Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20211001205657.815551-1-surenb@google.com> <20211001205657.815551-3-surenb@google.com>
 <20211005184211.GA19804@duo.ucw.cz> <CAJuCfpE5JEThTMhwKPUREfSE1GYcTx4YSLoVhAH97fJH_qR0Zg@mail.gmail.com>
 <20211005200411.GB19804@duo.ucw.cz> <CAJuCfpFZkz2c0ZWeqzOAx8KFqk1ge3K-SiCMeu3dmi6B7bK-9w@mail.gmail.com>
 <efdffa68-d790-72e4-e6a3-80f2e194d811@nvidia.com> <YV1eCu0eZ+gQADNx@dhcp22.suse.cz>
 <6b15c682-72eb-724d-bc43-36ae6b79b91a@redhat.com>
In-Reply-To: <6b15c682-72eb-724d-bc43-36ae6b79b91a@redhat.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Wed, 6 Oct 2021 08:01:56 -0700
Message-ID: <CAJuCfpEPBM6ehQXgzp=g4SqtY6iaC8wuZ-CRE81oR1VOq7m4CA@mail.gmail.com>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
To:     David Hildenbrand <david@redhat.com>
Cc:     Michal Hocko <mhocko@suse.com>, John Hubbard <jhubbard@nvidia.com>,
        Pavel Machek <pavel@ucw.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Colin Cross <ccross@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Randy Dunlap <rdunlap@infradead.org>,
        Kalesh Singh <kaleshsingh@google.com>,
        Peter Xu <peterx@redhat.com>, rppt@kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        vincenzo.frascino@arm.com,
        =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= 
        <chinwen.chang@mediatek.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Jann Horn <jannh@google.com>, apopple@nvidia.com,
        Yu Zhao <yuzhao@google.com>, Will Deacon <will@kernel.org>,
        fenghua.yu@intel.com, thunder.leizhen@huawei.com,
        Hugh Dickins <hughd@google.com>, feng.tang@intel.com,
        Jason Gunthorpe <jgg@ziepe.ca>, Roman Gushchin <guro@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>, krisman@collabora.com,
        chris.hyser@oracle.com, Peter Collingbourne <pcc@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Jens Axboe <axboe@kernel.dk>, legion@kernel.org,
        Rolf Eike Beer <eb@emlix.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Thomas Cedeno <thomascedeno@google.com>, sashal@kernel.org,
        cxfcosmos@gmail.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm <linux-mm@kvack.org>,
        kernel-team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Oct 6, 2021 at 2:27 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 06.10.21 10:27, Michal Hocko wrote:
> > On Tue 05-10-21 23:57:36, John Hubbard wrote:
> > [...]
> >> 1) Yes, just leave the strings in the kernel, that's simple and
> >> it works, and the alternatives don't really help your case nearly
> >> enough.
> >
> > I do not have a strong opinion. Strings are easier to use but they
> > are more involved and the necessity of kref approach just underlines
> > that. There are going to be new allocations and that always can lead
> > to surprising side effects.  These are small (80B at maximum) so the
> > overall footpring shouldn't all that large by default but it can grow
> > quite large with a very high max_map_count. There are workloads which
> > really require the default to be set high (e.g. heavy mremap users). So
> > if anything all those should be __GFP_ACCOUNT and memcg accounted.
> >
> > I do agree that numbers are just much more simpler from accounting,
> > performance and implementation POV.
>
> +1
>
> I can understand that having a string can be quite beneficial e.g., when
> dumping mmaps. If only user space knows the id <-> string mapping, that
> can be quite tricky.
>
> However, I also do wonder if there would be a way to standardize/reserve
> ids, such that a given id always corresponds to a specific user. If we
> use an uint64_t for an id, there would be plenty room to reserve ids ...
>
> I'd really prefer if we can avoid using strings and instead using ids.

I wish it was that simple and for some names like [anon:.bss] or
[anon:dalvik-zygote space] reserving a unique id would work, however
some names like [anon:dalvik-/system/framework/boot-core-icu4j.art]
are generated dynamically at runtime and include package name.
Packages are constantly evolving, new ones are developed, names can
change, etc. So assigning a unique id for these names is not really
feasible.
That leaves us with the central facility option, which as I described
in my previous email would be prohibitive from performance POV (IPC
every time we have a new name or want to convert id to name).

I'm all for simplicity but the simple approach of using ids instead of
names unfortunately would not work for our usecases.

>
> --
> Thanks,
>
> David / dhildenb
>