From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f50.google.com (mail-pa0-f50.google.com [209.85.220.50]) by kanga.kvack.org (Postfix) with ESMTP id 157FA6B025C for ; Thu, 23 Jul 2015 16:52:06 -0400 (EDT) Received: by pachj5 with SMTP id hj5so1850514pac.3 for ; Thu, 23 Jul 2015 13:52:05 -0700 (PDT) Received: from mail-pa0-x236.google.com (mail-pa0-x236.google.com. [2607:f8b0:400e:c03::236]) by mx.google.com with ESMTPS id al7si14665986pad.160.2015.07.23.13.52.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Jul 2015 13:52:05 -0700 (PDT) Received: by pacan13 with SMTP id an13so1938092pac.1 for ; Thu, 23 Jul 2015 13:52:04 -0700 (PDT) Date: Thu, 23 Jul 2015 13:52:02 -0700 (PDT) From: David Rientjes Subject: Re: [patch] mmap.2: document the munmap exception for underlying page size In-Reply-To: <55B0E900.8090207@gmail.com> Message-ID: References: <55B027D3.4020608@oracle.com> <55B0E900.8090207@gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: "Michael Kerrisk (man-pages)" Cc: Mike Kravetz , Hugh Dickins , Davide Libenzi , Eric B Munson , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-man@vger.kernel.org On Thu, 23 Jul 2015, Michael Kerrisk (man-pages) wrote: > >> 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. > > And, surely, it also does something similar for mmap()'s 'addr' > argument? > > I suggest we add a subsection to describe the HugeTLB differences. How > about something like: > > Huge page (Huge TLB) mappings > For mappings that employ huge pages, the requirements for the > arguments of mmap() and munmap() differ somewhat from the > requirements for mappings that use the native system page size. > > For mmap(), offset must be a multiple of the underlying huge page > size. The system automatically aligns length to be a multiple of > the underlying huge page size. > > For munmap(), addr and length must both be a multiple of the > underlying huge page size. > ? > Looks good, please add my acked-by. The commit that expanded on the documentation of this behavior was 80d6b94bd69a7a49b52bf503ef6a841f43cf5bbb. Answering from your other email, no, this behavior in the kernel has not changed recently but we found it wasn't properly documented so we wanted to fix that both in the kernel tree and in the man-pages to make it explicit. -- 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