From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0CBAC17441 for ; Mon, 11 Nov 2019 23:18:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A405C2196E for ; Mon, 11 Nov 2019 23:18:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573514285; bh=rdJa61maE1ekeAOY2Gb+SEWYgZusibLnrBqmCvuYI+I=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=G7jDLTOVsB0EurEZKRrMXTvqN2GrQLn2OzrML+IVRvaVGpaYZxrrr7vv9/aRlOLqX 8CRiyin1W2EsiNapVqIPTWuwC3XOy9N7vcAIERPXW1Lsse+Yc3EbXiTKNIqEje+WQL IvC1RD8CkCpav6mikmrYnuYrswVZey2wIMgrYgXA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727208AbfKKXSE (ORCPT ); Mon, 11 Nov 2019 18:18:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:35260 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726845AbfKKXSE (ORCPT ); Mon, 11 Nov 2019 18:18:04 -0500 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B11632184C; Mon, 11 Nov 2019 23:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573514281; bh=rdJa61maE1ekeAOY2Gb+SEWYgZusibLnrBqmCvuYI+I=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=nvbJM84E2sEkK32e2Rv/AuBrrVuPQF/okvjjX0bzui9PswJjAGhUgUq8r4wALvWli UkeeqACkIOgTMr5zQXzoOxNAr/6PZY2GKZ1rXbPPfrXXajfiYfu3bbi4YckxU5WbPJ R4RHMpkbdVVMXzdwABPfTfauSPX5t3kcbdTIE5iI= Date: Mon, 11 Nov 2019 15:18:01 -0800 From: Andrew Morton To: Yang Shi Cc: mhocko@suse.com, mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: migrate: handle freed page at the first place Message-Id: <20191111151801.fb206aa84cc8ab3059994f7e@linux-foundation.org> In-Reply-To: <1573510165-113395-1-git-send-email-yang.shi@linux.alibaba.com> References: <1573510165-113395-1-git-send-email-yang.shi@linux.alibaba.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 Nov 2019 06:09:25 +0800 Yang Shi wrote: > When doing migration if the freed page is met, we just return without > migrating it since it is pointless to migrate a freed page. But, the > current code did two things before handling freed page: > > 1. Return -ENOMEM if the page is THP and THP migration is not supported. > 2. Allocate target page unconditionally. > > Both makes not too much sense. If we handle freed page at the first place > we don't have to worry about allocating/freeing target page and split > THP at all. > > For example (worst case) if we are trying to migrate a freed THP without > THP migration supported, the migrate_pages() would just split the THP then > retry to migrate base pages one by one by pointless allocating and freeing > pages, this is just waste of time. > > I didn't run into any actual problem with the current code (or I may > just not notice it yet), it was found by visual inspection. > > > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1170,13 +1170,6 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, > int rc = MIGRATEPAGE_SUCCESS; > struct page *newpage; > > - if (!thp_migration_supported() && PageTransHuge(page)) > - return -ENOMEM; > - > - newpage = get_new_page(page, private); > - if (!newpage) > - return -ENOMEM; > - > if (page_count(page) == 1) { Is it possible to have (!thp_migration_supported() && PageTransHuge(page) && page_count(page) == 1)? If so, isn't this new behviour? > /* page was freed from under us. So we are done. */ > ClearPageActive(page); > @@ -1187,13 +1180,16 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, > __ClearPageIsolated(page); > unlock_page(page); > } > - if (put_new_page) > - put_new_page(newpage, private); > - else > - put_page(newpage); > goto out; > } > > + if (!thp_migration_supported() && PageTransHuge(page)) > + return -ENOMEM; > + > + newpage = get_new_page(page, private); > + if (!newpage) > + return -ENOMEM; > + > rc = __unmap_and_move(page, newpage, force, mode); > if (rc == MIGRATEPAGE_SUCCESS) > set_page_owner_migrate_reason(newpage, reason);