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systemd/SOURCES/1038-cgroup-drastically-simplify-caching-of-cgroups-membe.patch

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From 18d667eb7895b47dad3b4144b69e6e9e3afe4994 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 23 Nov 2018 01:07:34 +0100
Subject: [PATCH] cgroup: drastically simplify caching of cgroups members mask
Previously we tried to be smart: when a new unit appeared and it only
added controllers to the cgroup mask we'd update the cached members mask
in all parents by ORing in the controller flags in their cached values.
Unfortunately this was quite broken, as we missed some conditions when
this cache had to be reset (for example, when a unit got unloaded),
moreover the optimization doesn't work when a controller is removed
anyway (as in that case there's no other way for the parent to iterate
though all children if any other, remaining child unit still needs it).
Hence, let's simplify the logic substantially: instead of updating the
cache on the right events (which we didn't get right), let's simply
invalidate the cache, and generate it lazily when we encounter it later.
This should actually result in better behaviour as we don't have to
calculate the new members mask for a whole subtree whever we have the
suspicion something changed, but can delay it to the point where we
actually need the members mask.
This allows us to simplify things quite a bit, which is good, since
validating this cache for correctness is hard enough.
Fixes: #9512
(cherry picked from commit 5af8805872809e6de4cc4d9495cb1a904772ab4e)
Resolves: RHEL-9322
---
src/core/cgroup.c | 49 +++++------------------------------------
src/core/cgroup.h | 1 +
src/core/dbus-mount.c | 2 +-
src/core/dbus-scope.c | 2 +-
src/core/dbus-service.c | 2 +-
src/core/dbus-slice.c | 2 +-
src/core/dbus-socket.c | 2 +-
src/core/dbus-swap.c | 2 +-
src/core/unit.c | 3 ++-
src/core/unit.h | 2 --
10 files changed, 14 insertions(+), 53 deletions(-)
diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index bf829407b8..3276c876ec 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -1454,53 +1454,14 @@ bool unit_get_needs_bpf(Unit *u) {
return false;
}
-/* Recurse from a unit up through its containing slices, propagating
- * mask bits upward. A unit is also member of itself. */
-void unit_update_cgroup_members_masks(Unit *u) {
- CGroupMask m;
- bool more;
-
+void unit_invalidate_cgroup_members_masks(Unit *u) {
assert(u);
- /* Calculate subtree mask */
- m = unit_get_subtree_mask(u);
-
- /* See if anything changed from the previous invocation. If
- * not, we're done. */
- if (u->cgroup_subtree_mask_valid && m == u->cgroup_subtree_mask)
- return;
-
- more =
- u->cgroup_subtree_mask_valid &&
- ((m & ~u->cgroup_subtree_mask) != 0) &&
- ((~m & u->cgroup_subtree_mask) == 0);
-
- u->cgroup_subtree_mask = m;
- u->cgroup_subtree_mask_valid = true;
-
- if (UNIT_ISSET(u->slice)) {
- Unit *s = UNIT_DEREF(u->slice);
-
- if (more)
- /* There's more set now than before. We
- * propagate the new mask to the parent's mask
- * (not caring if it actually was valid or
- * not). */
-
- s->cgroup_members_mask |= m;
-
- else
- /* There's less set now than before (or we
- * don't know), we need to recalculate
- * everything, so let's invalidate the
- * parent's members mask */
+ /* Recurse invalidate the member masks cache all the way up the tree */
+ u->cgroup_members_mask_valid = false;
- s->cgroup_members_mask_valid = false;
-
- /* And now make sure that this change also hits our
- * grandparents */
- unit_update_cgroup_members_masks(s);
- }
+ if (UNIT_ISSET(u->slice))
+ unit_invalidate_cgroup_members_masks(UNIT_DEREF(u->slice));
}
const char *unit_get_realized_cgroup_path(Unit *u, CGroupMask mask) {
diff --git a/src/core/cgroup.h b/src/core/cgroup.h
index 535e328ab6..2ec8dd8fba 100644
--- a/src/core/cgroup.h
+++ b/src/core/cgroup.h
@@ -180,6 +180,7 @@ CGroupMask unit_get_enable_mask(Unit *u);
bool unit_get_needs_bpf(Unit *u);
+void unit_invalidate_cgroup_members_masks(Unit *u);
void unit_update_cgroup_members_masks(Unit *u);
void unit_add_to_cgroup_realize_queue(Unit *u);
diff --git a/src/core/dbus-mount.c b/src/core/dbus-mount.c
index a089b37e04..345494fd64 100644
--- a/src/core/dbus-mount.c
+++ b/src/core/dbus-mount.c
@@ -190,7 +190,7 @@ int bus_mount_set_property(
int bus_mount_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/dbus-scope.c b/src/core/dbus-scope.c
index 534302d188..8504352cbf 100644
--- a/src/core/dbus-scope.c
+++ b/src/core/dbus-scope.c
@@ -192,7 +192,7 @@ int bus_scope_set_property(
int bus_scope_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/dbus-service.c b/src/core/dbus-service.c
index 5f768a77c8..6db583492b 100644
--- a/src/core/dbus-service.c
+++ b/src/core/dbus-service.c
@@ -393,7 +393,7 @@ int bus_service_set_property(
int bus_service_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/dbus-slice.c b/src/core/dbus-slice.c
index 722a5688a5..effd5fa5d7 100644
--- a/src/core/dbus-slice.c
+++ b/src/core/dbus-slice.c
@@ -28,7 +28,7 @@ int bus_slice_set_property(
int bus_slice_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c
index 17494b80c8..dc74c82714 100644
--- a/src/core/dbus-socket.c
+++ b/src/core/dbus-socket.c
@@ -469,7 +469,7 @@ int bus_socket_set_property(
int bus_socket_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/dbus-swap.c b/src/core/dbus-swap.c
index b272d10113..353fa20132 100644
--- a/src/core/dbus-swap.c
+++ b/src/core/dbus-swap.c
@@ -63,7 +63,7 @@ int bus_swap_set_property(
int bus_swap_commit_properties(Unit *u) {
assert(u);
- unit_update_cgroup_members_masks(u);
+ unit_invalidate_cgroup_members_masks(u);
unit_realize_cgroup(u);
return 0;
diff --git a/src/core/unit.c b/src/core/unit.c
index 15c5bdf2a2..a7f610eca8 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -1583,7 +1583,8 @@ int unit_load(Unit *u) {
if (u->job_running_timeout != USEC_INFINITY && u->job_running_timeout > u->job_timeout)
log_unit_warning(u, "JobRunningTimeoutSec= is greater than JobTimeoutSec=, it has no effect.");
- unit_update_cgroup_members_masks(u);
+ /* We finished loading, let's ensure our parents recalculate the members mask */
+ unit_invalidate_cgroup_members_masks(u);
}
assert((u->load_state != UNIT_MERGED) == !u->merged_into);
diff --git a/src/core/unit.h b/src/core/unit.h
index b8b914711f..e2dd7949e5 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -265,7 +265,6 @@ typedef struct Unit {
char *cgroup_path;
CGroupMask cgroup_realized_mask;
CGroupMask cgroup_enabled_mask;
- CGroupMask cgroup_subtree_mask;
CGroupMask cgroup_members_mask;
int cgroup_inotify_wd;
@@ -341,7 +340,6 @@ typedef struct Unit {
bool cgroup_realized:1;
bool cgroup_members_mask_valid:1;
- bool cgroup_subtree_mask_valid:1;
UnitCGroupBPFState cgroup_bpf_state:2;
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