From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f176.google.com (mail-ob0-f176.google.com [209.85.214.176]) by kanga.kvack.org (Postfix) with ESMTP id C62769003C7 for ; Wed, 22 Jul 2015 19:31:41 -0400 (EDT) Received: by obnw1 with SMTP id w1so143774961obn.3 for ; Wed, 22 Jul 2015 16:31:41 -0700 (PDT) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id y4si2358442oiy.21.2015.07.22.16.31.40 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Jul 2015 16:31:40 -0700 (PDT) Message-ID: <55B027D3.4020608@oracle.com> Date: Wed, 22 Jul 2015 16:31:31 -0700 From: Mike Kravetz MIME-Version: 1.0 Subject: Re: [patch] mmap.2: document the munmap exception for underlying page size References: In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes , mtk.manpages@gmail.com Cc: Hugh Dickins , Davide Libenzi , Eric B Munson , linux-kernel@vger.kernel.org, linux-mm@kvack.org, 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org