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 BB6838E0003 for ; Thu, 20 Dec 2018 00:22:22 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id b3so1102390edi.0 for ; Wed, 19 Dec 2018 21:22:22 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id j17-v6si7088470ejv.307.2018.12.19.21.22.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Dec 2018 21:22:21 -0800 (PST) Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wBK5IPU2156256 for ; Thu, 20 Dec 2018 00:22:20 -0500 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0b-001b2d01.pphosted.com with ESMTP id 2pg2s5n269-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 20 Dec 2018 00:22:19 -0500 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 20 Dec 2018 05:22:19 -0000 Subject: Re: [PATCH V5 1/3] mm: Add get_user_pages_cma_migrate References: <20181219034047.16305-1-aneesh.kumar@linux.ibm.com> <20181219034047.16305-2-aneesh.kumar@linux.ibm.com> From: "Aneesh Kumar K.V" Date: Thu, 20 Dec 2018 10:52:09 +0530 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Alexey Kardashevskiy , akpm@linux-foundation.org, Michal Hocko , mpe@ellerman.id.au, paulus@samba.org, David Gibson Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org On 12/20/18 9:49 AM, Alexey Kardashevskiy wrote: > > > On 19/12/2018 14:40, Aneesh Kumar K.V wrote: >> This helper does a get_user_pages_fast and if it find pages in the CMA area >> it will try to migrate them before taking page reference. This makes sure that >> we don't keep non-movable pages (due to page reference count) in the CMA area. >> Not able to move pages out of CMA area result in CMA allocation failures. >> >> Signed-off-by: Aneesh Kumar K.V > ..... >> + * We did migrate all the pages, Try to get the page references again >> + * migrating any new CMA pages which we failed to isolate earlier. >> + */ >> + drain_allow = true; >> + goto get_user_again; > > > So it is possible to have pages pinned, then successfully migrated > (migrate_pages() returned 0), then pinned again, then some pages may end > up in CMA again and migrate again and nothing seems to prevent this loop > from being endless. What do I miss? > pages used as target page for migration won't be allocated from CMA region. -aneesh