From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f171.google.com (mail-we0-f171.google.com [74.125.82.171]) by kanga.kvack.org (Postfix) with ESMTP id 02CFE6B0075 for ; Fri, 6 Feb 2015 15:45:42 -0500 (EST) Received: by mail-we0-f171.google.com with SMTP id k11so16004568wes.2 for ; Fri, 06 Feb 2015 12:45:41 -0800 (PST) Received: from mail-wi0-x231.google.com (mail-wi0-x231.google.com. [2a00:1450:400c:c05::231]) by mx.google.com with ESMTPS id l2si6075651wja.190.2015.02.06.12.45.38 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Feb 2015 12:45:39 -0800 (PST) Received: by mail-wi0-f177.google.com with SMTP id r20so5206267wiv.4 for ; Fri, 06 Feb 2015 12:45:38 -0800 (PST) Date: Fri, 6 Feb 2015 21:45:36 +0100 From: Michal Hocko Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints Message-ID: <20150206204536.GA24245@dhcp22.suse.cz> References: <54D08483.40209@suse.cz> <20150203105301.GC14259@node.dhcp.inet.fi> <54D0B43D.8000209@suse.cz> <54D0F56A.9050003@gmail.com> <54D22298.3040504@suse.cz> <54D2508A.9030804@suse.cz> <20150205154102.GA20607@dhcp22.suse.cz> <54D4E47E.4020509@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <54D4E47E.4020509@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Michael Kerrisk (man-pages)" Cc: Vlastimil Babka , "Kirill A. Shutemov" , Dave Hansen , Mel Gorman , "linux-mm@kvack.org" , Minchan Kim , Andrew Morton , lkml , Linux API , linux-man , Hugh Dickins On Fri 06-02-15 16:57:50, Michael Kerrisk wrote: [...] > > Yes, this wording is better because many users are not aware of > > MAP_ANON|MAP_SHARED being file backed in fact and mmap man page doesn't > > mention that. > > (Michal, would you have a text to propose to add to the mmap(2) page? > Maybe it would be useful to add something there.) I am half way on vacation, but I can cook a patch after I am back after week. > > I am just wondering whether it makes sense to mention that MADV_DONTNEED > > for shared mappings might be surprising and not freeing the backing > > pages thus not really freeing memory until there is a memory > > pressure. But maybe this is too implementation specific for a man > > page. What about the following wording on top of yours? > > " > > Please note that the MADV_DONTNEED hint on shared mappings might not > > lead to immediate freeing of pages in the range. The kernel is free to > > delay this until an appropriate moment. RSS of the calling process will > > be reduced however. > > " > > Thanks! I added this, but dropped in the word "immediately" in the last > sentence, since I assume that was implied. So now we have: > > After a successful MADV_DONTNEED operation, the semana?? > tics of memory access in the specified region are > changed: subsequent accesses of pages in the range will > succeed, but will result in either repopulating the mema?? > ory contents from the up-to-date contents of the undera?? > lying mapped file (for shared file mappings, shared > anonymous mappings, and shmem-based techniques such as > System V shared memory segments) or zero-fill-on-demand > pages for anonymous private mappings. > > Note that, when applied to shared mappings, MADV_DONTa?? > NEED might not lead to immediate freeing of the pages in > the range. The kernel is free to delay freeing the > pages until an appropriate moment. The resident set > size (RSS) of the calling process will be immediately > reduced however. This sounds good to me and it is definitely much better than the current state. Thanks! > The current draft of the page can be found in a branch, > http://git.kernel.org/cgit/docs/man-pages/man-pages.git/log/?h=draft_madvise > > Thanks, > > Michael > > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ -- Michal Hocko SUSE Labs -- 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