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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Wed, 11 Jan 2023 09:49:08 -0800
Message-ID: <CAJuCfpHCRL5B7SxqTgNbpJqhFwzROX4HAOH5KArO1iXNs_3Kcg@mail.gmail.com>
Subject: Re: [PATCH 08/41] mm: introduce CONFIG_PER_VMA_LOCK
To:     Michal Hocko <mhocko@suse.com>
Cc:     David Laight <David.Laight@aculab.com>,
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On Wed, Jan 11, 2023 at 9:37 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Wed 11-01-23 09:04:41, Suren Baghdasaryan wrote:
> > On Wed, Jan 11, 2023 at 8:44 AM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Wed 11-01-23 08:28:49, Suren Baghdasaryan wrote:
> > > [...]
> > > > Anyhow. Sounds like the overhead of the current design is small enough
> > > > to remove CONFIG_PER_VMA_LOCK and let it depend only on architecture
> > > > support?
> > >
> > > Yes. Further optimizations can be done on top. Let's not over optimize
> > > at this stage.
> >
> > Sure, I won't optimize any further.
> > Just to expand on your question. Original design would be problematic
> > for embedded systems like Android. It notoriously has a high number of
> > VMAs due to anonymous VMAs being named, which prevents them from
> > merging.
>
> What is the usual number of VMAs in that environment?

I've seen some games which had over 4000 VMAs but that's on the upper
side. In my calculations I used 40000 VMAs as a ballpark number and
rough calculations before size optimization would increase memory
consumption by ~2M (depending on the lock placement in vm_area_struct
it would vary a bit). In Android, the performance team flags any
change that exceeds 500KB, so it would raise questions.

>
> --
> Michal Hocko
> SUSE Labs