Kconfig | 6 ++ mm/Makefile | 1 + mm/memcontrol.c | 8 +- mm/workingset_report.c | 15 +++- mm/workingset_report_aging.c | 127 ++++++++++++++++++++++++++++++ 6 files changed, 162 insertions(+), 6 deletions(-) create mode 100644 mm/workingset_report_aging.c
diff --git a/include/linux/workingset_report.h b/include/linux/workingset_report.h index ae412d408037..9294023db5a8 100644 --- a/include/linux/workingset_report.h +++ b/include/linux/workingset_report.h @@ -63,7 +63,16 @@ void wsr_remove_sysfs(struct node *node); * The next refresh time is stored in refresh_time. */ bool wsr_refresh_report(struct wsr_state *wsr, struct mem_cgroup *root, - struct pglist_data *pgdat); + struct pglist_data *pgdat, unsigned long *refresh_time); + +#ifdef CONFIG_WORKINGSET_REPORT_AGING +void wsr_wakeup_aging_thread(void); +#else /* CONFIG_WORKINGSET_REPORT_AGING */ +static inline void wsr_wakeup_aging_thread(void) +{ +} +#endif /* CONFIG_WORKINGSET_REPORT_AGING */ + #else static inline void wsr_init_lruvec(struct lruvec *lruvec) { diff --git a/mm/Kconfig b/mm/Kconfig index 03927ed2adbd..f8ff41408b9c 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1258,6 +1258,12 @@ config WORKINGSET_REPORT This option exports stats and events giving the user more insight into its memory working set.
+config WORKINGSET_REPORT_AGING + bool "Workingset report kernel aging thread" + depends on WORKINGSET_REPORT + help + Performs aging on memcgs with their configured refresh intervals. + source "mm/damon/Kconfig"
endmenu diff --git a/mm/Makefile b/mm/Makefile index ed05af2bb3e3..e9c9048e1e09 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -97,6 +97,7 @@ obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o obj-$(CONFIG_PAGE_COUNTER) += page_counter.o obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o obj-$(CONFIG_WORKINGSET_REPORT) += workingset_report.o +obj-$(CONFIG_WORKINGSET_REPORT_AGING) += workingset_report_aging.o ifdef CONFIG_SWAP obj-$(CONFIG_MEMCG) += swap_cgroup.o endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 48cdc9422794..547a2161b7e2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7281,12 +7281,12 @@ static ssize_t memory_ws_refresh_interval_write(struct kernfs_open_file *of, { unsigned int nid, msecs; struct wsr_state *wsr; + unsigned long old_interval; struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); ssize_t ret = memory_wsr_threshold_parse(buf, nbytes, &nid, &msecs);
if (ret < 0) return ret; - wsr = &mem_cgroup_lruvec(memcg, NODE_DATA(nid))->wsr;
mutex_lock(&wsr->page_age_lock); @@ -7305,9 +7305,13 @@ static ssize_t memory_ws_refresh_interval_write(struct kernfs_open_file *of, wsr->page_age = NULL; }
+ old_interval = READ_ONCE(wsr->refresh_interval); WRITE_ONCE(wsr->refresh_interval, msecs_to_jiffies(msecs)); unlock: mutex_unlock(&wsr->page_age_lock); + if (ret > 0 && msecs && + (!old_interval || jiffies_to_msecs(old_interval) > msecs)) + wsr_wakeup_aging_thread(); return ret; }
@@ -7358,7 +7362,7 @@ static int memory_ws_page_age_show(struct seq_file *m, void *v) if (!READ_ONCE(wsr->page_age)) continue;
- wsr_refresh_report(wsr, memcg, NODE_DATA(nid)); + wsr_refresh_report(wsr, memcg, NODE_DATA(nid), NULL); mutex_lock(&wsr->page_age_lock); if (!wsr->page_age) goto unlock; diff --git a/mm/workingset_report.c b/mm/workingset_report.c index 72f2cad85a0d..15118c4aecb1 100644 --- a/mm/workingset_report.c +++ b/mm/workingset_report.c @@ -274,7 +274,7 @@ static void copy_node_bins(struct pglist_data *pgdat, }
bool wsr_refresh_report(struct wsr_state *wsr, struct mem_cgroup *root, - struct pglist_data *pgdat) + struct pglist_data *pgdat, unsigned long *refresh_time) { struct wsr_page_age_histo *page_age; unsigned long refresh_interval = READ_ONCE(wsr->refresh_interval); @@ -291,10 +291,14 @@ bool wsr_refresh_report(struct wsr_state *wsr, struct mem_cgroup *root, goto unlock; if (page_age->timestamp && time_is_after_jiffies(page_age->timestamp + refresh_interval)) - goto unlock; + goto time; refresh_scan(wsr, root, pgdat, refresh_interval); copy_node_bins(pgdat, page_age); refresh_aggregate(page_age, root, pgdat); + +time: + if (refresh_time) + *refresh_time = page_age->timestamp + refresh_interval; unlock: mutex_unlock(&wsr->page_age_lock); return !!page_age; @@ -357,6 +361,7 @@ static ssize_t refresh_interval_store(struct kobject *kobj, unsigned int interval; int err; struct wsr_state *wsr = kobj_to_wsr(kobj); + unsigned long old_interval = 0;
err = kstrtouint(buf, 0, &interval); if (err) @@ -378,9 +383,13 @@ static ssize_t refresh_interval_store(struct kobject *kobj, wsr->page_age = NULL; }
+ old_interval = READ_ONCE(wsr->refresh_interval); WRITE_ONCE(wsr->refresh_interval, msecs_to_jiffies(interval)); unlock: mutex_unlock(&wsr->page_age_lock); + if (!err && interval && + (!old_interval || jiffies_to_msecs(old_interval) > interval)) + wsr_wakeup_aging_thread(); return err ?: len; }
@@ -470,7 +479,7 @@ static ssize_t page_age_show(struct kobject *kobj, struct kobj_attribute *attr, int ret = 0; struct wsr_state *wsr = kobj_to_wsr(kobj);
- wsr_refresh_report(wsr, NULL, kobj_to_pgdat(kobj)); + wsr_refresh_report(wsr, NULL, kobj_to_pgdat(kobj), NULL);
mutex_lock(&wsr->page_age_lock); if (!wsr->page_age) diff --git a/mm/workingset_report_aging.c b/mm/workingset_report_aging.c new file mode 100644 index 000000000000..91ad5020778a --- /dev/null +++ b/mm/workingset_report_aging.c @@ -0,0 +1,127 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Workingset report kernel aging thread + * + * Performs aging on behalf of memcgs with their configured refresh interval. + * While a userspace program can periodically read the page age breakdown + * per-memcg and trigger aging, the kernel performing aging is less overhead, + * more consistent, and more reliable for the use case where every memcg should + * be aged according to their refresh interval. + */ +#define pr_fmt(fmt) "workingset report aging: " fmt + +#include <linux/jiffies.h> +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/kthread.h> +#include <linux/memcontrol.h> +#include <linux/swap.h> +#include <linux/wait.h> +#include <linux/mmzone.h> +#include <linux/workingset_report.h> + +static DECLARE_WAIT_QUEUE_HEAD(aging_wait); +static bool refresh_pending; + +static bool do_aging_node(int nid, unsigned long *next_wake_time) +{ + struct mem_cgroup *memcg; + bool should_wait = true; + struct pglist_data *pgdat = NODE_DATA(nid); + + memcg = mem_cgroup_iter(NULL, NULL, NULL); + do { + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); + struct wsr_state *wsr = &lruvec->wsr; + unsigned long refresh_time; + + /* use returned time to decide when to wake up next */ + if (wsr_refresh_report(wsr, memcg, pgdat, &refresh_time)) { + if (should_wait) { + should_wait = false; + *next_wake_time = refresh_time; + } else if (time_before(refresh_time, *next_wake_time)) { + *next_wake_time = refresh_time; + } + } + + cond_resched(); + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); + + return should_wait; +} + +static int do_aging(void *unused) +{ + while (!kthread_should_stop()) { + int nid; + long timeout_ticks; + unsigned long next_wake_time; + bool should_wait = true; + + WRITE_ONCE(refresh_pending, false); + for_each_node_state(nid, N_MEMORY) { + unsigned long node_next_wake_time; + + if (do_aging_node(nid, &node_next_wake_time)) + continue; + if (should_wait) { + should_wait = false; + next_wake_time = node_next_wake_time; + } else if (time_before(node_next_wake_time, + next_wake_time)) { + next_wake_time = node_next_wake_time; + } + } + + if (should_wait) { + wait_event_interruptible(aging_wait, refresh_pending); + continue; + } + + /* sleep until next aging */ + timeout_ticks = next_wake_time - jiffies; + if (timeout_ticks > 0 && + timeout_ticks != MAX_SCHEDULE_TIMEOUT) { + schedule_timeout_idle(timeout_ticks); + continue; + } + } + return 0; +} + +/* Invoked when refresh_interval shortens or changes to a non-zero value. */ +void wsr_wakeup_aging_thread(void) +{ + WRITE_ONCE(refresh_pending, true); + wake_up_interruptible(&aging_wait); +} + +static struct task_struct *aging_thread; + +static int aging_init(void) +{ + struct task_struct *task; + + task = kthread_run(do_aging, NULL, "kagingd"); + + if (IS_ERR(task)) { + pr_err("Failed to create aging kthread\n"); + return PTR_ERR(task); + } + + aging_thread = task; + pr_info("module loaded\n"); + return 0; +} + +static void aging_exit(void) +{ + kthread_stop(aging_thread); + aging_thread = NULL; + pr_info("module unloaded\n"); +} + +module_init(aging_init); +module_exit(aging_exit);