mm, memcg: reclaim more aggressively before high allocator throttling
Patch series "mm, memcg: reclaim harder before high throttling", v2.
This patch (of 2):
In Facebook production, we've seen cases where cgroups have been put into
allocator throttling even when they appear to have a lot of slack file
caches which should be trivially reclaimable.
Looking more closely, the problem is that we only try a single cgroup
reclaim walk for each return to usermode before calculating whether or not
we should throttle. This single attempt doesn't produce enough pressure
to shrink for cgroups with a rapidly growing amount of file caches prior
to entering allocator throttling.
As an example, we see that threads in an affected cgroup are stuck in
allocator throttling:
# for i in $(cat cgroup.threads); do
> grep over_high "/proc/$i/stack"
> done
[<0>] mem_cgroup_handle_over_high+0x10b/0x150
[<0>] mem_cgroup_handle_over_high+0x10b/0x150
[<0>] mem_cgroup_handle_over_high+0x10b/0x150
...however, there is no I/O pressure reported by PSI, despite a lot of
slack file pages:
# cat memory.pressure
some avg10=78.50 avg60=84.99 avg300=84.53 total=5702440903
full avg10=78.50 avg60=84.99 avg300=84.53 total=5702116959
# cat io.pressure
some avg10=0.00 avg60=0.00 avg300=0.00 total=78051391
full avg10=0.00 avg60=0.00 avg300=0.00 total=78049640
# grep _file memory.stat
inactive_file 1370939392
active_file 661635072
This patch changes the behaviour to retry reclaim either until the current
task goes below the 10ms grace period, or we are making no reclaim
progress at all. In the latter case, we enter reclaim throttling as
before.
To a user, there's no intuitive reason for the reclaim behaviour to differ
from hitting memory.high as part of a new allocation, as opposed to
hitting memory.high because someone lowered its value. As such this also
brings an added benefit: it unifies the reclaim behaviour between the two.
There's precedent for this behaviour: we already do reclaim retries when
writing to memory.{high,max}, in max reclaim, and in the page allocator
itself.
Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Link: http://lkml.kernel.org/r/cover.1594640214.git.chris@chrisdown.name
Link: http://lkml.kernel.org/r/a4e23b59e9ef499b575ae73a8120ee089b7d3373.1594640214.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bb0d3ac..9b7a7d0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -73,6 +73,7 @@
struct mem_cgroup *root_mem_cgroup __read_mostly;
+/* The number of times we should retry reclaim failures before giving up. */
#define MEM_CGROUP_RECLAIM_RETRIES 5
/* Socket memory accounting disabled? */
@@ -2363,18 +2364,23 @@
return 0;
}
-static void reclaim_high(struct mem_cgroup *memcg,
- unsigned int nr_pages,
- gfp_t gfp_mask)
+static unsigned long reclaim_high(struct mem_cgroup *memcg,
+ unsigned int nr_pages,
+ gfp_t gfp_mask)
{
+ unsigned long nr_reclaimed = 0;
+
do {
if (page_counter_read(&memcg->memory) <=
READ_ONCE(memcg->memory.high))
continue;
memcg_memory_event(memcg, MEMCG_HIGH);
- try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
+ nr_reclaimed += try_to_free_mem_cgroup_pages(memcg, nr_pages,
+ gfp_mask, true);
} while ((memcg = parent_mem_cgroup(memcg)) &&
!mem_cgroup_is_root(memcg));
+
+ return nr_reclaimed;
}
static void high_work_func(struct work_struct *work)
@@ -2530,16 +2536,32 @@
{
unsigned long penalty_jiffies;
unsigned long pflags;
+ unsigned long nr_reclaimed;
unsigned int nr_pages = current->memcg_nr_pages_over_high;
+ int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
struct mem_cgroup *memcg;
+ bool in_retry = false;
if (likely(!nr_pages))
return;
memcg = get_mem_cgroup_from_mm(current->mm);
- reclaim_high(memcg, nr_pages, GFP_KERNEL);
current->memcg_nr_pages_over_high = 0;
+retry_reclaim:
+ /*
+ * The allocating task should reclaim at least the batch size, but for
+ * subsequent retries we only want to do what's necessary to prevent oom
+ * or breaching resource isolation.
+ *
+ * This is distinct from memory.max or page allocator behaviour because
+ * memory.high is currently batched, whereas memory.max and the page
+ * allocator run every time an allocation is made.
+ */
+ nr_reclaimed = reclaim_high(memcg,
+ in_retry ? SWAP_CLUSTER_MAX : nr_pages,
+ GFP_KERNEL);
+
/*
* memory.high is breached and reclaim is unable to keep up. Throttle
* allocators proactively to slow down excessive growth.
@@ -2567,6 +2589,16 @@
goto out;
/*
+ * If reclaim is making forward progress but we're still over
+ * memory.high, we want to encourage that rather than doing allocator
+ * throttling.
+ */
+ if (nr_reclaimed || nr_retries--) {
+ in_retry = true;
+ goto retry_reclaim;
+ }
+
+ /*
* If we exit early, we're guaranteed to die (since
* schedule_timeout_killable sets TASK_KILLABLE). This means we don't
* need to account for any ill-begotten jiffies to pay them off later.
