Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx> --- man2/mremap.2 | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/man2/mremap.2 b/man2/mremap.2 index d73fb64fa..ff5939ff1 100644 --- a/man2/mremap.2 +++ b/man2/mremap.2 @@ -129,6 +129,22 @@ If is specified, then .B MREMAP_MAYMOVE must also be specified. +.TP +.BR MREMAP_DONTUNMAP " (since Linux 5.7)" +.\" commit e346b3813067d4b17383f975f197a9aa28a3b077 +This flag which must be used in conjunction with +.B MREMAP_MAYMOVE +remaps a mapping to a new address and it does not unmap the mapping at +.BR old_address . +This flag can only be used with private anonymous mappings. +Any access to the range specified at +.BR old_address +after completion will result in an anonymous page fault. +The anonymous page fault will be handled by a +.BR userfaultfd (2) +if the range was previously registered on the mapping specified by +.BR old_address . +Otherwise, it will be zero filled by the kernel. .PP If the memory segment specified by .I old_address @@ -176,6 +192,8 @@ a value other than .B MREMAP_MAYMOVE or .B MREMAP_FIXED +or +.B MREMAP_DONTUNMAP was specified in .IR flags ; .IP * @@ -197,9 +215,22 @@ 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 and +.BR old_address +that was not private anonymous; +.IP * +.B MREMAP_DONTUNMAP +was specified and +.BR old_size +was not equal to +.BR new_size ; +.IP * \fIold_size\fP was zero and \fIold_address\fP does not refer to a shareable mapping (but see BUGS); .IP * @@ -209,10 +240,20 @@ 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 causing a new mapping to be created that would exceed the +(virtual) memory available. +Or, it would exceed the maximum number of allowed mappings. +.RE .SH CONFORMING TO This call is Linux-specific, and should not be used in programs intended to be portable. @@ -238,6 +279,14 @@ call will make a best effort to populate the new area but will not fail with .B ENOMEM if the area cannot be populated. +.PP +The +.BR MREMAP_DONTUNMAP +flag may be used to atomically move a mapping while leaving the source +mapped. +Possible applications for this behavior might be garbage collection or +non-cooperative +.BR userfaultfd (2) . .SH BUGS Before Linux 4.14, if -- 2.26.0.110.g2183baf09c-goog
