Re: [PATCH v4 1/5] mm/memcg: Move mod_objcg_state() to memcontrol.c

From: Waiman Long
Date: Mon Apr 19 2021 - 13:26:38 EST

On 4/19/21 1:19 PM, Waiman Long wrote:
On 4/19/21 1:13 PM, Johannes Weiner wrote:
On Mon, Apr 19, 2021 at 12:18:29PM -0400, Waiman Long wrote:
On 4/19/21 11:21 AM, Waiman Long wrote:
On 4/19/21 11:14 AM, Johannes Weiner wrote:
On Sun, Apr 18, 2021 at 08:00:28PM -0400, Waiman Long wrote:
The mod_objcg_state() function is moved from mm/slab.h to
so that further optimization can be done to it in later patches without
exposing unnecessary details to other mm components.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
   mm/memcontrol.c | 13 +++++++++++++
   mm/slab.h       | 16 ++--------------
   2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e064ac0d850a..dc9032f28f2e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3150,6 +3150,19 @@ void __memcg_kmem_uncharge_page(struct
page *page, int order)
   +void mod_objcg_state(struct obj_cgroup *objcg, struct
pglist_data *pgdat,
+             enum node_stat_item idx, int nr)
+    struct mem_cgroup *memcg;
+    struct lruvec *lruvec = NULL;
+    rcu_read_lock();
+    memcg = obj_cgroup_memcg(objcg);
+    lruvec = mem_cgroup_lruvec(memcg, pgdat);
+    mod_memcg_lruvec_state(lruvec, idx, nr);
+    rcu_read_unlock();
It would be more naturally placed next to the others, e.g. below

But no deal breaker if there isn't another revision.

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Yes, there will be another revision by rebasing patch series on the
linux-next. I will move the function then.
OK, it turns out that mod_objcg_state() is only defined if
CONFIG_MEMCG_KMEM. That was why I put it in the CONFIG_MEMCG_KMEM block with
the other obj_stock functions. I think I will keep it there.
The CONFIG_MEMCG_KMEM has become sort of useless now. It used to be
configurable, but now it just means CONFIG_MEMCG && !CONFIG_SLOB. And
even that doesn't make sense because while slob doesn't support slab
object tracking, we can still do all the other stuff we do under
KMEM. I have a patch in the works to remove the symbol and ifdefs.

With that in mind, it's better to group the functions based on what
they do rather than based on CONFIG_MEMCG_KMEM. It's easier to just
remove another ifdef later than it is to reorder the functions.

OK, I will make the move then. Thanks for the explanation.

BTW, have you ever thought of moving the cgroup-v1 specific functions out into a separate memcontrol-v1.c file just like kernel/cgroup/cgroup-v1.c?

I thought of that before, but memcontrol.c is a frequently changed file and so a bit hard to do.