From: Kairui Song <kasong@tencent.com>

mem_cgroup_uncharge_swap() includes a mem_cgroup_disabled() check,
so the caller doesn't need to check that.

Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Chris Li <chrisl@kernel.org>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7b3503d12aaf..79900a486ed1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4609,7 +4609,7 @@ void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
 	 * correspond 1:1 to page and swap slot lifetimes: we charge the
 	 * page to memory here, and uncharge swap when the slot is freed.
 	 */
-	if (!mem_cgroup_disabled() && do_memsw_account()) {
+	if (do_memsw_account()) {
 		/*
 		 * The swap entry might not get freed for a long time,
 		 * let's not wait for it.  The page already received a
-- 
2.47.1

Hi, Kairui,

Sorry for jumping in so late.

Kairui Song <ryncsn@gmail.com> writes:

> From: Kairui Song <kasong@tencent.com>
>
> mem_cgroup_uncharge_swap() includes a mem_cgroup_disabled() check,
> so the caller doesn't need to check that.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>
> Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Acked-by: Chris Li <chrisl@kernel.org>
> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7b3503d12aaf..79900a486ed1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4609,7 +4609,7 @@ void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
>  	 * correspond 1:1 to page and swap slot lifetimes: we charge the
>  	 * page to memory here, and uncharge swap when the slot is freed.
>  	 */
> -	if (!mem_cgroup_disabled() && do_memsw_account()) {
> +	if (do_memsw_account()) {
>  		/*
>  		 * The swap entry might not get freed for a long time,
>  		 * let's not wait for it.  The page already received a

I take a look at memcontrol.c, it appears that almost all extern
functions check mem_cgroup_disabled() as the first step.  So I guess
that this is a convention of memcontrol.c?  And the benefit of the
change is minimal.  In contrast, if someone makes more changes to
mem_cgroup_swapin_uncharge_swap() in the future, he may forget to add
this back.  So, it may be unnecessary to make the change?

---
Best Regards,
Huang, Ying

On Sun, Dec 22, 2024 at 9:33 PM Huang, Ying
<ying.huang@linux.alibaba.com> wrote:
>
> Hi, Kairui,

Hi Ying,

>
> Sorry for jumping in so late.
>
> Kairui Song <ryncsn@gmail.com> writes:
>
> > From: Kairui Song <kasong@tencent.com>
> >
> > mem_cgroup_uncharge_swap() includes a mem_cgroup_disabled() check,
> > so the caller doesn't need to check that.
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
> > Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
> > Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> > Acked-by: Chris Li <chrisl@kernel.org>
> > ---
> >  mm/memcontrol.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 7b3503d12aaf..79900a486ed1 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -4609,7 +4609,7 @@ void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
> >        * correspond 1:1 to page and swap slot lifetimes: we charge the
> >        * page to memory here, and uncharge swap when the slot is freed.
> >        */
> > -     if (!mem_cgroup_disabled() && do_memsw_account()) {
> > +     if (do_memsw_account()) {
> >               /*
> >                * The swap entry might not get freed for a long time,
> >                * let's not wait for it.  The page already received a
>
> I take a look at memcontrol.c, it appears that almost all extern
> functions check mem_cgroup_disabled() as the first step.

Hmm, just checked memcontrol.c and I saw quite a few extern functions
not doing that, so I think that's not a convention.

> that this is a convention of memcontrol.c?  And the benefit of the
> change is minimal.  In contrast, if someone makes more changes to
> mem_cgroup_swapin_uncharge_swap() in the future, he may forget to add
> this back.  So, it may be unnecessary to make the change?

This change is minimal indeed, it only helps to remove a few unneeded
nop, still a gain though.

I think mem_cgroup_swapin_uncharge_swap should fade away in the future,
it's only for Cgroup V1, and it's a really simple function, just a
wrapper for mem_cgroup_uncharge_swap, so I think this is not a
problem?

If you are concerned about this, this patch can be dropped from this
series, rest of the patches still work the same.



>
> ---
> Best Regards,
> Huang, Ying

Kairui Song <ryncsn@gmail.com> writes:

> On Sun, Dec 22, 2024 at 9:33 PM Huang, Ying
> <ying.huang@linux.alibaba.com> wrote:
>>
>> Hi, Kairui,
>
> Hi Ying,
>
>>
>> Sorry for jumping in so late.
>>
>> Kairui Song <ryncsn@gmail.com> writes:
>>
>> > From: Kairui Song <kasong@tencent.com>
>> >
>> > mem_cgroup_uncharge_swap() includes a mem_cgroup_disabled() check,
>> > so the caller doesn't need to check that.
>> >
>> > Signed-off-by: Kairui Song <kasong@tencent.com>
>> > Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
>> > Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
>> > Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
>> > Acked-by: Chris Li <chrisl@kernel.org>
>> > ---
>> >  mm/memcontrol.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> > index 7b3503d12aaf..79900a486ed1 100644
>> > --- a/mm/memcontrol.c
>> > +++ b/mm/memcontrol.c
>> > @@ -4609,7 +4609,7 @@ void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
>> >        * correspond 1:1 to page and swap slot lifetimes: we charge the
>> >        * page to memory here, and uncharge swap when the slot is freed.
>> >        */
>> > -     if (!mem_cgroup_disabled() && do_memsw_account()) {
>> > +     if (do_memsw_account()) {
>> >               /*
>> >                * The swap entry might not get freed for a long time,
>> >                * let's not wait for it.  The page already received a
>>
>> I take a look at memcontrol.c, it appears that almost all extern
>> functions check mem_cgroup_disabled() as the first step.
>
> Hmm, just checked memcontrol.c and I saw quite a few extern functions
> not doing that, so I think that's not a convention.

I still think that it's a good idea to check whether memcg is disabled
in the outermost interfaces instead of being buried in some internal
functions.

>> that this is a convention of memcontrol.c?  And the benefit of the
>> change is minimal.  In contrast, if someone makes more changes to
>> mem_cgroup_swapin_uncharge_swap() in the future, he may forget to add
>> this back.  So, it may be unnecessary to make the change?
>
> This change is minimal indeed, it only helps to remove a few unneeded
> nop, still a gain though.

The benefit is minimal too.

> I think mem_cgroup_swapin_uncharge_swap should fade away in the future,

Good.  Then, we don't need to optimize it too.  Just let it fade away.

> it's only for Cgroup V1, and it's a really simple function, just a
> wrapper for mem_cgroup_uncharge_swap, so I think this is not a
> problem?
>
> If you are concerned about this, this patch can be dropped from this
> series, rest of the patches still work the same.

Just my 2 cents.

---
Best Regards,
Huang, Ying