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From:   David Hildenbrand <david@redhat.com>
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Subject: Re: [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas
Date:   Mon, 8 Feb 2021 22:38:03 +0100
Message-Id: <1F6A73CF-158A-4261-AA6C-1F5C77F4F326@redhat.com>
References: <20210208211326.GV242749@kernel.org>
Cc:     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>,
        Christopher Lameter <cl@linux.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>,
        Michal Hocko <mhocko@suse.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
        linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
        x86@kernel.org
In-Reply-To: <20210208211326.GV242749@kernel.org>
To:     Mike Rapoport <rppt@kernel.org>
Precedence: bulk


> Am 08.02.2021 um 22:13 schrieb Mike Rapoport <rppt@kernel.org>:
>=20
> =EF=BB=BFOn Mon, Feb 08, 2021 at 10:27:18AM +0100, David Hildenbrand wrote=
:
>> On 08.02.21 09:49, Mike Rapoport wrote:
>>=20
>> Some questions (and request to document the answers) as we now allow to h=
ave
>> unmovable allocations all over the place and I don't see a single comment=

>> regarding that in the cover letter:
>>=20
>> 1. How will the issue of plenty of unmovable allocations for user space b=
e
>> tackled in the future?
>>=20
>> 2. How has this issue been documented? E.g., interaction with ZONE_MOVABL=
E
>> and CMA, alloc_conig_range()/alloc_contig_pages?.
>=20
> Secretmem sets the mappings gfp mask to GFP_HIGHUSER, so it does not
> allocate movable pages at the first place.

That is not the point. Secretmem cannot go on CMA / ZONE_MOVABLE memory and b=
ehaves like long-term pinnings in that sense. This is a real issue when usin=
g a lot of sectremem.

Please have a look at what Pavel documents regarding long term pinnings and Z=
ONE_MOVABLE in his patches currently on the list.=