The patch titled
Subject: mm: memcontrol: simplify the logic of objcg pinning memcg
has been added to the -mm tree. Its filename is
mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg.patch
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------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: memcontrol: simplify the logic of objcg pinning memcg
The obj_cgroup_release() and memcg_reparent_objcgs() are serialized by the
css_set_lock. We do not need to care about objcg->memcg being released in
the process of obj_cgroup_release(). So there is no need to pin memcg
before releasing objcg. Remove those pinning logic to simplfy the code.
There are only two places that modifies the objcg->memcg. One is the
initialization to objcg->memcg in the memcg_online_kmem(), another is
objcgs reparenting in the memcg_reparent_objcgs(). It is also impossible
for the two to run in parallel. So xchg() is unnecessary and it is enough
to use WRITE_ONCE().
Link: https://lkml.kernel.org/r/20210417043538.9793-7-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 20 ++++++--------------
1 file changed, 6 insertions(+), 14 deletions(-)
--- a/mm/memcontrol.c~mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg
+++ a/mm/memcontrol.c
@@ -261,7 +261,6 @@ static void obj_cgroup_uncharge_pages(st
static void obj_cgroup_release(struct percpu_ref *ref)
{
struct obj_cgroup *objcg = container_of(ref, struct obj_cgroup, refcnt);
- struct mem_cgroup *memcg;
unsigned int nr_bytes;
unsigned int nr_pages;
unsigned long flags;
@@ -291,11 +290,9 @@ static void obj_cgroup_release(struct pe
nr_pages = nr_bytes >> PAGE_SHIFT;
spin_lock_irqsave(&css_set_lock, flags);
- memcg = obj_cgroup_memcg(objcg);
if (nr_pages)
obj_cgroup_uncharge_pages(objcg, nr_pages);
list_del(&objcg->list);
- mem_cgroup_put(memcg);
spin_unlock_irqrestore(&css_set_lock, flags);
percpu_ref_exit(ref);
@@ -330,17 +327,12 @@ static void memcg_reparent_objcgs(struct
spin_lock_irq(&css_set_lock);
- /* Move active objcg to the parent's list */
- xchg(&objcg->memcg, parent);
- css_get(&parent->css);
- list_add(&objcg->list, &parent->objcg_list);
-
- /* Move already reparented objcgs to the parent's list */
- list_for_each_entry(iter, &memcg->objcg_list, list) {
- css_get(&parent->css);
- xchg(&iter->memcg, parent);
- css_put(&memcg->css);
- }
+ /* 1) Ready to reparent active objcg. */
+ list_add(&objcg->list, &memcg->objcg_list);
+ /* 2) Reparent active objcg and already reparented objcgs to parent. */
+ list_for_each_entry(iter, &memcg->objcg_list, list)
+ WRITE_ONCE(iter->memcg, parent);
+ /* 3) Move already reparented objcgs to the parent's list */
list_splice(&memcg->objcg_list, &parent->objcg_list);
spin_unlock_irq(&css_set_lock);
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
mm-memcontrol-fix-root_mem_cgroup-charging.patch
mm-memcontrol-fix-page-charging-in-page-replacement.patch
mm-memcontrol-bail-out-early-when-mm-in-get_mem_cgroup_from_mm.patch
mm-memcontrol-remove-the-pgdata-parameter-of-mem_cgroup_page_lruvec.patch
mm-memcontrol-simplify-lruvec_holds_page_lru_lock.patch
mm-memcontrol-rename-lruvec_holds_page_lru_lock-to-page_matches_lruvec.patch
mm-memcontrol-simplify-the-logic-of-objcg-pinning-memcg.patch
mm-memcontrol-move-obj_cgroup_uncharge_pages-out-of-css_set_lock.patch
mm-vmscan-remove-noinline_for_stack.patch
mm-memory_hotplug-factor-out-bootmem-core-functions-to-bootmem_infoc.patch
mm-hugetlb-introduce-a-new-config-hugetlb_page_free_vmemmap.patch
mm-hugetlb-gather-discrete-indexes-of-tail-page.patch
mm-hugetlb-free-the-vmemmap-pages-associated-with-each-hugetlb-page.patch
mm-hugetlb-defer-freeing-of-hugetlb-pages.patch
mm-hugetlb-alloc-the-vmemmap-pages-associated-with-each-hugetlb-page.patch
mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap.patch
mm-memory_hotplug-disable-memmap_on_memory-when-hugetlb_free_vmemmap-enabled.patch
mm-hugetlb-introduce-nr_free_vmemmap_pages-in-the-struct-hstate.patch
