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

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Date:   Thu, 4 Feb 2021 11:58:55 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     James Bottomley <jejb@...ux.ibm.com>,
        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>,
        Christopher Lameter <cl@...ux.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>,
        "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 Wed, Feb 03, 2021 at 10:12:22AM +0100, Michal Hocko wrote:
> On Tue 02-02-21 21:10:40, Mike Rapoport wrote:
> >   
> > Let me reiterate to make sure I don't misread your suggestion.
> > 
> > If we make secretmem an opt-in feature with, e.g. kernel parameter, the
> > pooling of large pages is unnecessary. In this case there is no limited
> > resource we need to protect because secretmem will allocate page by page.
> 
> Yes.
> 
> > Since there is no limited resource, we don't need special permissions
> > to access secretmem so we can move forward with a system call that creates
> > a mmapable file descriptor and save the hassle of a chardev.
> 
> Yes, I assume you implicitly assume mlock rlimit here.

Yes.

> Also memcg accounting should be in place. 

Right, without pools memcg accounting is no different from other
unevictable files.

> Wrt to the specific syscall, please document why existing interfaces are
> not a good fit as well. It would be also great to describe interaction
> with mlock itself (I assume the two to be incompatible - mlock will fail
> on and mlockall will ignore it).

The interaction with mlock() belongs more to the man page, but I don't mind
adding this to changelog as well.

-- 
Sincerely yours,
Mike.