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Diffstat (limited to 'mm/vmpressure.c')
| -rw-r--r-- | mm/vmpressure.c | 481 |
1 files changed, 481 insertions, 0 deletions
diff --git a/mm/vmpressure.c b/mm/vmpressure.c new file mode 100644 index 000000000..22c6689d9 --- /dev/null +++ b/mm/vmpressure.c @@ -0,0 +1,481 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Linux VM pressure + * + * Copyright 2012 Linaro Ltd. + * Anton Vorontsov <anton.vorontsov@linaro.org> + * + * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro, + * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg. + */ + +#include <linux/cgroup.h> +#include <linux/fs.h> +#include <linux/log2.h> +#include <linux/sched.h> +#include <linux/mm.h> +#include <linux/vmstat.h> +#include <linux/eventfd.h> +#include <linux/slab.h> +#include <linux/swap.h> +#include <linux/printk.h> +#include <linux/vmpressure.h> + +/* + * The window size (vmpressure_win) is the number of scanned pages before + * we try to analyze scanned/reclaimed ratio. So the window is used as a + * rate-limit tunable for the "low" level notification, and also for + * averaging the ratio for medium/critical levels. Using small window + * sizes can cause lot of false positives, but too big window size will + * delay the notifications. + * + * As the vmscan reclaimer logic works with chunks which are multiple of + * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well. + * + * TODO: Make the window size depend on machine size, as we do for vmstat + * thresholds. Currently we set it to 512 pages (2MB for 4KB pages). + */ +static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16; + +/* + * These thresholds are used when we account memory pressure through + * scanned/reclaimed ratio. The current values were chosen empirically. In + * essence, they are percents: the higher the value, the more number + * unsuccessful reclaims there were. + */ +static const unsigned int vmpressure_level_med = 60; +static const unsigned int vmpressure_level_critical = 95; + +/* + * When there are too little pages left to scan, vmpressure() may miss the + * critical pressure as number of pages will be less than "window size". + * However, in that case the vmscan priority will raise fast as the + * reclaimer will try to scan LRUs more deeply. + * + * The vmscan logic considers these special priorities: + * + * prio == DEF_PRIORITY (12): reclaimer starts with that value + * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed + * prio == 0 : close to OOM, kernel scans every page in an lru + * + * Any value in this range is acceptable for this tunable (i.e. from 12 to + * 0). Current value for the vmpressure_level_critical_prio is chosen + * empirically, but the number, in essence, means that we consider + * critical level when scanning depth is ~10% of the lru size (vmscan + * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one + * eights). + */ +static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10); + +static struct vmpressure *work_to_vmpressure(struct work_struct *work) +{ + return container_of(work, struct vmpressure, work); +} + +static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr) +{ + struct mem_cgroup *memcg = vmpressure_to_memcg(vmpr); + + memcg = parent_mem_cgroup(memcg); + if (!memcg) + return NULL; + return memcg_to_vmpressure(memcg); +} + +enum vmpressure_levels { + VMPRESSURE_LOW = 0, + VMPRESSURE_MEDIUM, + VMPRESSURE_CRITICAL, + VMPRESSURE_NUM_LEVELS, +}; + +enum vmpressure_modes { + VMPRESSURE_NO_PASSTHROUGH = 0, + VMPRESSURE_HIERARCHY, + VMPRESSURE_LOCAL, + VMPRESSURE_NUM_MODES, +}; + +static const char * const vmpressure_str_levels[] = { + [VMPRESSURE_LOW] = "low", + [VMPRESSURE_MEDIUM] = "medium", + [VMPRESSURE_CRITICAL] = "critical", +}; + +static const char * const vmpressure_str_modes[] = { + [VMPRESSURE_NO_PASSTHROUGH] = "default", + [VMPRESSURE_HIERARCHY] = "hierarchy", + [VMPRESSURE_LOCAL] = "local", +}; + +static enum vmpressure_levels vmpressure_level(unsigned long pressure) +{ + if (pressure >= vmpressure_level_critical) + return VMPRESSURE_CRITICAL; + else if (pressure >= vmpressure_level_med) + return VMPRESSURE_MEDIUM; + return VMPRESSURE_LOW; +} + +static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, + unsigned long reclaimed) +{ + unsigned long scale = scanned + reclaimed; + unsigned long pressure = 0; + + /* + * reclaimed can be greater than scanned for things such as reclaimed + * slab pages. shrink_node() just adds reclaimed pages without a + * related increment to scanned pages. + */ + if (reclaimed >= scanned) + goto out; + /* + * We calculate the ratio (in percents) of how many pages were + * scanned vs. reclaimed in a given time frame (window). Note that + * time is in VM reclaimer's "ticks", i.e. number of pages + * scanned. This makes it possible to set desired reaction time + * and serves as a ratelimit. + */ + pressure = scale - (reclaimed * scale / scanned); + pressure = pressure * 100 / scale; + +out: + pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure, + scanned, reclaimed); + + return vmpressure_level(pressure); +} + +struct vmpressure_event { + struct eventfd_ctx *efd; + enum vmpressure_levels level; + enum vmpressure_modes mode; + struct list_head node; +}; + +static bool vmpressure_event(struct vmpressure *vmpr, + const enum vmpressure_levels level, + bool ancestor, bool signalled) +{ + struct vmpressure_event *ev; + bool ret = false; + + mutex_lock(&vmpr->events_lock); + list_for_each_entry(ev, &vmpr->events, node) { + if (ancestor && ev->mode == VMPRESSURE_LOCAL) + continue; + if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH) + continue; + if (level < ev->level) + continue; + eventfd_signal(ev->efd, 1); + ret = true; + } + mutex_unlock(&vmpr->events_lock); + + return ret; +} + +static void vmpressure_work_fn(struct work_struct *work) +{ + struct vmpressure *vmpr = work_to_vmpressure(work); + unsigned long scanned; + unsigned long reclaimed; + enum vmpressure_levels level; + bool ancestor = false; + bool signalled = false; + + spin_lock(&vmpr->sr_lock); + /* + * Several contexts might be calling vmpressure(), so it is + * possible that the work was rescheduled again before the old + * work context cleared the counters. In that case we will run + * just after the old work returns, but then scanned might be zero + * here. No need for any locks here since we don't care if + * vmpr->reclaimed is in sync. + */ + scanned = vmpr->tree_scanned; + if (!scanned) { + spin_unlock(&vmpr->sr_lock); + return; + } + + reclaimed = vmpr->tree_reclaimed; + vmpr->tree_scanned = 0; + vmpr->tree_reclaimed = 0; + spin_unlock(&vmpr->sr_lock); + + level = vmpressure_calc_level(scanned, reclaimed); + + do { + if (vmpressure_event(vmpr, level, ancestor, signalled)) + signalled = true; + ancestor = true; + } while ((vmpr = vmpressure_parent(vmpr))); +} + +/** + * vmpressure() - Account memory pressure through scanned/reclaimed ratio + * @gfp: reclaimer's gfp mask + * @memcg: cgroup memory controller handle + * @tree: legacy subtree mode + * @scanned: number of pages scanned + * @reclaimed: number of pages reclaimed + * + * This function should be called from the vmscan reclaim path to account + * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw + * pressure index is then further refined and averaged over time. + * + * If @tree is set, vmpressure is in traditional userspace reporting + * mode: @memcg is considered the pressure root and userspace is + * notified of the entire subtree's reclaim efficiency. + * + * If @tree is not set, reclaim efficiency is recorded for @memcg, and + * only in-kernel users are notified. + * + * This function does not return any value. + */ +void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree, + unsigned long scanned, unsigned long reclaimed) +{ + struct vmpressure *vmpr; + + if (mem_cgroup_disabled()) + return; + + /* + * The in-kernel users only care about the reclaim efficiency + * for this @memcg rather than the whole subtree, and there + * isn't and won't be any in-kernel user in a legacy cgroup. + */ + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !tree) + return; + + vmpr = memcg_to_vmpressure(memcg); + + /* + * Here we only want to account pressure that userland is able to + * help us with. For example, suppose that DMA zone is under + * pressure; if we notify userland about that kind of pressure, + * then it will be mostly a waste as it will trigger unnecessary + * freeing of memory by userland (since userland is more likely to + * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That + * is why we include only movable, highmem and FS/IO pages. + * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so + * we account it too. + */ + if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS))) + return; + + /* + * If we got here with no pages scanned, then that is an indicator + * that reclaimer was unable to find any shrinkable LRUs at the + * current scanning depth. But it does not mean that we should + * report the critical pressure, yet. If the scanning priority + * (scanning depth) goes too high (deep), we will be notified + * through vmpressure_prio(). But so far, keep calm. + */ + if (!scanned) + return; + + if (tree) { + spin_lock(&vmpr->sr_lock); + scanned = vmpr->tree_scanned += scanned; + vmpr->tree_reclaimed += reclaimed; + spin_unlock(&vmpr->sr_lock); + + if (scanned < vmpressure_win) + return; + schedule_work(&vmpr->work); + } else { + enum vmpressure_levels level; + + /* For now, no users for root-level efficiency */ + if (!memcg || mem_cgroup_is_root(memcg)) + return; + + spin_lock(&vmpr->sr_lock); + scanned = vmpr->scanned += scanned; + reclaimed = vmpr->reclaimed += reclaimed; + if (scanned < vmpressure_win) { + spin_unlock(&vmpr->sr_lock); + return; + } + vmpr->scanned = vmpr->reclaimed = 0; + spin_unlock(&vmpr->sr_lock); + + level = vmpressure_calc_level(scanned, reclaimed); + + if (level > VMPRESSURE_LOW) { + /* + * Let the socket buffer allocator know that + * we are having trouble reclaiming LRU pages. + * + * For hysteresis keep the pressure state + * asserted for a second in which subsequent + * pressure events can occur. + */ + WRITE_ONCE(memcg->socket_pressure, jiffies + HZ); + } + } +} + +/** + * vmpressure_prio() - Account memory pressure through reclaimer priority level + * @gfp: reclaimer's gfp mask + * @memcg: cgroup memory controller handle + * @prio: reclaimer's priority + * + * This function should be called from the reclaim path every time when + * the vmscan's reclaiming priority (scanning depth) changes. + * + * This function does not return any value. + */ +void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio) +{ + /* + * We only use prio for accounting critical level. For more info + * see comment for vmpressure_level_critical_prio variable above. + */ + if (prio > vmpressure_level_critical_prio) + return; + + /* + * OK, the prio is below the threshold, updating vmpressure + * information before shrinker dives into long shrinking of long + * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0 + * to the vmpressure() basically means that we signal 'critical' + * level. + */ + vmpressure(gfp, memcg, true, vmpressure_win, 0); +} + +#define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2) + +/** + * vmpressure_register_event() - Bind vmpressure notifications to an eventfd + * @memcg: memcg that is interested in vmpressure notifications + * @eventfd: eventfd context to link notifications with + * @args: event arguments (pressure level threshold, optional mode) + * + * This function associates eventfd context with the vmpressure + * infrastructure, so that the notifications will be delivered to the + * @eventfd. The @args parameter is a comma-delimited string that denotes a + * pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium", + * or "critical") and an optional mode (one of vmpressure_str_modes, i.e. + * "hierarchy" or "local"). + * + * To be used as memcg event method. + * + * Return: 0 on success, -ENOMEM on memory failure or -EINVAL if @args could + * not be parsed. + */ +int vmpressure_register_event(struct mem_cgroup *memcg, + struct eventfd_ctx *eventfd, const char *args) +{ + struct vmpressure *vmpr = memcg_to_vmpressure(memcg); + struct vmpressure_event *ev; + enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH; + enum vmpressure_levels level; + char *spec, *spec_orig; + char *token; + int ret = 0; + + spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL); + if (!spec) + return -ENOMEM; + + /* Find required level */ + token = strsep(&spec, ","); + ret = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token); + if (ret < 0) + goto out; + level = ret; + + /* Find optional mode */ + token = strsep(&spec, ","); + if (token) { + ret = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token); + if (ret < 0) + goto out; + mode = ret; + } + + ev = kzalloc(sizeof(*ev), GFP_KERNEL); + if (!ev) { + ret = -ENOMEM; + goto out; + } + + ev->efd = eventfd; + ev->level = level; + ev->mode = mode; + + mutex_lock(&vmpr->events_lock); + list_add(&ev->node, &vmpr->events); + mutex_unlock(&vmpr->events_lock); + ret = 0; +out: + kfree(spec_orig); + return ret; +} + +/** + * vmpressure_unregister_event() - Unbind eventfd from vmpressure + * @memcg: memcg handle + * @eventfd: eventfd context that was used to link vmpressure with the @cg + * + * This function does internal manipulations to detach the @eventfd from + * the vmpressure notifications, and then frees internal resources + * associated with the @eventfd (but the @eventfd itself is not freed). + * + * To be used as memcg event method. + */ +void vmpressure_unregister_event(struct mem_cgroup *memcg, + struct eventfd_ctx *eventfd) +{ + struct vmpressure *vmpr = memcg_to_vmpressure(memcg); + struct vmpressure_event *ev; + + mutex_lock(&vmpr->events_lock); + list_for_each_entry(ev, &vmpr->events, node) { + if (ev->efd != eventfd) + continue; + list_del(&ev->node); + kfree(ev); + break; + } + mutex_unlock(&vmpr->events_lock); +} + +/** + * vmpressure_init() - Initialize vmpressure control structure + * @vmpr: Structure to be initialized + * + * This function should be called on every allocated vmpressure structure + * before any usage. + */ +void vmpressure_init(struct vmpressure *vmpr) +{ + spin_lock_init(&vmpr->sr_lock); + mutex_init(&vmpr->events_lock); + INIT_LIST_HEAD(&vmpr->events); + INIT_WORK(&vmpr->work, vmpressure_work_fn); +} + +/** + * vmpressure_cleanup() - shuts down vmpressure control structure + * @vmpr: Structure to be cleaned up + * + * This function should be called before the structure in which it is + * embedded is cleaned up. + */ +void vmpressure_cleanup(struct vmpressure *vmpr) +{ + /* + * Make sure there is no pending work before eventfd infrastructure + * goes away. + */ + flush_work(&vmpr->work); +} |