The quilt patch titled
Subject: mm/memcontrol: respect zswap.writeback setting from parent cg too
has been removed from the -mm tree. Its filename was
mm-memcontrol-respect-zswapwriteback-setting-from-parent-cg-too.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Mike Yuan <me(a)yhndnzj.com>
Subject: mm/memcontrol: respect zswap.writeback setting from parent cg too
Date: Fri, 23 Aug 2024 16:27:06 +0000
Currently, the behavior of zswap.writeback wrt. the cgroup hierarchy
seems a bit odd. Unlike zswap.max, it doesn't honor the value from parent
cgroups. This surfaced when people tried to globally disable zswap
writeback, i.e. reserve physical swap space only for hibernation [1] -
disabling zswap.writeback only for the root cgroup results in subcgroups
with zswap.writeback=1 still performing writeback.
The inconsistency became more noticeable after I introduced the
MemoryZSwapWriteback= systemd unit setting [2] for controlling the knob.
The patch assumed that the kernel would enforce the value of parent
cgroups. It could probably be workarounded from systemd's side, by going
up the slice unit tree and inheriting the value. Yet I think it's more
sensible to make it behave consistently with zswap.max and friends.
[1] https://wiki.archlinux.org/title/Power_management/Suspend_and_hibernate#Dis…
[2] https://github.com/systemd/systemd/pull/31734
Link: https://lkml.kernel.org/r/20240823162506.12117-1-me@yhndnzj.com
Fixes: 501a06fe8e4c ("zswap: memcontrol: implement zswap writeback disabling")
Signed-off-by: Mike Yuan <me(a)yhndnzj.com>
Reviewed-by: Nhat Pham <nphamcs(a)gmail.com>
Acked-by: Yosry Ahmed <yosryahmed(a)google.com>
Cc: Johannes Weiner <hannes(a)cmpxchg.org>
Cc: Michal Hocko <mhocko(a)kernel.org>
Cc: Michal Koutn�� <mkoutny(a)suse.com>
Cc: Muchun Song <muchun.song(a)linux.dev>
Cc: Roman Gushchin <roman.gushchin(a)linux.dev>
Cc: Shakeel Butt <shakeel.butt(a)linux.dev>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
Documentation/admin-guide/cgroup-v2.rst | 7 ++++---
mm/memcontrol.c | 12 +++++++++---
2 files changed, 13 insertions(+), 6 deletions(-)
--- a/Documentation/admin-guide/cgroup-v2.rst~mm-memcontrol-respect-zswapwriteback-setting-from-parent-cg-too
+++ a/Documentation/admin-guide/cgroup-v2.rst
@@ -1717,9 +1717,10 @@ The following nested keys are defined.
entries fault back in or are written out to disk.
memory.zswap.writeback
- A read-write single value file. The default value is "1". The
- initial value of the root cgroup is 1, and when a new cgroup is
- created, it inherits the current value of its parent.
+ A read-write single value file. The default value is "1".
+ Note that this setting is hierarchical, i.e. the writeback would be
+ implicitly disabled for child cgroups if the upper hierarchy
+ does so.
When this is set to 0, all swapping attempts to swapping devices
are disabled. This included both zswap writebacks, and swapping due
--- a/mm/memcontrol.c~mm-memcontrol-respect-zswapwriteback-setting-from-parent-cg-too
+++ a/mm/memcontrol.c
@@ -3613,8 +3613,7 @@ mem_cgroup_css_alloc(struct cgroup_subsy
memcg1_soft_limit_reset(memcg);
#ifdef CONFIG_ZSWAP
memcg->zswap_max = PAGE_COUNTER_MAX;
- WRITE_ONCE(memcg->zswap_writeback,
- !parent || READ_ONCE(parent->zswap_writeback));
+ WRITE_ONCE(memcg->zswap_writeback, true);
#endif
page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
if (parent) {
@@ -5320,7 +5319,14 @@ void obj_cgroup_uncharge_zswap(struct ob
bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
{
/* if zswap is disabled, do not block pages going to the swapping device */
- return !zswap_is_enabled() || !memcg || READ_ONCE(memcg->zswap_writeback);
+ if (!zswap_is_enabled())
+ return true;
+
+ for (; memcg; memcg = parent_mem_cgroup(memcg))
+ if (!READ_ONCE(memcg->zswap_writeback))
+ return false;
+
+ return true;
}
static u64 zswap_current_read(struct cgroup_subsys_state *css,
_
Patches currently in -mm which might be from me(a)yhndnzj.com are
documentation-cgroup-v2-clarify-that-zswapwriteback-is-ignored-if-zswap-is-disabled.patch
selftests-test_zswap-add-test-for-hierarchical-zswapwriteback.patch
Xen domU instances do not boot on x86 with ACPI enabled, so the entire
ACPI subsystem is ultimately disabled. This causes acpi_mps_check()
to trigger a warning that the ACPI MPS table is not present, which then
disables APIC support on domU, breaking the CPU topology detection for
all vCPUs other than the boot vCPU.
Fixes: 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management")
Signed-off-by: Ariadne Conill <ariadne(a)ariadne.space>
Cc: x86(a)kernel.org
Cc: Thomas Gleixner <tglx(a)linutronix.de>
Cc: linux-kernel(a)vger.kernel.org
Cc: stable(a)vger.kernel.org
---
arch/x86/kernel/cpu/topology.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index 621a151ccf7d..38fa5ed816d6 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -429,7 +429,7 @@ void __init topology_apply_cmdline_limits_early(void)
unsigned int possible = nr_cpu_ids;
/* 'maxcpus=0' 'nosmp' 'nolapic' 'disableapic' 'noapic' */
- if (!setup_max_cpus || ioapic_is_disabled || apic_is_disabled)
+ if (!setup_max_cpus || ioapic_is_disabled || (apic_is_disabled && !xen_pv_domain()))
possible = 1;
/* 'possible_cpus=N' */
--
2.39.2