Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753401AbbGWNF7 (ORCPT ); Thu, 23 Jul 2015 09:05:59 -0400 Received: from mail-wi0-f181.google.com ([209.85.212.181]:37185 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752574AbbGWNFY (ORCPT ); Thu, 23 Jul 2015 09:05:24 -0400 Message-ID: <55B0E690.3040601@gmail.com> Date: Thu, 23 Jul 2015 15:05:20 +0200 From: "Michael Kerrisk (man-pages)" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: David Rientjes CC: mtk.manpages@gmail.com, Hugh Dickins , Davide Libenzi , Eric B Munson , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-man@vger.kernel.org Subject: Re: [patch] mmap.2: document the munmap exception for underlying page size References: <55AFD009.6080706@gmail.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2724 Lines: 72 On 07/23/2015 12:03 AM, David Rientjes wrote: > On Wed, 22 Jul 2015, Michael Kerrisk (man-pages) wrote: > >>> 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 >> >> I'm struggling a bit to understand your text. Is the point this: >> >> If we have a hugetlb area, then the munmap() length >> must be a multiple of the page size. >> >> ? >> > > Of the hugetlb page size, yes, which was meant by the "underlying page > size" since we have configurable hugetlb sizes. This is different from > the native page size, whereas the length is rounded up to be page aligned > per POSIX. > >> Are there any requirements about 'addr'? Must it also me huge-page-aligned? >> > > Yes, so it looks like we need to fix up the reference to "address addr > must be a multiple of the page size" to something like "address addr must > be a multiple of the underlying page size" but I think the distinction > isn't explicit enough as I'd like it. I think it's better to explicitly > show the exception for hugetlb page sizes and compare the underlying page > size to the native page size to define how the behavior differs. > > Would something like > > An exception is when the underlying memory, such as hugetlb > memory, is not of the native page size: the address addr and > the length must be a multiple of the underlying page size. See my suggestion in another mail (in a few minutes). > suffice? > > Also, is it typical to reference the commit of the documentation change > in the kernel source that defines this? I see this done with .\" blocks > for MAP_STACK in the same man page. I find it handy to add such references, for later references. By the way, are you saying that some piece of behavior has changed in recent times for munmap() on HugeTLB? Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/