linux-kernel - Re: [PATCH] memcg-v1: Enable setting memory min, low, high

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Message-ID: <2023040500-drinking-obvious-bd85@gregkh>
Date:   Wed, 5 Apr 2023 16:21:31 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Shaun Tancheff <shaun.tancheff@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Shaun Tancheff <shaun.tancheff@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg-v1: Enable setting memory min, low, high

On Wed, Apr 05, 2023 at 08:54:07PM +0700, Shaun Tancheff wrote:
> On Wed, Apr 5, 2023 at 6:23 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> > On Wed, Apr 05, 2023 at 06:01:07PM +0700, Shaun Tancheff wrote:
> > > From: Shaun Tancheff <shaun.tancheff@....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@....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

But again, memcontrol is not a module, right?

> I will look at making these sysctl values instead.

Yeah, just stick with that please.

thanks,

greg k-h