cregit-Linux how code gets into the kernel

Release 4.8 mm/vmpressure.c

Directory: mm
 * Linux VM pressure
 * Copyright 2012 Linaro Ltd.
 *                Anton Vorontsov <>
 * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
 * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation.

#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); }


anton vorontsovanton vorontsov24100.00%1100.00%

static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr) { struct cgroup_subsys_state *css = vmpressure_to_css(vmpr); struct mem_cgroup *memcg = mem_cgroup_from_css(css); memcg = parent_mem_cgroup(memcg); if (!memcg) return NULL; return memcg_to_vmpressure(memcg); }


anton vorontsovanton vorontsov5092.59%150.00%
tejun heotejun heo47.41%150.00%

enum vmpressure_levels { VMPRESSURE_LOW = 0, VMPRESSURE_MEDIUM, VMPRESSURE_CRITICAL, VMPRESSURE_NUM_LEVELS, }; static const char * const vmpressure_str_levels[] = { [VMPRESSURE_LOW] = "low", [VMPRESSURE_MEDIUM] = "medium", [VMPRESSURE_CRITICAL] = "critical", };
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; }


anton vorontsovanton vorontsov33100.00%1100.00%

static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned, unsigned long reclaimed) { unsigned long scale = scanned + reclaimed; unsigned long pressure; /* * 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; pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure, scanned, reclaimed); return vmpressure_level(pressure); }


anton vorontsovanton vorontsov67100.00%1100.00%

struct vmpressure_event { struct eventfd_ctx *efd; enum vmpressure_levels level; struct list_head node; };
static bool vmpressure_event(struct vmpressure *vmpr, enum vmpressure_levels level) { struct vmpressure_event *ev; bool signalled = false; mutex_lock(&vmpr->events_lock); list_for_each_entry(ev, &vmpr->events, node) { if (level >= ev->level) { eventfd_signal(ev->efd, 1); signalled = true; } } mutex_unlock(&vmpr->events_lock); return signalled; }


anton vorontsovanton vorontsov7496.10%150.00%
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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; 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)) break; /* * If not handled, propagate the event upward into the * hierarchy. */ } while ((vmpr = vmpressure_parent(vmpr))); }


anton vorontsovanton vorontsov8870.40%125.00%
johannes weinerjohannes weiner1814.40%125.00%
andrew mortonandrew morton1713.60%125.00%
michal hockomichal hocko21.60%125.00%

/** * 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 = 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 || memcg == root_mem_cgroup) 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. */ memcg->socket_pressure = jiffies + HZ; } } }


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anton vorontsovanton vorontsov9644.86%120.00%
hugh dickinshugh dickins31.40%120.00%
vladimir davydovvladimir davydov20.93%120.00%
michal hockomichal hocko20.93%120.00%

/** * 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); }


anton vorontsovanton vorontsov3694.74%150.00%
johannes weinerjohannes weiner25.26%150.00%

/** * 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 (used to set up a pressure level threshold) * * This function associates eventfd context with the vmpressure * infrastructure, so that the notifications will be delivered to the * @eventfd. The @args parameter is a string that denotes pressure level * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or * "critical"). * * To be used as memcg event method. */
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; int level; for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) { if (!strcmp(vmpressure_str_levels[level], args)) break; } if (level >= VMPRESSURE_NUM_LEVELS) return -EINVAL; ev = kzalloc(sizeof(*ev), GFP_KERNEL); if (!ev) return -ENOMEM; ev->efd = eventfd; ev->level = level; mutex_lock(&vmpr->events_lock); list_add(&ev->node, &vmpr->events); mutex_unlock(&vmpr->events_lock); return 0; }


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/** * 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); }


anton vorontsovanton vorontsov7594.94%150.00%
tejun heotejun heo45.06%150.00%

/** * 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); }


anton vorontsovanton vorontsov4397.73%150.00%
michal hockomichal hocko12.27%150.00%

/** * 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); }


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Overall Contributors

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tejun heotejun heo171.61%330.00%
andrew mortonandrew morton171.61%110.00%
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Directory: mm
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