From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV_DONTNEED hints Date: Tue, 03 Feb 2015 17:25:08 +0100 Message-ID: <54D0F664.3070606@gmail.com> References: <20150202165525.GM2395@suse.de> <54CFF8AC.6010102@intel.com> <54D08483.40209@suse.cz> <20150203111600.GR2395@suse.de> <20150203152121.GC8914@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150203152121.GC8914-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko , Mel Gorman Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, minchan Kim , Dave Hansen , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.orgMinchan Kim , Andrew Morton , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On 02/03/2015 04:21 PM, Michal Hocko wrote: > On Tue 03-02-15 11:16:00, Mel Gorman wrote: >> On Tue, Feb 03, 2015 at 09:19:15AM +0100, Vlastimil Babka wrote: > [...] >>> And if we agree that there is indeed no guarantee, what's the actual semantic >>> difference from MADV_FREE? I guess none? So there's only a possible perfomance >>> difference? >>> >> >> Timing. MADV_DONTNEED if it has an effect is immediate, is a heavier >> operations and RSS is reduced. MADV_FREE only has an impact in the future >> if there is memory pressure. > > JFTR. the man page for MADV_FREE has been proposed already > (https://lkml.org/lkml/2014/12/5/63 should be the last version AFAIR). I > do not see it in the man-pages git tree but the patch was not in time > for 3.19 so I guess it will only appear in 3.20. > Yikes! That patch was buried in the bottom of a locked filing cabinet in a disused lavatory. I unfortunately don't read every thread that comes my way, especially if it doesn't look like a man-pages patch (i.e., falls in the middle of an LKML thread that starts on another topic, and doesn't see linux-man@). I'll respond to that patch soon. (There are some problems that mean I could not accept it, AFAICT.) Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/