From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 885F86B0010 for ; Wed, 3 Oct 2018 07:48:47 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id x24-v6so3100615edm.13 for ; Wed, 03 Oct 2018 04:48:47 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h33-v6si971166edb.423.2018.10.03.04.48.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Oct 2018 04:48:46 -0700 (PDT) Date: Wed, 3 Oct 2018 13:48:42 +0200 From: Michal Hocko Subject: Re: [PATCH 1/4] mm/hugetlb: Enable PUD level huge page migration Message-ID: <20181003114842.GD4714@dhcp22.suse.cz> References: <1538482531-26883-1-git-send-email-anshuman.khandual@arm.com> <1538482531-26883-2-git-send-email-anshuman.khandual@arm.com> <20181002123909.GS18290@dhcp22.suse.cz> <20181003065833.GD18290@dhcp22.suse.cz> <7f0488b5-053f-0954-9b95-8c0890ef5597@arm.com> <20181003105926.GA4714@dhcp22.suse.cz> <34b25855-fcef-61ed-312d-2011f80bdec4@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34b25855-fcef-61ed-312d-2011f80bdec4@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Anshuman Khandual Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, punit.agrawal@arm.com, will.deacon@arm.com, Steven.Price@arm.com, catalin.marinas@arm.com, mike.kravetz@oracle.com, n-horiguchi@ah.jp.nec.com On Wed 03-10-18 17:07:13, Anshuman Khandual wrote: > > > On 10/03/2018 04:29 PM, Michal Hocko wrote: [...] > > It is not the platform that decides. That is the whole point of the > > distinction. It is us to say what is feasible and what we want to > > support. Do we want to support giga pages in zone_movable? Under which > > conditions? See my point? > > So huge_movable() is going to be a generic MM function deciding on the > feasibility for allocating a huge page of 'size' from movable zone during > migration. Yeah, this might be a more complex logic than just the size check. If there is a sufficient pre-allocated pool to migrate the page off it might be pre-reserved for future migration etc... Nothing to be done right now of course. > If the feasibility turns out to be negative, then migration > process is aborted there. You are still confusing allocation and migration here I am afraid. The whole "feasible to migrate" is for the _allocation_ time when we decide whether the new page should be placed in zone_movable or not. > huge_movable() will do something like these: > > - Return positive right away on smaller size huge pages > - Measure movable allocation feasibility for bigger huge pages > - Look out for free_pages in the huge page order in movable areas > - if (order > (MAX_ORDER - 1)) > - Scan the PFN ranges in movable zone for possible allocation > - etc > - etc > > Did I get this right ? Well, not really. I was thinking of something like this for the beginning if (!arch_hugepage_migration_supporte()) return false; if (hstate_is_gigantic(h)) return false; return true; further changes might be done on top of this. -- Michal Hocko SUSE Labs