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

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Message-ID: <YV6rksRHr2iSWR3S@dhcp22.suse.cz>
Date:   Thu, 7 Oct 2021 10:10:58 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Pavel Machek <pavel@....cz>, 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>,
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        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Randy Dunlap <rdunlap@...radead.org>,
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Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

On Wed 06-10-21 11:18:31, Suren Baghdasaryan wrote:
> On Wed, Oct 6, 2021 at 10:58 AM Pavel Machek <pavel@....cz> wrote:
[...]
> > That "central facility" option can be as simple as "mkdir
> > /somewhere/sanitized_id", using inode numbers for example. You don't
> > really need IPC.
> 
> 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

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.
-- 
Michal Hocko
SUSE Labs