From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id 9A8B16B000A for ; Tue, 9 Oct 2018 19:03:55 -0400 (EDT) Received: by mail-qk1-f199.google.com with SMTP id p73-v6so3164329qkp.2 for ; Tue, 09 Oct 2018 16:03:55 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id g4-v6si543014qvk.217.2018.10.09.16.03.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Oct 2018 16:03:54 -0700 (PDT) Date: Tue, 9 Oct 2018 19:03:52 -0400 From: Andrea Arcangeli Subject: Re: [PATCH 1/2] mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings Message-ID: <20181009230352.GE9307@redhat.com> References: <20180925120326.24392-2-mhocko@kernel.org> <20181005073854.GB6931@suse.de> <20181005232155.GA2298@redhat.com> <20181009094825.GC6931@suse.de> <20181009122745.GN8528@dhcp22.suse.cz> <20181009130034.GD6931@suse.de> <20181009142510.GU8528@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181009142510.GU8528@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Mel Gorman , David Rientjes , Andrew Morton , Vlastimil Babka , Andrea Argangeli , Zi Yan , Stefan Priebe - Profihost AG , "Kirill A. Shutemov" , linux-mm@kvack.org, LKML , Stable tree On Tue, Oct 09, 2018 at 04:25:10PM +0200, Michal Hocko wrote: > On Tue 09-10-18 14:00:34, Mel Gorman wrote: > > On Tue, Oct 09, 2018 at 02:27:45PM +0200, Michal Hocko wrote: > > > [Sorry for being slow in responding but I was mostly offline last few > > > days] > > > > > > On Tue 09-10-18 10:48:25, Mel Gorman wrote: > > > [...] > > > > This goes back to my point that the MADV_HUGEPAGE hint should not make > > > > promises about locality and that introducing MADV_LOCAL for specialised > > > > libraries may be more appropriate with the initial semantic being how it > > > > treats MADV_HUGEPAGE regions. > > > > > > I agree with your other points and not going to repeat them. I am not > > > sure madvise s the best API for the purpose though. We are talking about > > > memory policy here and there is an existing api for that so I would > > > _prefer_ to reuse it for this purpose. > > > > > > > I flip-flopped on that one in my head multiple times on the basis of > > how strict it should be. Memory policies tend to be black or white -- > > bind here, interleave there, etc. It wasn't clear to me what the best > > policy would be to describe "allocate local as best as you can but allow > > fallbacks if necessary". MPOL_PREFERRED is not black and white. In fact I asked David earlier if MPOL_PREFERRED could check if it would already be a good fit for this. Still the point is it requires privilege (and for a good reason). > I was thinking about MPOL_NODE_PROXIMITY with the following semantic: > - try hard to allocate from a local or very close numa node(s) even when > that requires expensive operations like the memory reclaim/compaction > before falling back to other more distant numa nodes. If MPOL_PREFERRED can't work something like this could be added. I think "madvise vs mbind" is more an issue of "no-permission vs permission" required. And if the processes ends up swapping out all other process with their memory already allocated in the node, I think some permission is correct to be required, in which case an mbind looks a better fit. MPOL_PREFERRED also looks a first candidate for investigation as it's already not black and white and allows spillover and may already do the right thing in fact if set on top of MADV_HUGEPAGE. Thanks, Andrea