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cgroup: add pids.peak interface for pids controller

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pids.peak tracks the high watermark of usage for number of pids. This
helps give a better baseline on which to set pids.max. Polling
pids.current isn't really feasible, since it would potentially miss
short-lived spikes.

This interface is analogous to memory.peak.

Signed-off-by: Josh Don <joshdon@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Josh Don 2022-08-31 15:49:03 -07:00 committed by Tejun Heo
parent dc79ec1b23
commit 5251c6c436
1 changed files with 35 additions and 2 deletions
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37
kernel/cgroup/pids.c
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@ -47,6 +47,7 @@ struct pids_cgroup {
*/
atomic64_t counter;
atomic64_t limit;
int64_t watermark;
/* Handle for "pids.events" */
struct cgroup_file events_file;
@ -85,6 +86,16 @@ static void pids_css_free(struct cgroup_subsys_state *css)
kfree(css_pids(css));
}
static void pids_update_watermark(struct pids_cgroup *p, int64_t nr_pids)
{
/*
* This is racy, but we don't need perfectly accurate tallying of
* the watermark, and this lets us avoid extra atomic overhead.
*/
if (nr_pids > READ_ONCE(p->watermark))
WRITE_ONCE(p->watermark, nr_pids);
}
/**
* pids_cancel - uncharge the local pid count
* @pids: the pid cgroup state
@ -128,8 +139,11 @@ static void pids_charge(struct pids_cgroup *pids, int num)
{
struct pids_cgroup *p;
for (p = pids; parent_pids(p); p = parent_pids(p))
atomic64_add(num, &p->counter);
for (p = pids; parent_pids(p); p = parent_pids(p)) {
int64_t new = atomic64_add_return(num, &p->counter);
pids_update_watermark(p, new);
}
}
/**
@ -156,6 +170,12 @@ static int pids_try_charge(struct pids_cgroup *pids, int num)
*/
if (new > limit)
goto revert;
/*
* Not technically accurate if we go over limit somewhere up
* the hierarchy, but that's tolerable for the watermark.
*/
pids_update_watermark(p, new);
}
return 0;
@ -311,6 +331,14 @@ static s64 pids_current_read(struct cgroup_subsys_state *css,
return atomic64_read(&pids->counter);
}
static s64 pids_peak_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
struct pids_cgroup *pids = css_pids(css);
return READ_ONCE(pids->watermark);
}
static int pids_events_show(struct seq_file *sf, void *v)
{
struct pids_cgroup *pids = css_pids(seq_css(sf));
@ -331,6 +359,11 @@ static struct cftype pids_files[] = {
.read_s64 = pids_current_read,
.flags = CFTYPE_NOT_ON_ROOT,
},
{
.name = "peak",
.flags = CFTYPE_NOT_ON_ROOT,
.read_s64 = pids_peak_read,
},
{
.name = "events",
.seq_show = pids_events_show,