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 217d8b335eede58ef7fecb62d811a6bfda5b74c5
Author: Hugh Dickins <[email protected]>
Date: Wed Jul 5 14:39:48 2023 +0800
ms/mm/memcg: fix refcount error while moving and swapping
It was hard to keep a test running, moving tasks between memcgs with
move_charge_at_immigrate, while swapping: mem_cgroup_id_get_many()'s
refcount is discovered to be 0 (supposedly impossible), so it is then
forced to REFCOUNT_SATURATED, and after thousands of warnings in quick
succession, the test is at last put out of misery by being OOM killed.
This is because of the way moved_swap accounting was saved up until the
task move gets completed in __mem_cgroup_clear_mc(), deferred from when
mem_cgroup_move_swap_account() actually exchanged old and new ids.
Concurrent activity can free up swap quicker than the task is scanned,
bringing id refcount down 0 (which should only be possible when
offlining).
Just skip that optimization: do that part of the accounting immediately.
Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap
charge move")
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Alex Shi <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: <[email protected]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
https://jira.vzint.dev/browse/PSBM-147036
(cherry picked from commit 8d22a9351035ef2ff12ef163a1091b8b8cf1e49c)
Signed-off-by: Pavel Tikhomirov <[email protected]>
=================
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 | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f86c395fe8ee..0ff99bf5abdb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7462,7 +7462,6 @@ static void __mem_cgroup_clear_mc(void)
page_counter_uncharge(&mc.to->memory, mc.moved_swap);
}
- mem_cgroup_id_get_many(mc.to, mc.moved_swap);
mc.moved_swap = 0;
}
@@ -7622,7 +7621,8 @@ put: /* get_mctgt_type() gets the
page */
ent = target.ent;
if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to))
{
mc.precharge--;
- /* we fixup refcnts and charges later. */
+ mem_cgroup_id_get_many(mc.to, 1);
+ /* we fixup other refcnts and charges later. */
mc.moved_swap++;
}
break;
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