linux-kernel - Re: [patch] mremap.2: Add description of old

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Message-ID: <fb013ae6-6f47-248b-db8b-a0abae530377@redhat.com>
Date:   Mon, 18 Sep 2017 15:45:37 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, mtk.manpages@...il.com
Cc:     linux-man@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-mm@...ck.org
Subject: Re: [patch] mremap.2: Add description of old_size == 0 functionality

On 09/15/2017 11:53 PM, Mike Kravetz wrote:
> +If the value of \fIold_size\fP is zero, and \fIold_address\fP refers to
> +a private anonymous mapping, then
> +.BR mremap ()
> +will create a new mapping of the same pages. \fInew_size\fP
> +will be the size of the new mapping and the location of the new mapping
> +may be specified with \fInew_address\fP, see the description of
> +.B MREMAP_FIXED
> +below.  If a new mapping is requested via this method, then the
> +.B MREMAP_MAYMOVE
> +flag must also be specified.  This functionality is deprecated, and no
> +new code should be written to use this feature.  A better method of
> +obtaining multiple mappings of the same private anonymous memory is via the
> +.BR memfd_create()
> +system call.

Is there any particular reason to deprecate this?

In glibc, we cannot use memfd_create and keep the file descriptor around 
because the application can close descriptors beneath us.

(We might want to use alias mappings to avoid run-time code generation 
for PLT-less LD_AUDIT interceptors.)

Thanks,
Florian