linux-kernel - Re: [PATCH v7 03/14] mm: Introduce memfile

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Message-ID: <00f1aa03-bc82-ffce-569b-e2d5c459992c@redhat.com>
Date:   Wed, 10 Aug 2022 12:05:42 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
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        Andrew Morton <akpm@...ux-foundation.org>,
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        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
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        ak@...ux.intel.com, aarcange@...hat.com, ddutile@...hat.com,
        dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 03/14] mm: Introduce memfile_notifier

On 10.08.22 11:22, Chao Peng wrote:
> On Fri, Aug 05, 2022 at 03:22:58PM +0200, David Hildenbrand wrote:
>> On 06.07.22 10:20, Chao Peng wrote:
>>> This patch introduces memfile_notifier facility so existing memory file
>>> subsystems (e.g. tmpfs/hugetlbfs) can provide memory pages to allow a
>>> third kernel component to make use of memory bookmarked in the memory
>>> file and gets notified when the pages in the memory file become
>>> invalidated.
>>
>> Stupid question, but why is this called "memfile_notifier" and not
>> "memfd_notifier". We're only dealing with memfd's after all ... which
>> are anonymous files essentially. Or what am I missing? Are there any
>> other plans for fs than plain memfd support that I am not aware of?
> 
> There were some discussions on this in v3.
>   https://lkml.org/lkml/2021/12/28/484
> Sean commented it's OK to abstract it from memfd but he also wants the
> kAPI (name) should not bind to memfd to make room for future non-memfd
> usages.

Sorry, but how is "memfile" any better? memfd abstracted to memfile?! :)

I understand Sean's suggestion about abstracting, but if the new name
makes it harder to grasp and there isn't really an alternative to memfd
in sight, I'm not so sure I enjoy the tried abstraction here.

Otherwise we'd have to get creative now and discuss something like
"file_population_notifer" or "mapping_population_notifer" and I am not
sure that our time is well spent doing so right now.

... as this is kernel-internal, we can always adjust the name as we
please later, once we *actually* now what the abstraction should be.
Until then I'd suggest to KIS and soft-glue this to memfd.

Or am I missing something important?

-- 
Thanks,

David / dhildenb