On Wed, 22 Jul 2015, Mike Kravetz wrote:
> On 07/21/2015 05:41 PM, David Rientjes wrote:
> > munmap(2) will fail with an errno of EINVAL for hugetlb memory if the
> > length is not a multiple of the underlying page size.
> >
> > Documentation/vm/hugetlbpage.txt was updated to specify this behavior
> > since Linux 4.1 in commit 80d6b94bd69a ("mm, doc: cleanup and clarify
> > munmap behavior for hugetlb memory").
> >
> > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> > ---
> > man2/mmap.2 | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/man2/mmap.2 b/man2/mmap.2
> > --- a/man2/mmap.2
> > +++ b/man2/mmap.2
> > @@ -383,6 +383,10 @@ All pages containing a part
> > of the indicated range are unmapped, and subsequent references
> > to these pages will generate
> > .BR SIGSEGV .
> > +An exception is when the underlying memory is not of the native page
> > +size, such as hugetlb page sizes, whereas
> > +.I length
> > +must be a multiple of the underlying page size.
> > It is not an error if the
> > indicated range does not contain any mapped pages.
> > .SS Timestamps changes for file-backed mappings
> >
> > --
>
> Should we also add a similar comment for the mmap offset? Currently
> the man page says:
>
> "offset must be a multiple of the page size as returned by
> sysconf(_SC_PAGE_SIZE)."
>
> For hugetlbfs, I beieve the offset must be a multiple of the
> hugetlb page size. A similar comment/exception about using
> the "underlying page size" would apply here as well.
>
Yes, that makes sense, thanks. We should also explicitly say that mmap(2)
automatically aligns length to be hugepage aligned if backed by hugetlbfs.
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