From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755062AbeDCI0k convert rfc822-to-8bit (ORCPT ); Tue, 3 Apr 2018 04:26:40 -0400 Received: from tyo162.gate.nec.co.jp ([114.179.232.162]:57551 "EHLO tyo162.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754850AbeDCI0j (ORCPT ); Tue, 3 Apr 2018 04:26:39 -0400 From: Naoya Horiguchi To: Michal Hocko CC: "linux-mm@kvack.org" , Andrew Morton , Vlastimil Babka , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v1] mm: consider non-anonymous thp as unmovable page Thread-Topic: [PATCH v1] mm: consider non-anonymous thp as unmovable page Thread-Index: AQHTywbBR3VGVrQJfUWs9ILMOA3NvqPuFnMAgAAG4YA= Date: Tue, 3 Apr 2018 08:24:06 +0000 Message-ID: <20180403082405.GA23809@hori1.linux.bs1.fc.nec.co.jp> References: <1522730788-24530-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20180403075928.GC5501@dhcp22.suse.cz> In-Reply-To: <20180403075928.GC5501@dhcp22.suse.cz> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.8] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <95C456C3C9681E43A23D653F1A98C7B7@gisp.nec.co.jp> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 03, 2018 at 09:59:28AM +0200, Michal Hocko wrote: > On Tue 03-04-18 13:46:28, Naoya Horiguchi wrote: > > My testing for the latest kernel supporting thp migration found out an > > infinite loop in offlining the memory block that is filled with shmem > > thps. We can get out of the loop with a signal, but kernel should > > return with failure in this case. > > > > What happens in the loop is that scan_movable_pages() repeats returning > > the same pfn without any progress. That's because page migration always > > fails for shmem thps. > > Why does it fail? Shmem pages should be movable without any issues. .. because try_to_unmap_one() explicitly skips unmapping for migration. #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION /* PMD-mapped THP migration entry */ if (!pvmw.pte && (flags & TTU_MIGRATION)) { VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page); if (!PageAnon(page)) continue; set_pmd_migration_entry(&pvmw, page); continue; } #endif When I implemented this code, I felt hard to work on both of anon thp and shmem thp at one time, so I separated the proposal into smaller steps. Shmem uses pagecache so we need some non-trivial effort (including testing) to extend thp migration for shmem. But I think it's a reasonable next step. Thanks, Naoya Horiguchi