/*
* 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.
*
* 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/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 *cg_to_vmpressure(struct cgroup *cg)
{
return css_to_vmpressure(cgroup_subsys_state(cg, mem_cgroup_subsys_id));
}
static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
{
struct cgroup *cg = vmpressure_to_css(vmpr)->cgroup;
struct mem_cgroup *memcg = mem_cgroup_from_cont(cg);
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,
};
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;
}
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);
}
struct vmpressure_event {
struct eventfd_ctx *efd;
enum vmpressure_levels level;
struct list_head node;
};
static bool vmpressure_event(struct vmpressure *vmpr,
unsigned long scanned, unsigned long reclaimed)
{
struct vmpressure_event *ev;
enum vmpressure_levels level;
bool signalled = false;
level = vmpressure_calc_level(scanned, reclaimed);
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;
}
static void vmpressure_work_fn(struct work_struct *work)
{
struct vmpressure *vmpr = work_to_vmpressure(work);
unsigned long scanned;
unsigned long reclaimed;
/*
* 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.
*/
if (!vmpr->scanned)
return;
mutex_lock(&vmpr->sr_lock);
scanned = vmpr->scanned;
reclaimed = vmpr->reclaimed;
vmpr->scanned = 0;
vmpr->reclaimed = 0;
mutex_unlock(&vmpr->sr_lock);
do {
if (vmpressure_event(vmpr, scanned, reclaimed))
break;
/*
* If not handled, propagate the event upward into the
* hierarchy.
*/
} while ((vmpr = vmpressure_parent(vmpr)));
}
/**
* vmpressure() - Account memory pressure through scanned/reclaimed ratio
* @gfp: reclaimer's gfp mask
* @memcg: cgroup memory controller handle
* @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.
*
* This function does not return any value.
*/
void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
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;
mutex_lock(&vmpr->sr_lock);
vmpr->scanned += scanned;
vmpr->reclaimed += reclaimed;
scanned = vmpr->scanned;
mutex_unlock(&vmpr->sr_lock);
if (scanned < vmpressure_win || work_pending(&vmpr->work))
return;
schedule_work(&vmpr->work);
}
/**
* 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, vmpressure_win, 0);
}
/**
* vmpressure_register_event() - Bind vmpressure notifications to an eventfd
* @cg: cgroup that is interested in vmpressure notifications
* @cft: cgroup control files handle
* @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").
*
* This function should not be used directly, just pass it to (struct
* cftype).register_event, and then cgroup core will handle everything by
* itself.
*/
int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
struct eventfd_ctx *eventfd, const char *args)
{
struct vmpressure *vmpr = cg_to_vmpressure(cg);
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;
}
/**
* vmpressure_unregister_event() - Unbind eventfd from vmpressure
* @cg: cgroup handle
* @cft: cgroup control files 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).
*
* This function should not be used directly, just pass it to (struct
* cftype).unregister_event, and then cgroup core will handle everything
* by itself.
*/
void vmpressure_unregister_event(struct cgroup *cg, struct cftype *cft,
struct eventfd_ctx *eventfd)
{
struct vmpressure *vmpr = cg_to_vmpressure(cg);
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)
{
mutex_init(&vmpr->sr_lock);
mutex_init(&vmpr->events_lock);
INIT_LIST_HEAD(&vmpr->events);
INIT_WORK(&vmpr->work, vmpressure_work_fn);
}
