Hello Brian,
I see that MREMAP_DONTUNMAP has been merged. Thanks for the
patch below.
In addition to Vlastimil's comments, could you please take a look
at my comments below.
On 2/21/20 6:42 PM, Brian Geffon wrote:
> Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
> ---
> man2/mremap.2 | 30 +++++++++++++++++++++++++++++-
> 1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/man2/mremap.2 b/man2/mremap.2
> index d73fb64fa..54ec67b20 100644
> --- a/man2/mremap.2
> +++ b/man2/mremap.2
> @@ -26,7 +26,8 @@
> .\" 1996-04-12 Tom Bjorkholm <tomb@xxxxxxxxx>
> .\" Update for Linux 1.3.87 and later
> .\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
> -.\"
> +.\" 2020-02-05 Brian Geffon <bgeffon@xxxxxxxxxx>
> +.\" Update for MREMAP_DONTUNMAP.
No need to add this piece. This info is maintained
via the Git log these days.
> .TH MREMAP 2 2019-03-06 "Linux" "Linux Programmer's Manual"
> .SH NAME
> mremap \- remap a virtual memory address
> @@ -129,6 +130,13 @@ If
> is specified, then
> .B MREMAP_MAYMOVE
> must also be specified.
> +.TP
> +.BR MREMAP_DONTUNMAP " (since Linux 5.7)"
> +This flag which must be used in conjuction with
s/conjuction/conjunction/
> +.B MREMAP_MAYMOVE
> +remaps a mapping to a new address and it does not unmap the mapping at \fIold_address\fP. This flag can only be used with private anonymous mappings. Any access to the range specified at \fIold_address\fP after completion will result in a page fault. If a
Please wrap source lines to no more than about 75 columns.
Also, always start new sentences on new lines ("Semantic newlines").
As a general rule, I prefer formatting to be done like this:
.BR old_address .
rather than:
\fIold_address\fP.
(Yes, I know there's plenty of existing text that goes the other
way, but I try to avoid the \fX...\fP style for new text.
Re the "Any access to the range ... will result in a page fault", I think
it would be helpful to be more explicit. I presume that if we
access the range at old_address the mapping is repopulated with
zero-filled pages, right? It would be good to note that explicitly,
> +.BR userfaultfd (2)
> +was registered on the mapping specified by \fIold_address\fP it will continue to watch that mapping for faults.
(See comments above re wrapping and formatting.)
Perhaps it would be nice to have a short paragraph on use cases?
> .PP
> If the memory segment specified by
> .I old_address
> @@ -176,6 +184,8 @@ a value other than
> .B MREMAP_MAYMOVE
> or
> .B MREMAP_FIXED
> +or
> +.B MREMAP_DONTUNMAP
> was specified in
> .IR flags ;
> .IP *
> @@ -197,9 +207,17 @@ and
> .IR old_size ;
> .IP *
> .B MREMAP_FIXED
> +or
> +.B MREMAP_DONTUNMAP
> was specified without also specifying
> .BR MREMAP_MAYMOVE ;
> .IP *
> +.B MREMAP_DONTUNMAP
> +was specified with an \fIold_address\fP that was not private anonymous;
> +.IP *
> +.B MREMAP_DONTUNMAP
> +was specified and \fIold_size\fP was not equal to \fInew_size\fP;
> +.IP *
> \fIold_size\fP was zero and \fIold_address\fP does not refer to a
> shareable mapping (but see BUGS);
> .IP *
> @@ -209,10 +227,20 @@ flag was not specified.
> .RE
> .TP
> .B ENOMEM
> +Not enough memory was available to complete the operation.
> +Possible causes are:
> +.RS
> +.IP * 3
> The memory area cannot be expanded at the current virtual address, and the
> .B MREMAP_MAYMOVE
> flag is not set in \fIflags\fP.
> Or, there is not enough (virtual) memory available.
> +.IP *
> +.B MREMAP_DONTUNMAP
> +was used without
> +.B MREMAP_FIXED
> +causing a new mapping to be created that would exceed the virtual memory available or it would exceed the maximum number of allowed mappings.
(See comments above re wrapping.)
> +.RE
> .SH CONFORMING TO
> This call is Linux-specific, and should not be used in programs
> intended to be portable.
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
