From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161229AbcFQUDz (ORCPT ); Fri, 17 Jun 2016 16:03:55 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:35476 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964798AbcFQUDt (ORCPT ); Fri, 17 Jun 2016 16:03:49 -0400 Date: Fri, 17 Jun 2016 22:03:46 +0200 From: Michal Hocko To: Richard Weinberger Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, hannes@cmpxchg.org, mgorman@techsingularity.net, n-horiguchi@ah.jp.nec.com, kirill.shutemov@linux.intel.com, hughd@google.com, vbabka@suse.cz, adrian.hunter@intel.com, dedekind1@gmail.com, hch@infradead.org, linux-fsdevel@vger.kernel.org, boris.brezillon@free-electrons.com, maxime.ripard@free-electrons.com, david@sigma-star.at, david@fromorbit.com, alex@nextthing.co, sasha.levin@oracle.com, iamjoonsoo.kim@lge.com, rvaswani@codeaurora.org, tony.luck@intel.com, shailendra.capricorn@gmail.com Subject: Re: [PATCH 1/3] mm: Don't blindly assign fallback_migrate_page() Message-ID: <20160617200345.GA4071@dhcp22.suse.cz> References: <1466112375-1717-1-git-send-email-richard@nod.at> <1466112375-1717-2-git-send-email-richard@nod.at> <20160616161121.35ee5183b9ef9f7b7dcbc815@linux-foundation.org> <5763A9B2.8060303@nod.at> <20160617162803.GK21670@dhcp22.suse.cz> <57642B91.4020206@nod.at> <20160617182751.GB692@dhcp22.suse.cz> <5764513E.2070102@nod.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5764513E.2070102@nod.at> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 17-06-16 21:36:30, Richard Weinberger wrote: > > > Am 17.06.2016 um 20:27 schrieb Michal Hocko: > > On Fri 17-06-16 18:55:45, Richard Weinberger wrote: > >> Am 17.06.2016 um 18:28 schrieb Michal Hocko: > >>> But doesn't this disable the page migration and so potentially reduce > >>> the compaction success rate for the large pile of filesystems? Without > >>> any hint about that? > >> > >> The WARN_ON_ONCE() is the hint. ;) > > > > Right. My reply turned a different way than I meant... I meant to say > > that there might be different regressions caused by this change without much > > hint that a particular warning would be the smoking gun... > > > > Okay, what about something like that? > That way everything works as before and we don't have regressions > but FS maintainers will notice the WARN_ON_ONCE() and hopefully review > whether generic_migrate_page() is really suitable. > If so, they can set their a_ops->migratepage to generic_migrate_page(). Yes this sounds better to me. I would just be more verbose about which a_ops is missing the migratepage callback. The WARN_ON_ONCE will not tell us which fs is the culprit. I am not even sure the calltrace is really helpful and maybe printk_once would be more appropriate. printk_once(KERN_INFO "%ps is missing migratepage callback. Please report to the respective filesystem maintainers.\n", mapping->a_ops); Or print once per a_ops would be even better but that sounds like an over engineering... > @@ -771,8 +773,15 @@ static int move_to_new_page(struct page *newpage, struct page *page, > * is the most common path for page migration. > */ > rc = mapping->a_ops->migratepage(mapping, newpage, page, mode); > - else > - rc = fallback_migrate_page(mapping, newpage, page, mode); > + else { > + /* > + * Dear filesystem maintainer, please verify whether > + * generic_migrate_page() is suitable for your > + * filesystem, especially wrt. page flag handling. > + */ > + WARN_ON_ONCE(1); > + rc = generic_migrate_page(mapping, newpage, page, mode); > + } > > /* > * When successful, old pagecache page->mapping must be cleared before > > Thanks, > //richard -- Michal Hocko SUSE Labs