linux-kernel - Re: [PATCH v3 5/5] alloc_tag: config to store page allocation tag refs in page flags

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Message-ID: <CAJuCfpFk+1R8JQc+w6r6NUDsmjFnh9K1_42AvG+qTZq4vimwKg@mail.gmail.com>
Date: Mon, 21 Oct 2024 09:32:50 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Michal Hocko <mhocko@...e.com>
Cc: David Hildenbrand <david@...hat.com>, John Hubbard <jhubbard@...dia.com>, 
	Yosry Ahmed <yosryahmed@...gle.com>, akpm@...ux-foundation.org, 
	kent.overstreet@...ux.dev, corbet@....net, arnd@...db.de, mcgrof@...nel.org, 
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Subject: Re: [PATCH v3 5/5] alloc_tag: config to store page allocation tag
 refs in page flags

On Mon, Oct 21, 2024 at 9:23 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Mon 21-10-24 09:16:14, Suren Baghdasaryan wrote:
> > On Mon, Oct 21, 2024 at 8:57 AM Michal Hocko <mhocko@...e.com> wrote:
> > >
> > > On Mon 21-10-24 08:41:00, Suren Baghdasaryan wrote:
> > > > On Mon, Oct 21, 2024 at 8:34 AM Michal Hocko <mhocko@...e.com> wrote:
> > > > >
> > > > > On Mon 21-10-24 08:05:16, Suren Baghdasaryan wrote:
> > > > > [...]
> > > > > > Yeah, I thought about adding new values to "mem_profiling" but it's a
> > > > > > bit complicated. Today it's a tristate:
> > > > > >
> > > > > > mem_profiling=0|1|never
> > > > > >
> > > > > > 0/1 means we disable/enable memory profiling by default but the user
> > > > > > can enable it at runtime using a sysctl. This means that we enable
> > > > > > page_ext at boot even when it's set to 0.
> > > > > > "never" means we do not enable page_ext, memory profiling is disabled
> > > > > > and sysctl to enable it will not be exposed. Used when a distribution
> > > > > > has CONFIG_MEM_ALLOC_PROFILING=y but the user does not use it and does
> > > > > > not want to waste memory on enabling page_ext.
> > > > > >
> > > > > > I can add another option like "pgflags" but then it also needs to
> > > > > > specify whether we should enable or disable profiling by default
> > > > > > (similar to 0|1 for page_ext mode). IOW we will need to encode also
> > > > > > the default state we want. Something like this:
> > > > > >
> > > > > > mem_profiling=0|1|never|pgflags_on|pgflags_off
> > > > > >
> > > > > > Would this be acceptable?
> > > > >
> > > > > Isn't this overcomplicating it? Why cannot you simply go with
> > > > > mem_profiling={0|never|1}[,$YOUR_OPTIONS]
> > > > >
> > > > > While $YOUR_OPTIONS could be compress,fallback,ponies and it would apply
> > > > > or just be ignored if that is not applicable.
> > > >
> > > > Oh, you mean having 2 parts in the parameter with supported options being:
> > > >
> > > > mem_profiling=never
> > > > mem_profiling=0
> > > > mem_profiling=1
> > > > mem_profiling=0,pgflags
> > > > mem_profiling=1,pgflags
> > > >
> > > > Did I understand correctly? If so then yes, this should work.
> > >
> > > yes. I would just not call it pgflags because that just doesn't really
> > > tell what the option is to anybody but kernel developers. You could also
> > > have an option to override the default (disable profiling) failure strategy.
> >
> > Ok, how about "compressed" instead? Like this:
> >
> > mem_profiling=0,compressed
>
> Sounds good to me. And just to repeat, I do not really care about
> specific name but let's just stay away from something as specific as
> page flags because that is really not helping to understand the purpose
> but rather the underlying mechanism which is not telling much to most
> users outside of kernel developers.

Understood. Ok, I'll start changing my patchset to incorporate this
feedback and will post the new version this week.
Thanks for the input everyone!

>
> --
> Michal Hocko
> SUSE Labs