linux-kernel - Re: [PATCH v8 3/3] mm: add anonymous vma name refcounting

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJuCfpH+EsqTTok8sT1dXoO6_jz0UJa+PsCbX-_zUty6g-mPYQ@mail.gmail.com>
Date:   Mon, 30 Aug 2021 09:12:04 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Rolf Eike Beer <eb@...ix.com>
Cc:     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>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "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,
        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 v8 3/3] mm: add anonymous vma name refcounting

On Mon, Aug 30, 2021 at 12:03 AM Rolf Eike Beer <eb@...ix.com> wrote:
>
> Am Freitag, 27. August 2021, 21:18:58 CEST schrieb Suren Baghdasaryan:
> > While forking a process with high number (64K) of named anonymous vmas the
> > overhead caused by strdup() is noticeable. Experiments with ARM64 Android
> > device show up to 40% performance regression when forking a process with
> > 64k unpopulated anonymous vmas using the max name lengths vs the same
> > process with the same number of anonymous vmas having no name.
> > Introduce anon_vma_name refcounted structure to avoid the overhead of
> > copying vma names during fork() and when splitting named anonymous vmas.
> > When a vma is duplicated, instead of copying the name we increment the
> > refcount of this structure. Multiple vmas can point to the same
> > anon_vma_name as long as they increment the refcount. The name member of
> > anon_vma_name structure is assigned at structure allocation time and is
> > never changed. If vma name changes then the refcount of the original
> > structure is dropped, a new anon_vma_name structure is allocated
> > to hold the new name and the vma pointer is updated to point to the new
> > structure.
> > With this approach the fork() performance regressions is reduced 3-4x
> > times and with usecases using more reasonable number of VMAs (a few
> > thousand) the regressions is not measurable.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  include/linux/mm_types.h |  9 ++++++++-
> >  mm/madvise.c             | 42 +++++++++++++++++++++++++++++++++-------
> >  2 files changed, 43 insertions(+), 8 deletions(-)
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index bc029f3fca6a..32ac5dc5ebf3 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -63,6 +63,27 @@ static int madvise_need_mmap_write(int behavior)
> >       }
> >  }
> >
> > +static struct anon_vma_name *anon_vma_name_alloc(const char *name)
> > +{
> > +     struct anon_vma_name *anon_name;
> > +     size_t len = strlen(name);
> > +
> > +     /* Add 1 for NUL terminator at the end of the anon_name->name */
> > +     anon_name = kzalloc(sizeof(*anon_name) + len + 1,
> > +                         GFP_KERNEL);
> > +     kref_init(&anon_name->kref);
> > +     strcpy(anon_name->name, name);
> > +
> > +     return anon_name;
> > +}
>
> Given that you overwrite anything in that struct anyway this could be reduced
> to kmalloc(), no? And it definitely needs a NULL check.

Ack. I'll address both points in the next revision.
Thanks!
Suren.

>
> Eike
> --
> Rolf Eike Beer, emlix GmbH, http://www.emlix.com
> Fon +49 551 30664-0, Fax +49 551 30664-11
> Gothaer Platz 3, 37083 Göttingen, Germany
> Sitz der Gesellschaft: Göttingen, Amtsgericht Göttingen HR B 3160
> Geschäftsführung: Heike Jordan, Dr. Uwe Kracke – Ust-IdNr.: DE 205 198 055
>
> emlix - smart embedded open source