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Date:   Tue, 5 Oct 2021 22:04:11 +0200
From:   Pavel Machek <>
To:     Suren Baghdasaryan <>
Cc:     Andrew Morton <>,
        Colin Cross <>,
        Sumit Semwal <>,
        Michal Hocko <>,
        Dave Hansen <>,
        Kees Cook <>,
        Matthew Wilcox <>,
        "Kirill A . Shutemov" <>,
        Vlastimil Babka <>,
        Johannes Weiner <>,
        Jonathan Corbet <>,
        Al Viro <>,
        Randy Dunlap <>,
        Kalesh Singh <>,
        Peter Xu <>,,
        Peter Zijlstra <>,
        Catalin Marinas <>,,
        Chinwen Chang (張錦文) 
        Axel Rasmussen <>,
        Andrea Arcangeli <>,
        Jann Horn <>,,
        John Hubbard <>,
        Yu Zhao <>, Will Deacon <>,,,
        Hugh Dickins <>,,
        Jason Gunthorpe <>, Roman Gushchin <>,
        Thomas Gleixner <>,,, Peter Collingbourne <>,
        "Eric W. Biederman" <>,
        Jens Axboe <>,,
        Rolf Eike Beer <>,
        Cyrill Gorcunov <>,
        Muchun Song <>,
        Viresh Kumar <>,
        Thomas Cedeno <>,,, Rasmus Villemoes <>,
        LKML <>,,,
        linux-mm <>,
        kernel-team <>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting


> > On Fri 2021-10-01 13:56:57, Suren Baghdasaryan wrote:
> > > While forking a process with high number (64K) of named anonymous vmas the
> > > overhead caused by strdup() is noticeable. Experiments with ARM64
> > Android
> >
> > I still believe you should simply use numbers and do the
> > numbers->strings mapping in userspace. We should not need to optimize
> > strdups in kernel...
> Here are complications with mapping numbers to strings in the userspace:
> Approach 1: hardcode number->string in some header file and let all
> tools use that mapping. The issue is that whenever that mapping
> changes all the tools that are using it (including 3rd party ones)
> have to be rebuilt. This is not really maintainable since we don't
> control 3rd party tools and even for the ones we control, it will be a
> maintenance issue figuring out which version of the tool used which
> header file.

1a) Just put it into a file in /etc... Similar to header file but

> Approach 2: have a centralized facility (a process or a DB)
> maintaining number->string mapping. This would require an additional
> request to this facility whenever we want to make a number->string
> conversion. Moreover, when we want to name a VMA, we would have to

I see it complicates userspace. But that's better than complicating
kernel, and I don't know what limits on strings you plan, but
considering you'll be outputing the strings in /proc... someone is
going to get confused with parsing.


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