CC: linux-mm
On 09/15/2017 02:37 PM, Mike Kravetz wrote: > 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 <mike.krav...@oracle.com> > 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 <mike.krav...@oracle.com> > --- > 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), >
