linux-kernel - Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

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Message-ID: <20211007101527.GA26288@duo.ucw.cz>
Date:   Thu, 7 Oct 2021 12:15:27 +0200
From:   Pavel Machek <pavel@....cz>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Peter Xu <peterx@...hat.com>, rppt@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
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        Jann Horn <jannh@...gle.com>, apopple@...dia.com,
        Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
        fenghua.yu@...el.com, thunder.leizhen@...wei.com,
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        Peter Collingbourne <pcc@...gle.com>,
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        Jens Axboe <axboe@...nel.dk>, legion@...nel.org,
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        Cyrill Gorcunov <gorcunov@...il.com>,
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        cxfcosmos@...il.com, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

Hi!

> >> Hmm, so the suggestion is to have some directory which contains files
> >> representing IDs, each containing the string name of the associated
> >> vma? Then let's say we are creating a new VMA and want to name it. We
> >> would have to scan that directory, check all files and see if any of
> >> them contain the name we want to reuse the same ID.
> > 
> > I believe Pavel meant something as simple as
> > $ YOUR_FILE=$YOUR_IDS_DIR/my_string_name
> > $ touch $YOUR_FILE
> > $ stat -c %i $YOUR_FILE
> 
> So in terms of syscall overhead, that would be open(..., O_CREAT |
> O_CLOEXEC), fstat(), close() - or one could optimistically start by

You could get to two if you used mkdir instead of open.

> > YOUR_IDS_DIR can live on a tmpfs and you can even implement a policy on
> > top of that (who can generate new ids, gurantee uniqness etc...).
> > 
> > The above is certainly not for free of course but if you really need a
> > system wide consistency when using names then you need some sort of
> > central authority. How you implement that is not all that important
> > but I do not think we want to handle that in the kernel.
> 
> IDK. If the whole thing could be put behind a CONFIG_ knob, with _zero_
> overhead when not enabled (and I'm a bit worried about all the functions
> that grow an extra argument that gets passed around), I don't mind the
> string interface. But I don't really have a say either way.

If this is ever useful outside of Android, eventually distros will
have it enabled.

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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