The commit is pushed to "branch-rh7-3.10.0-1160.90.1.vz7.200.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.90.1.vz7.200.4
------>
commit c090af3a18595ef850087d3428fea38a9346b4b3
Author: Vladimir Davydov <vdavy...@virtuozzo.com>
Date: Wed Jul 5 14:39:46 2023 +0800
ms/mm: memcontrol: fix swap counter leak on swapout from offline cgroup
An offline memory cgroup might have anonymous memory or shmem left
charged to it and no swap. Since only swap entries pin the id of an
offline cgroup, such a cgroup will have no id and so an attempt to
swapout its anon/shmem will not store memory cgroup info in the swap
cgroup map. As a result, memcg->swap or memcg->memsw will never get
uncharged from it and any of its ascendants.
Fix this by always charging swapout to the first ancestor cgroup that
hasn't released its id yet.
[han...@cmpxchg.org: add comment to mem_cgroup_swapout]
[vdavy...@virtuozzo.com: use WARN_ON_ONCE() in mem_cgroup_id_get_online()]
Link: http://lkml.kernel.org/r/20160803123445.GJ13263@esperanza
mFixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after
many small jobs")
Link:
http://lkml.kernel.org/r/5336daa5c9a32e776067773d9da655d2dc126491.1470219853.git.vdavy...@virtuozzo.com
Signed-off-by: Vladimir Davydov <vdavy...@virtuozzo.com>
Acked-by: Johannes Weiner <han...@cmpxchg.org>
Acked-by: Michal Hocko <mho...@suse.com>
Cc: <sta...@vger.kernel.org> [3.19+]
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
https://jira.vzint.dev/browse/PSBM-147036
(cherry picked from commit 1f47b61fb4077936465dcde872a4e5cc4fe708da)
Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
=================
Patchset description:
memcg: release id when offlinging cgroup
We see that container user can deplete memory cgroup ids on the system
(64k) and prevent further memory cgroup creation. In crash collected by
our customer in such a situation we see that mem_cgroup_idr is full of
cgroups from one container with same exact path (cgroup of docker
service), cgroups are not released because they have kmem charges, this
kmem charge is for a tmpfs dentry allocated from this cgroup. (And on
vz7 kernel it seems that such a dentry is only released after umounting
tmpfs or removing the corresponding file from tmpfs.)
So there is a valid way to hold kmem cgroup for a long time. Similar
thing was mentioned in mainstream with page cache holding kmem cgroup
for a long time. And they proposed a way to deal with it - just release
cgroup id early so that one can allocate new cgroups immediately.
Reproduce:
https://git.vzint.dev/users/ptikhomirov/repos/helpers/browse/memcg-related/test-mycg-tmpfs.sh
After this fix the number of memory cgroups in /proc/cgroups can now
show > 64k as we allow to leave memory cgroups hanging while releasing
their ids.
Note: Maybe it's a bad idea to allow container to eat kernel
memory with such a hanging cgroups, but yet I don't have better ideas.
https://jira.vzint.dev/browse/PSBM-147473
https://jira.vzint.dev/browse/PSBM-147036
---
mm/memcontrol.c | 39 ++++++++++++++++++++++++++++++++++-----
1 file changed, 34 insertions(+), 5 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 02dddc4c8cb8..d106e8f64997 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6676,6 +6676,24 @@ static void mem_cgroup_id_get(struct mem_cgroup *memcg)
atomic_inc(&memcg->id.ref);
}
+static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
+{
+ while (!atomic_inc_not_zero(&memcg->id.ref)) {
+ /*
+ * The root cgroup cannot be destroyed, so it's refcount must
+ * always be >= 1.
+ */
+ if (WARN_ON_ONCE(memcg == root_mem_cgroup)) {
+ VM_BUG_ON(1);
+ break;
+ }
+ memcg = parent_mem_cgroup(memcg);
+ if (!memcg)
+ memcg = root_mem_cgroup;
+ }
+ return memcg;
+}
+
static void mem_cgroup_id_put(struct mem_cgroup *memcg)
{
if (atomic_dec_and_test(&memcg->id.ref)) {
@@ -7756,7 +7774,7 @@ static void __init enable_swap_cgroup(void)
*/
void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
{
- struct mem_cgroup *memcg;
+ struct mem_cgroup *memcg, *swap_memcg;
struct page_cgroup *pc;
unsigned short oldid;
@@ -7775,17 +7793,28 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t
entry)
VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), page);
memcg = pc->mem_cgroup;
- mem_cgroup_id_get(memcg);
- oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
+ /*
+ * In case the memcg owning these pages has been offlined and doesn't
+ * have an ID allocated to it anymore, charge the closest online
+ * ancestor for the swap instead and transfer the memory+swap charge.
+ */
+ swap_memcg = mem_cgroup_id_get_online(memcg);
+ oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg));
VM_BUG_ON_PAGE(oldid, page);
- mem_cgroup_swap_statistics(memcg, true);
- this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PSWPOUT]);
+ mem_cgroup_swap_statistics(swap_memcg, true);
+ this_cpu_inc(swap_memcg->stat->events[MEM_CGROUP_EVENTS_PSWPOUT]);
pc->flags = 0;
if (!mem_cgroup_is_root(memcg))
page_counter_uncharge(&memcg->memory, 1);
+ if (memcg != swap_memcg) {
+ if (!mem_cgroup_is_root(swap_memcg))
+ page_counter_charge(&swap_memcg->memsw, 1);
+ page_counter_uncharge(&memcg->memsw, 1);
+ }
+
/* XXX: caller holds IRQ-safe mapping->tree_lock */
VM_BUG_ON(!irqs_disabled());
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