From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Kravetz Subject: Re: [patch] mmap.2: document the munmap exception for underlying page size Date: Wed, 22 Jul 2015 16:31:31 -0700 Message-ID: <55B027D3.4020608@oracle.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: David Rientjes , mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Cc: Hugh Dickins , Davide Libenzi , Eric B Munson , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-man@vger.kernel.org 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 > --- > 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. -- Mike Kravetz -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html