From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH v7 3/6] mm: Introduce VM_LOCKONFAULT Date: Fri, 21 Aug 2015 09:25:52 +0200 Message-ID: <20150821072552.GF23723@dhcp22.suse.cz> References: <1439097776-27695-1-git-send-email-emunson@akamai.com> <1439097776-27695-4-git-send-email-emunson@akamai.com> <20150812115909.GA5182@dhcp22.suse.cz> <20150819213345.GB4536@akamai.com> <20150820075611.GD4780@dhcp22.suse.cz> <20150820170309.GA11557@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150820170309.GA11557-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Eric B Munson Cc: Andrew Morton , Vlastimil Babka , Jonathan Corbet , "Kirill A. Shutemov" , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: dri-devel@lists.freedesktop.org On Thu 20-08-15 13:03:09, Eric B Munson wrote: > On Thu, 20 Aug 2015, Michal Hocko wrote: > > > On Wed 19-08-15 17:33:45, Eric B Munson wrote: > > [...] > > > The group which asked for this feature here > > > wants the ability to distinguish between LOCKED and LOCKONFAULT regions > > > and without the VMA flag there isn't a way to do that. > > > > Could you be more specific on why this is needed? > > They want to keep metrics on the amount of memory used in a LOCKONFAULT > region versus the address space of the region. /proc//smaps already exports that information AFAICS. It exports VMA flags including VM_LOCKED and if rss < size then this is clearly LOCKONFAULT because the standard mlock semantic is to populate. Would that be sufficient? Now, it is true that LOCKONFAULT wouldn't be distinguishable from MAP_LOCKED which failed to populate but does that really matter? It is LOCKONFAULT in a way as well. > > > Do we know that these last two open flags are needed right now or is > > > this speculation that they will be and that none of the other VMA flags > > > can be reclaimed? > > > > I do not think they are needed by anybody right now but that is not a > > reason why it should be used without a really strong justification. > > If the discoverability is really needed then fair enough but I haven't > > seen any justification for that yet. > > To be completely clear you believe that if the metrics collection is > not a strong enough justification, it is better to expand the mm_struct > by another unsigned long than to use one of these bits right? A simple bool is sufficient for that. And yes I think we should go with per mm_struct flag rather than the additional vma flag if it has only the global (whole address space) scope - which would be the case if the LOCKONFAULT is always an mlock modifier and the persistance is needed only for MCL_FUTURE. Which is imho a sane semantic. -- Michal Hocko SUSE Labs