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Subject: Re: [patch] mremap.2: Add description of old_size == 0 functionality
To: Mike Kravetz <mike.kravetz@oracle.com>, mtk.manpages@gmail.com
Cc: linux-man@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Anshuman Khandual <khandual@linux.vnet.ibm.com>, linux-mm@kvack.org
References: <20170915213745.6821-1-mike.kravetz@oracle.com>
 <a6e59a7f-fd15-9e49-356e-ed439f17e9df@oracle.com>
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <fb013ae6-6f47-248b-db8b-a0abae530377@redhat.com>
Date: Mon, 18 Sep 2017 15:45:37 +0200
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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