Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758127AbbBEPlK (ORCPT ); Thu, 5 Feb 2015 10:41:10 -0500 Received: from cantor2.suse.de ([195.135.220.15]:57062 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753763AbbBEPlG (ORCPT ); Thu, 5 Feb 2015 10:41:06 -0500 Date: Thu, 5 Feb 2015 16:41:02 +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: <20150205154102.GA20607@dhcp22.suse.cz> References: <20150202165525.GM2395@suse.de> <54CFF8AC.6010102@intel.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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: 1897 Lines: 46 On Wed 04-02-15 20:24:27, Michael Kerrisk wrote: [...] > So, how about this text: > > 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 reloading of > the memory contents from the underlying mapped file " result in either providing the up-to-date contents of the underlying mapped file " Would be more precise IMO because reload might be interpreted as a major fault which is not necessarily the case (see below). > (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. 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. 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. " -- 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/