@@ -1299,6 +1299,13 @@ PAGE_SIZE multiple when read back.
monitors the limited cgroup to alleviate heavy reclaim
pressure.
+ If memory.high is opened with O_NONBLOCK then the synchronous
+ reclaim is bypassed. This is useful for admin processes that
+ need to dynamically adjust the job's memory limits without
+ expending their own CPU resources on memory reclamation. The
+ job will trigger the reclaim and/or get throttled on its
+ next charge request.
+
memory.max
A read-write single value file which exists on non-root
cgroups. The default is "max".
@@ -1316,6 +1323,13 @@ PAGE_SIZE multiple when read back.
Caller could retry them differently, return into userspace
as -ENOMEM or silently ignore in cases like disk readahead.
+ If memory.max is opened with O_NONBLOCK, then the synchronous
+ reclaim and oom-kill are bypassed. This is useful for admin
+ processes that need to dynamically adjust the job's memory limits
+ without expending their own CPU resources on memory reclamation.
+ The job will trigger the reclaim and/or oom-kill on its next
+ charge request.
+
memory.reclaim
A write-only nested-keyed file which exists for all cgroups.
@@ -4252,6 +4252,9 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
page_counter_set_high(&memcg->memory, high);
+ if (of->file->f_flags & O_NONBLOCK)
+ goto out;
+
for (;;) {
unsigned long nr_pages = page_counter_read(&memcg->memory);
unsigned long reclaimed;
@@ -4274,7 +4277,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
if (!reclaimed && !nr_retries--)
break;
}
-
+out:
memcg_wb_domain_size_changed(memcg);
return nbytes;
}
@@ -4301,6 +4304,9 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
xchg(&memcg->memory.max, max);
+ if (of->file->f_flags & O_NONBLOCK)
+ goto out;
+
for (;;) {
unsigned long nr_pages = page_counter_read(&memcg->memory);
@@ -4328,7 +4334,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
break;
cond_resched();
}
-
+out:
memcg_wb_domain_size_changed(memcg);
return nbytes;
}
Setting the max and high limits can trigger synchronous reclaim and/or oom-kill if the usage is higher than the given limit. This behavior is fine for newly created cgroups but it can cause issues for the node controller while setting limits for existing cgroups. In our production multi-tenant and overcommitted environment, we are seeing priority inversion when the node controller dynamically adjusts the limits of running jobs of different priorities. Based on the system situation, the node controller may reduce the limits of lower priority jobs and increase the limits of higher priority jobs. However we are seeing node controller getting stuck for long period of time while reclaiming from lower priority jobs while setting their limits and also spends a lot of its own CPU. One of the workaround we are trying is to fork a new process which sets the limit of the lower priority job along with setting an alarm to get itself killed if it get stuck in the reclaim for lower priority job. However we are finding it very unreliable and costly. Either we need a good enough time buffer for the alarm to be delivered after setting limit and potentialy spend a lot of CPU in the reclaim or be unreliable in setting the limit for much shorter but cheaper (less reclaim) alarms. Let's introduce new limit setting option which does not trigger reclaim and/or oom-kill and let the processes in the target cgroup to trigger reclaim and/or throttling and/or oom-kill in their next charge request. This will make the node controller on multi-tenant overcommitted environment much more reliable. Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> --- Changes since v1: - Instead of new interfaces use O_NONBLOCK flag (Greg, Roman & Tejun) Documentation/admin-guide/cgroup-v2.rst | 14 ++++++++++++++ mm/memcontrol.c | 10 ++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-)