From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Kravetz Subject: [patch] mremap.2: Add description of old_size == 0 functionality Date: Fri, 15 Sep 2017 14:37:45 -0700 Message-ID: <20170915213745.6821-1-mike.kravetz@oracle.com> Return-path: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Cc: linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michal Hocko , Andrea Arcangeli , "Kirill A . Shutemov" , Vlastimil Babka , Anshuman Khandual , Mike Kravetz List-Id: linux-api@vger.kernel.org Since at least the 2.6 time frame, mremap would create a new mapping of the same pages if 'old_size == 0'. It would also leave the original mapping. This was used to create a 'duplicate mapping'. Document the behavior and return codes. But, also mention that the functionality is deprecated and discourage its use. A recent change was made to mremap so that an attempt to create a duplicate a private mapping will fail. commit dba58d3b8c5045ad89c1c95d33d01451e3964db7 Author: Mike Kravetz Date: Wed Sep 6 16:20:55 2017 -0700 mm/mremap: fail map duplication attempts for private mappings This return code is also documented here. Signed-off-by: Mike Kravetz --- man2/mremap.2 | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/man2/mremap.2 b/man2/mremap.2 index 98643c640..98df7d5fa 100644 --- a/man2/mremap.2 +++ b/man2/mremap.2 @@ -58,6 +58,21 @@ may be provided; see the description of .B MREMAP_FIXED below. .PP +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. +.PP In Linux the memory is divided into pages. A user process has (one or) several linear virtual memory segments. @@ -174,7 +189,12 @@ and or .B MREMAP_FIXED was specified without also specifying -.BR MREMAP_MAYMOVE . +.BR MREMAP_MAYMOVE ; +or \fIold_size\fP was zero and \fIold_address\fP does not refer to a +private anonymous mapping; +or \fIold_size\fP was zero and the +.BR MREMAP_MAYMOVE +flag was not specified. .TP .B ENOMEM The memory area cannot be expanded at the current virtual address, and the @@ -210,6 +230,7 @@ if the area cannot be populated. .BR brk (2), .BR getpagesize (2), .BR getrlimit (2), +.BR memfd_create(2), .BR mlock (2), .BR mmap (2), .BR sbrk (2), -- 2.13.5