From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) by kanga.kvack.org (Postfix) with ESMTP id B03D48E0002 for ; Thu, 20 Dec 2018 09:39:44 -0500 (EST) Received: by mail-pg1-f198.google.com with SMTP id s22so1663631pgv.8 for ; Thu, 20 Dec 2018 06:39:44 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id q19si2010363pfh.138.2018.12.20.06.39.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Dec 2018 06:39:43 -0800 (PST) Date: Thu, 20 Dec 2018 15:39:39 +0100 From: Michal Hocko Subject: Re: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages Message-ID: <20181220143939.GA6210@dhcp22.suse.cz> References: <20181217225113.17864-1-osalvador@suse.de> <20181219142528.yx6ravdyzcqp5wtd@master> <20181219233914.2fxe26pih26ifvmt@d104.suse.de> <20181220091228.GB14234@dhcp22.suse.cz> <20181220124925.itwuuacgztpgsk7s@d104.suse.de> <20181220130606.GG9104@dhcp22.suse.cz> <20181220134132.6ynretwlndmyupml@d104.suse.de> <20181220142124.r34fnuv6b33luj5a@d104.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181220142124.r34fnuv6b33luj5a@d104.suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador Cc: Wei Yang , akpm@linux-foundation.org, vbabka@suse.cz, pavel.tatashin@microsoft.com, rppt@linux.vnet.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 20-12-18 15:21:27, Oscar Salvador wrote: > On Thu, Dec 20, 2018 at 02:41:32PM +0100, Oscar Salvador wrote: > > On Thu, Dec 20, 2018 at 02:06:06PM +0100, Michal Hocko wrote: > > > You did want iter += skip_pages - 1 here right? > > > > Bleh, yeah. > > I am taking vacation today so my brain has left me hours ago, sorry. > > Should be: > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 4812287e56a0..0634fbdef078 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -8094,7 +8094,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, > > goto unmovable; > > > > skip_pages = (1 << compound_order(head)) - (page - head); > > - iter = round_up(iter + 1, skip_pages) - 1; > > + iter += skip_pages - 1; > > continue; > > } > > On a second thought, I think it should not really matter. > > AFAICS, we can have these scenarios: > > 1) the head page is the first page in the pabeblock > 2) first page in the pageblock is not a head but part of a hugepage > 3) the head is somewhere within the pageblock > > For cases 1) and 3), iter will just get the right value and we will > break the loop afterwards. > > In case 2), iter will be set to a value to skip over the remaining pages. > > I am assuming that hugepages are allocated and packed together. > > Note that I am not against the change, but I just wanted to see if there is > something I am missing. Yes, you are missing that this code should be as sane as possible ;) You are right that we are only processing one pageorder worth of pfns and that the page order is bound to HUGETLB_PAGE_ORDER _right_now_. But there is absolutely zero reason to hardcode that assumption into a simple loop, right? -- Michal Hocko SUSE Labs