On Wed, Apr 5, 2023 at 6:23 PM Greg KH <gregkh@linuxfoundation.org> wrote:

> On Wed, Apr 05, 2023 at 06:01:07PM +0700, Shaun Tancheff wrote:
> > From: Shaun Tancheff <shaun.tancheff@hpe.com>
> >
> > For users that are unable to update to memcg-v2 this
> > provides a method where memcg-v1 can more effectively
> > apply enough memory pressure to effectively throttle
> > filesystem I/O or otherwise minimize being memcg oom
> > killed at the expense of reduced performance.
> >
> > This patch extends the memcg-v1 legacy sysfs entries
> > with:
> >     limit_in_bytes.min, limit_in_bytes.low and
> >     limit_in_bytes.high
> > Since old software will need to be updated to take
> > advantage of the new files a secondary method
> > of setting min, low and high based on a percentage
> > of the limit is also provided. The percentages
> > are determined by module parameters.
> >
> > The available module parameters can be set at
> > kernel boot time, for example:
> >    memcontrol.memcg_min=10
> >    memcontrol.memcg_low=30
> >    memcontrol.memcg_high=80
> >
> > Would set min to 10%, low to 30% and high to 80% of
> > the value written to:
> >   /sys/fs/cgroup/memory/<grp>/memory.limit_in_bytes
> >
> > Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
> > ---
> > v0: Initial hard coded limits by percent.
> > v1: Added sysfs access and module parameters for percent values to enable
> > v2: Fix 32-bit, remove need for missing __udivdi3
> >  mm/memcontrol.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 82 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 2eee092f8f11..3cf8386f4f45 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -73,6 +73,18 @@
> >
> >  #include <trace/events/vmscan.h>
> >
> > +static unsigned int memcg_v1_min_default_percent;
> > +module_param_named(memcg_min, memcg_v1_min_default_percent, uint, 0600);
> > +MODULE_PARM_DESC(memcg_min, "memcg v1 min default percent");
> > +
> > +static unsigned int memcg_v1_low_default_percent;
> > +module_param_named(memcg_low, memcg_v1_low_default_percent, uint, 0600);
> > +MODULE_PARM_DESC(memcg_low, "memcg v1 low default percent");
> > +
> > +static unsigned int memcg_v1_high_default_percent;
> > +module_param_named(memcg_high, memcg_v1_high_default_percent, uint,
> 0600);
> > +MODULE_PARM_DESC(memcg_high, "memcg v1 high default percent");
>
> This is not the 1990's, why are you using module parameters for this?
>
And this isn't a module, so why use module options, how are you supposed
> to set them?
>
Ah .. guess I'm a bit out of date.
The can be set either on the kernel command line or through sysfs,
nominally
  /sys/module/memcontrol/parameters/memcg_high
  /sys/module/memcontrol/parameters/memcg_low
  /sys/module/memcontrol/parameters/memcg_min

I will look at making these sysctl values instead.

And you didn't document them anywhere?
>
Next update will include documentation, as appropriate, Thanks!


> Also, why is this cc: stable?
>
Apologies, I understand this is not suitable for stable and will remove the
cc.

thanks,
>
> greg k-h
>