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![Andy Shevchenko](/assets/img/avatar_default.png)
The new helper returns index of the matching string in an array. We are going to use it here. Link: http://lkml.kernel.org/r/20180503203206.44046-1-andriy.shevchenko@linux.intel.com Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
472 lines
14 KiB
C
472 lines
14 KiB
C
/*
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* Linux VM pressure
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*
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* Copyright 2012 Linaro Ltd.
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* Anton Vorontsov <anton.vorontsov@linaro.org>
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*
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* Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
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* Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published
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* by the Free Software Foundation.
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*/
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#include <linux/cgroup.h>
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#include <linux/fs.h>
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#include <linux/log2.h>
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/vmstat.h>
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#include <linux/eventfd.h>
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#include <linux/slab.h>
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#include <linux/swap.h>
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#include <linux/printk.h>
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#include <linux/vmpressure.h>
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/*
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* The window size (vmpressure_win) is the number of scanned pages before
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* we try to analyze scanned/reclaimed ratio. So the window is used as a
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* rate-limit tunable for the "low" level notification, and also for
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* averaging the ratio for medium/critical levels. Using small window
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* sizes can cause lot of false positives, but too big window size will
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* delay the notifications.
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*
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* As the vmscan reclaimer logic works with chunks which are multiple of
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* SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
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*
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* TODO: Make the window size depend on machine size, as we do for vmstat
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* thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
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*/
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static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
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/*
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* These thresholds are used when we account memory pressure through
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* scanned/reclaimed ratio. The current values were chosen empirically. In
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* essence, they are percents: the higher the value, the more number
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* unsuccessful reclaims there were.
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*/
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static const unsigned int vmpressure_level_med = 60;
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static const unsigned int vmpressure_level_critical = 95;
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/*
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* When there are too little pages left to scan, vmpressure() may miss the
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* critical pressure as number of pages will be less than "window size".
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* However, in that case the vmscan priority will raise fast as the
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* reclaimer will try to scan LRUs more deeply.
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*
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* The vmscan logic considers these special priorities:
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*
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* prio == DEF_PRIORITY (12): reclaimer starts with that value
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* prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
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* prio == 0 : close to OOM, kernel scans every page in an lru
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*
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* Any value in this range is acceptable for this tunable (i.e. from 12 to
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* 0). Current value for the vmpressure_level_critical_prio is chosen
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* empirically, but the number, in essence, means that we consider
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* critical level when scanning depth is ~10% of the lru size (vmscan
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* scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
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* eights).
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*/
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static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);
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static struct vmpressure *work_to_vmpressure(struct work_struct *work)
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{
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return container_of(work, struct vmpressure, work);
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}
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static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
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{
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struct cgroup_subsys_state *css = vmpressure_to_css(vmpr);
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struct mem_cgroup *memcg = mem_cgroup_from_css(css);
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memcg = parent_mem_cgroup(memcg);
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if (!memcg)
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return NULL;
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return memcg_to_vmpressure(memcg);
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}
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enum vmpressure_levels {
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VMPRESSURE_LOW = 0,
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VMPRESSURE_MEDIUM,
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VMPRESSURE_CRITICAL,
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VMPRESSURE_NUM_LEVELS,
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};
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enum vmpressure_modes {
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VMPRESSURE_NO_PASSTHROUGH = 0,
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VMPRESSURE_HIERARCHY,
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VMPRESSURE_LOCAL,
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VMPRESSURE_NUM_MODES,
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};
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static const char * const vmpressure_str_levels[] = {
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[VMPRESSURE_LOW] = "low",
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[VMPRESSURE_MEDIUM] = "medium",
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[VMPRESSURE_CRITICAL] = "critical",
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};
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static const char * const vmpressure_str_modes[] = {
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[VMPRESSURE_NO_PASSTHROUGH] = "default",
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[VMPRESSURE_HIERARCHY] = "hierarchy",
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[VMPRESSURE_LOCAL] = "local",
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};
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static enum vmpressure_levels vmpressure_level(unsigned long pressure)
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{
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if (pressure >= vmpressure_level_critical)
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return VMPRESSURE_CRITICAL;
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else if (pressure >= vmpressure_level_med)
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return VMPRESSURE_MEDIUM;
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return VMPRESSURE_LOW;
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}
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static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
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unsigned long reclaimed)
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{
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unsigned long scale = scanned + reclaimed;
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unsigned long pressure = 0;
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/*
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* reclaimed can be greater than scanned for things such as reclaimed
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* slab pages. shrink_node() just adds reclaimed pages without a
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* related increment to scanned pages.
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*/
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if (reclaimed >= scanned)
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goto out;
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/*
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* We calculate the ratio (in percents) of how many pages were
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* scanned vs. reclaimed in a given time frame (window). Note that
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* time is in VM reclaimer's "ticks", i.e. number of pages
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* scanned. This makes it possible to set desired reaction time
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* and serves as a ratelimit.
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*/
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pressure = scale - (reclaimed * scale / scanned);
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pressure = pressure * 100 / scale;
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out:
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pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure,
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scanned, reclaimed);
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return vmpressure_level(pressure);
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}
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struct vmpressure_event {
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struct eventfd_ctx *efd;
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enum vmpressure_levels level;
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enum vmpressure_modes mode;
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struct list_head node;
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};
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static bool vmpressure_event(struct vmpressure *vmpr,
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const enum vmpressure_levels level,
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bool ancestor, bool signalled)
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{
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struct vmpressure_event *ev;
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bool ret = false;
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mutex_lock(&vmpr->events_lock);
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list_for_each_entry(ev, &vmpr->events, node) {
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if (ancestor && ev->mode == VMPRESSURE_LOCAL)
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continue;
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if (signalled && ev->mode == VMPRESSURE_NO_PASSTHROUGH)
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continue;
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if (level < ev->level)
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continue;
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eventfd_signal(ev->efd, 1);
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ret = true;
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}
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mutex_unlock(&vmpr->events_lock);
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return ret;
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}
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static void vmpressure_work_fn(struct work_struct *work)
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{
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struct vmpressure *vmpr = work_to_vmpressure(work);
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unsigned long scanned;
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unsigned long reclaimed;
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enum vmpressure_levels level;
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bool ancestor = false;
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bool signalled = false;
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spin_lock(&vmpr->sr_lock);
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/*
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* Several contexts might be calling vmpressure(), so it is
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* possible that the work was rescheduled again before the old
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* work context cleared the counters. In that case we will run
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* just after the old work returns, but then scanned might be zero
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* here. No need for any locks here since we don't care if
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* vmpr->reclaimed is in sync.
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*/
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scanned = vmpr->tree_scanned;
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if (!scanned) {
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spin_unlock(&vmpr->sr_lock);
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return;
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}
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reclaimed = vmpr->tree_reclaimed;
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vmpr->tree_scanned = 0;
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vmpr->tree_reclaimed = 0;
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spin_unlock(&vmpr->sr_lock);
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level = vmpressure_calc_level(scanned, reclaimed);
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do {
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if (vmpressure_event(vmpr, level, ancestor, signalled))
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signalled = true;
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ancestor = true;
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} while ((vmpr = vmpressure_parent(vmpr)));
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}
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/**
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* vmpressure() - Account memory pressure through scanned/reclaimed ratio
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* @gfp: reclaimer's gfp mask
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* @memcg: cgroup memory controller handle
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* @tree: legacy subtree mode
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* @scanned: number of pages scanned
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* @reclaimed: number of pages reclaimed
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*
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* This function should be called from the vmscan reclaim path to account
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* "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
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* pressure index is then further refined and averaged over time.
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*
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* If @tree is set, vmpressure is in traditional userspace reporting
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* mode: @memcg is considered the pressure root and userspace is
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* notified of the entire subtree's reclaim efficiency.
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*
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* If @tree is not set, reclaim efficiency is recorded for @memcg, and
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* only in-kernel users are notified.
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*
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* This function does not return any value.
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*/
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void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
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unsigned long scanned, unsigned long reclaimed)
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{
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
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/*
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* Here we only want to account pressure that userland is able to
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* help us with. For example, suppose that DMA zone is under
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* pressure; if we notify userland about that kind of pressure,
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* then it will be mostly a waste as it will trigger unnecessary
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* freeing of memory by userland (since userland is more likely to
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* have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
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* is why we include only movable, highmem and FS/IO pages.
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* Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
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* we account it too.
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*/
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if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
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return;
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/*
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* If we got here with no pages scanned, then that is an indicator
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* that reclaimer was unable to find any shrinkable LRUs at the
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* current scanning depth. But it does not mean that we should
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* report the critical pressure, yet. If the scanning priority
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* (scanning depth) goes too high (deep), we will be notified
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* through vmpressure_prio(). But so far, keep calm.
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*/
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if (!scanned)
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return;
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if (tree) {
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spin_lock(&vmpr->sr_lock);
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scanned = vmpr->tree_scanned += scanned;
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vmpr->tree_reclaimed += reclaimed;
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spin_unlock(&vmpr->sr_lock);
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if (scanned < vmpressure_win)
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return;
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schedule_work(&vmpr->work);
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} else {
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enum vmpressure_levels level;
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/* For now, no users for root-level efficiency */
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if (!memcg || memcg == root_mem_cgroup)
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return;
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spin_lock(&vmpr->sr_lock);
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scanned = vmpr->scanned += scanned;
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reclaimed = vmpr->reclaimed += reclaimed;
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if (scanned < vmpressure_win) {
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spin_unlock(&vmpr->sr_lock);
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return;
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}
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vmpr->scanned = vmpr->reclaimed = 0;
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spin_unlock(&vmpr->sr_lock);
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level = vmpressure_calc_level(scanned, reclaimed);
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if (level > VMPRESSURE_LOW) {
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/*
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* Let the socket buffer allocator know that
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* we are having trouble reclaiming LRU pages.
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*
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* For hysteresis keep the pressure state
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* asserted for a second in which subsequent
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* pressure events can occur.
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*/
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memcg->socket_pressure = jiffies + HZ;
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}
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}
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}
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/**
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* vmpressure_prio() - Account memory pressure through reclaimer priority level
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* @gfp: reclaimer's gfp mask
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* @memcg: cgroup memory controller handle
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* @prio: reclaimer's priority
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*
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* This function should be called from the reclaim path every time when
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* the vmscan's reclaiming priority (scanning depth) changes.
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*
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* This function does not return any value.
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*/
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void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
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{
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/*
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* We only use prio for accounting critical level. For more info
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* see comment for vmpressure_level_critical_prio variable above.
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*/
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if (prio > vmpressure_level_critical_prio)
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return;
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/*
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* OK, the prio is below the threshold, updating vmpressure
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* information before shrinker dives into long shrinking of long
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* range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
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* to the vmpressure() basically means that we signal 'critical'
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* level.
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*/
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vmpressure(gfp, memcg, true, vmpressure_win, 0);
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}
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#define MAX_VMPRESSURE_ARGS_LEN (strlen("critical") + strlen("hierarchy") + 2)
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/**
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* vmpressure_register_event() - Bind vmpressure notifications to an eventfd
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* @memcg: memcg that is interested in vmpressure notifications
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* @eventfd: eventfd context to link notifications with
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* @args: event arguments (pressure level threshold, optional mode)
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*
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* This function associates eventfd context with the vmpressure
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* infrastructure, so that the notifications will be delivered to the
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* @eventfd. The @args parameter is a comma-delimited string that denotes a
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* pressure level threshold (one of vmpressure_str_levels, i.e. "low", "medium",
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* or "critical") and an optional mode (one of vmpressure_str_modes, i.e.
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* "hierarchy" or "local").
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*
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* To be used as memcg event method.
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*/
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int vmpressure_register_event(struct mem_cgroup *memcg,
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struct eventfd_ctx *eventfd, const char *args)
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{
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
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struct vmpressure_event *ev;
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enum vmpressure_modes mode = VMPRESSURE_NO_PASSTHROUGH;
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enum vmpressure_levels level = -1;
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char *spec, *spec_orig;
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char *token;
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int ret = 0;
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spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
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if (!spec) {
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ret = -ENOMEM;
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goto out;
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}
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/* Find required level */
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token = strsep(&spec, ",");
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level = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
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if (level < 0) {
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ret = level;
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goto out;
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}
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/* Find optional mode */
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token = strsep(&spec, ",");
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if (token) {
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mode = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
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if (mode < 0) {
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ret = mode;
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goto out;
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}
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}
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ev = kzalloc(sizeof(*ev), GFP_KERNEL);
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if (!ev) {
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ret = -ENOMEM;
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goto out;
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}
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ev->efd = eventfd;
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ev->level = level;
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ev->mode = mode;
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mutex_lock(&vmpr->events_lock);
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list_add(&ev->node, &vmpr->events);
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mutex_unlock(&vmpr->events_lock);
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out:
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kfree(spec_orig);
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return ret;
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}
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/**
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* vmpressure_unregister_event() - Unbind eventfd from vmpressure
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* @memcg: memcg handle
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* @eventfd: eventfd context that was used to link vmpressure with the @cg
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*
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* This function does internal manipulations to detach the @eventfd from
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* the vmpressure notifications, and then frees internal resources
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* associated with the @eventfd (but the @eventfd itself is not freed).
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*
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* To be used as memcg event method.
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*/
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void vmpressure_unregister_event(struct mem_cgroup *memcg,
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struct eventfd_ctx *eventfd)
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{
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struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
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struct vmpressure_event *ev;
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mutex_lock(&vmpr->events_lock);
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list_for_each_entry(ev, &vmpr->events, node) {
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if (ev->efd != eventfd)
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continue;
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list_del(&ev->node);
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kfree(ev);
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break;
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}
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mutex_unlock(&vmpr->events_lock);
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}
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/**
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* vmpressure_init() - Initialize vmpressure control structure
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* @vmpr: Structure to be initialized
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*
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* This function should be called on every allocated vmpressure structure
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* before any usage.
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*/
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void vmpressure_init(struct vmpressure *vmpr)
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{
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spin_lock_init(&vmpr->sr_lock);
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mutex_init(&vmpr->events_lock);
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INIT_LIST_HEAD(&vmpr->events);
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INIT_WORK(&vmpr->work, vmpressure_work_fn);
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}
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/**
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* vmpressure_cleanup() - shuts down vmpressure control structure
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* @vmpr: Structure to be cleaned up
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*
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* This function should be called before the structure in which it is
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* embedded is cleaned up.
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*/
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void vmpressure_cleanup(struct vmpressure *vmpr)
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{
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/*
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* Make sure there is no pending work before eventfd infrastructure
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* goes away.
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*/
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flush_work(&vmpr->work);
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}
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