linux-kernel - Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation

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Message-ID: <YBLA7sEKn01HXd/U@dhcp22.suse.cz>
Date:   Thu, 28 Jan 2021 14:49:34 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, Hagen Paul Pfeifer <hagen@...u.net>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize
 direct map fragmentation

On Thu 28-01-21 13:28:10, Cristopher Lameter wrote:
> On Thu, 28 Jan 2021, Michal Hocko wrote:
> 
> > > So, if I understand your concerns correct this implementation has two
> > > issues:
> > > 1) allocation failure at page fault that causes unrecoverable OOM and
> > > 2) a possibility for an unprivileged user to deplete secretmem pool and
> > > cause (1) to others
> > >
> > > I'm not really familiar with OOM internals, but when I simulated an
> > > allocation failure in my testing only the allocating process and it's
> > > parent were OOM-killed and then the system continued normally.
> >
> > If you kill the allocating process then yes, it would work, but your
> > process might be the very last to be selected.
> 
> OOMs are different if you have a "constrained allocation". In that case it
> is the fault of the process who wanted memory with certain conditions.
> That memory is not available. General memory is available though. In that
> case the allocating process is killed.

I do not see this implementation would do anything like that. Neither
anything like that implemented in the oom killer. Constrained
allocations (cpusets/memcg/mempolicy) only do restrict their selection
to processes which belong to the same domain. So I am not really sure
what you are referring to. The is only a global knob to _always_ kill
the allocating process on OOM.

-- 
Michal Hocko
SUSE Labs