// 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 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);
}
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 = 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;
}
}
}
/**
* 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.
*/
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 = -1;
char *spec, *spec_orig;
char *token;
int ret = 0;
spec_orig = spec = kstrndup(args, MAX_VMPRESSURE_ARGS_LEN, GFP_KERNEL);
if (!spec) {
ret = -ENOMEM;
goto out;
}
/* Find required level */
token = strsep(&spec, ",");
level = match_string(vmpressure_str_levels, VMPRESSURE_NUM_LEVELS, token);
if (level < 0) {
ret = level;
goto out;
}
/* Find optional mode */
token = strsep(&spec, ",");
if (token) {
mode = match_string(vmpressure_str_modes, VMPRESSURE_NUM_MODES, token);
if (mode < 0) {
ret = mode;
goto out;
}
}
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);
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);
}
