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Date:   Thu, 28 Jan 2021 14:49:34 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Christoph Lameter <cl@linux.com>
Cc:     Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Bottomley <jejb@linux.ibm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
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        Shakeel Butt <shakeelb@google.com>,
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        Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize
 direct map fragmentation
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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