linux-kernel - Re: [PATCH v9 2/3] mm: add a field to store names for private anonymous memory

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Date:   Thu, 30 Sep 2021 16:25:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Peter Xu <peterx@...hat.com>, rppt@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jann Horn <jannh@...gle.com>, apopple@...dia.com,
        John Hubbard <jhubbard@...dia.com>,
        Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
        fenghua.yu@...el.com, thunder.leizhen@...wei.com,
        Hugh Dickins <hughd@...gle.com>, feng.tang@...el.com,
        Jason Gunthorpe <jgg@...pe.ca>, Roman Gushchin <guro@...com>,
        Thomas Gleixner <tglx@...utronix.de>, krisman@...labora.com,
        chris.hyser@...cle.com, Peter Collingbourne <pcc@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jens Axboe <axboe@...nel.dk>, legion@...nel.org,
        Rolf Eike Beer <eb@...ix.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Muchun Song <songmuchun@...edance.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Thomas Cedeno <thomascedeno@...gle.com>, sashal@...nel.org,
        cxfcosmos@...il.com, Rasmus Villemoes <linux@...musvillemoes.dk>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v9 2/3] mm: add a field to store names for private
 anonymous memory

On Thu, Sep 30, 2021 at 11:56:12AM -0700, Suren Baghdasaryan wrote:
> I thought more about these alternative suggestions for userspace to
> record allocations but that would introduce considerable complexity
> into userspace. Userspace would have to collect and consolidate this
> data by some daemon, all users would have to query it for the data
> (IPC or something similar), in case this daemon crashes the data would
> need to be somehow recovered. So, in short, it's possible but makes
> things much more complex compared to proposed in-kernel
> implementation.

Agreed: this is something for the kernel to manage.

> OTOH, the only downside of the current implementation is the
> additional memory required to store anon vma names. I checked the
> memory consumption on the latest Android with these patches and
> because we share vma names during fork, the actual memory required to
> store vma names is no more than 600kB. Even on older phones like Pixel
> 3 with 4GB RAM, this is less than 0.015% of total memory. IMHO, this
> is an acceptable price to pay.

I think that's entirely fine. We don't end up with any GUP games, and
everything is refcounted.

I think a v10 with the various nits fixed would be a good next step
here. What do you think Matthew?

-- 
Kees Cook