* Re: [PATCH] mm/mempolicy: failed to disable numa balancing
2022-12-02 19:59 ` Andrew Morton
@ 2022-12-03 3:44 ` Mina Almasry
2022-12-04 22:58 ` Yu Zhao
2022-12-16 10:46 ` Mel Gorman
2 siblings, 0 replies; 5+ messages in thread
From: Mina Almasry @ 2022-12-03 3:44 UTC (permalink / raw)
To: Andrew Morton; +Cc: tzm, linux-mm, linux-kernel, Mel Gorman
On Fri, Dec 2, 2022 at 12:00 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 2 Dec 2022 22:16:30 +0800 tzm <tcm1030@163.com> wrote:
>
> > It will be failed to disable numa balancing policy permanently by passing
> > <numa_balancing=disable> to boot cmdline parameters.
> > The numabalancing_override variable is int and 1 for enable -1 for disable.
> > So, !enumabalancing_override will always be true, which cause this bug.
>
> That's really old code!
>
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2865,7 +2865,7 @@ static void __init check_numabalancing_enable(void)
> > if (numabalancing_override)
> > set_numabalancing_state(numabalancing_override == 1);
> >
> > - if (num_online_nodes() > 1 && !numabalancing_override) {
> > + if (num_online_nodes() > 1 && (numabalancing_override == 1)) {
> > pr_info("%s automatic NUMA balancing. Configure with numa_balancing= or the kernel.numa_balancing sysctl\n",
> > numabalancing_default ? "Enabling" : "Disabling");
> > set_numabalancing_state(numabalancing_default);
>
> Looks right to me. Mel?
>
Maybe I'm missing something, but it looks wrong to me?
numabalancing_override is default initialized to 0, I think,
indicating that no override exists.
numabalancing_override == 1 indicates it has been overridden to true.
numabalancing_override == -1 indicates that it has been overridden to false.
The above code reads to me:
if (override_exists)
set_numabalancing_state(override_value)
if (num_online_nodes() > ! && !override_exists)
set_numabalancing_state(numabalancing_default)
A more clear fix for readability would be an early return between
these 2 if statements I think.
> After eight years, I wonder if we actually need this.
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm/mempolicy: failed to disable numa balancing
2022-12-02 19:59 ` Andrew Morton
2022-12-03 3:44 ` Mina Almasry
@ 2022-12-04 22:58 ` Yu Zhao
2022-12-16 10:46 ` Mel Gorman
2 siblings, 0 replies; 5+ messages in thread
From: Yu Zhao @ 2022-12-04 22:58 UTC (permalink / raw)
To: Andrew Morton; +Cc: tzm, linux-mm, linux-kernel, Mel Gorman
On Fri, Dec 2, 2022 at 1:00 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 2 Dec 2022 22:16:30 +0800 tzm <tcm1030@163.com> wrote:
>
> > It will be failed to disable numa balancing policy permanently by passing
> > <numa_balancing=disable> to boot cmdline parameters.
> > The numabalancing_override variable is int and 1 for enable -1 for disable.
> > So, !enumabalancing_override will always be true, which cause this bug.
!enumabalancing_override is false when enumabalancing_override = -1
(numa_balancing=disable).
> That's really old code!
>
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2865,7 +2865,7 @@ static void __init check_numabalancing_enable(void)
> > if (numabalancing_override)
> > set_numabalancing_state(numabalancing_override == 1);
> >
> > - if (num_online_nodes() > 1 && !numabalancing_override) {
> > + if (num_online_nodes() > 1 && (numabalancing_override == 1)) {
> > pr_info("%s automatic NUMA balancing. Configure with numa_balancing= or the kernel.numa_balancing sysctl\n",
> > numabalancing_default ? "Enabling" : "Disabling");
> > set_numabalancing_state(numabalancing_default);
>
> Looks right to me. Mel?
>
> After eight years, I wonder if we actually need this.
NAK.
The original code works as intended. This patch breaks my test with
CONFIG_NUMA_BALANCING_DEFAULT_ENABLED=n and numa_balancing=enable.
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm/mempolicy: failed to disable numa balancing
2022-12-02 19:59 ` Andrew Morton
2022-12-03 3:44 ` Mina Almasry
2022-12-04 22:58 ` Yu Zhao
@ 2022-12-16 10:46 ` Mel Gorman
2 siblings, 0 replies; 5+ messages in thread
From: Mel Gorman @ 2022-12-16 10:46 UTC (permalink / raw)
To: Andrew Morton; +Cc: tzm, linux-mm, linux-kernel
On Fri, Dec 02, 2022 at 11:59:54AM -0800, Andrew Morton wrote:
> On Fri, 2 Dec 2022 22:16:30 +0800 tzm <tcm1030@163.com> wrote:
>
> > It will be failed to disable numa balancing policy permanently by passing
> > <numa_balancing=disable> to boot cmdline parameters.
> > The numabalancing_override variable is int and 1 for enable -1 for disable.
> > So, !enumabalancing_override will always be true, which cause this bug.
>
> That's really old code!
>
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2865,7 +2865,7 @@ static void __init check_numabalancing_enable(void)
> > if (numabalancing_override)
> > set_numabalancing_state(numabalancing_override == 1);
> >
> > - if (num_online_nodes() > 1 && !numabalancing_override) {
> > + if (num_online_nodes() > 1 && (numabalancing_override == 1)) {
> > pr_info("%s automatic NUMA balancing. Configure with numa_balancing= or the kernel.numa_balancing sysctl\n",
> > numabalancing_default ? "Enabling" : "Disabling");
> > set_numabalancing_state(numabalancing_default);
>
> Looks right to me. Mel?
>
> After eight years, I wonder if we actually need this.
I don't think the patch is right aside from coding style issues such as
real names used in signed-off-by's.
The !numabalancing_override is checking "should the default be changed?",
itt's not checking if it should be enabled specifically. A better potential
fix would be something like this? (not actually tested)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 61aa9aedb728..fc649f8509f7 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2862,10 +2862,12 @@ static void __init check_numabalancing_enable(void)
numabalancing_default = true;
/* Parsed by setup_numabalancing. override == 1 enables, -1 disables */
- if (numabalancing_override)
+ if (numabalancing_override) {
set_numabalancing_state(numabalancing_override == 1);
+ return;
+ }
- if (num_online_nodes() > 1 && !numabalancing_override) {
+ if (num_online_nodes() > 1) {
pr_info("%s automatic NUMA balancing. Configure with numa_balancing= or the kernel.numa_balancing sysctl\n",
numabalancing_default ? "Enabling" : "Disabling");
set_numabalancing_state(numabalancing_default);
^ permalink raw reply [flat|nested] 5+ messages in thread