Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755268AbbBFUpm (ORCPT ); Fri, 6 Feb 2015 15:45:42 -0500 Received: from mail-wg0-f52.google.com ([74.125.82.52]:56458 "EHLO mail-wg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754165AbbBFUpk (ORCPT ); Fri, 6 Feb 2015 15:45:40 -0500 Date: Fri, 6 Feb 2015 21:45:36 +0100 From: Michal Hocko 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 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> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2912 Lines: 69 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 seman‐ > 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 mem‐ > ory contents from the up-to-date contents of the under‐ > 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_DONT‐ > 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 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/